@chapter Filtering Introduction
@c man begin FILTERING INTRODUCTION

Filtering in FFmpeg is enabled through the libavfilter library.

Libavfilter is the filtering API of FFmpeg. It is the substitute of
the now deprecated 'vhooks' and started as a Google Summer of Code
project.

Audio filtering integration into the main FFmpeg repository is a work in
progress, so audio API and ABI should not be considered stable yet.

In libavfilter, it is possible for filters to have multiple inputs and
multiple outputs.
To illustrate the sorts of things that are possible, we can
use a complex filter graph. For example, the following one:

@example
input --> split --> fifo -----------------------> overlay --> output
            |                                        ^
            |                                        |
            +------> fifo --> crop --> vflip --------+
@end example

splits the stream in two streams, sends one stream through the crop filter
and the vflip filter before merging it back with the other stream by
overlaying it on top. You can use the following command to achieve this:

@example
ffmpeg -i input -vf "[in] split [T1], fifo, [T2] overlay=0:H/2 [out]; [T1] fifo, crop=iw:ih/2:0:ih/2, vflip [T2]" output
@end example

The result will be that in output the top half of the video is mirrored
onto the bottom half.

Filters are loaded using the @var{-vf} or @var{-af} option passed to
@command{ffmpeg} or to @command{ffplay}. Filters in the same linear
chain are separated by commas. In our example, @var{split, fifo,
overlay} are in one linear chain, and @var{fifo, crop, vflip} are in
another. The points where the linear chains join are labeled by names
enclosed in square brackets. In our example, that is @var{[T1]} and
@var{[T2]}. The special labels @var{[in]} and @var{[out]} are the points
where video is input and output.

Some filters take in input a list of parameters: they are specified
after the filter name and an equal sign, and are separated from each other
by a colon.

There exist so-called @var{source filters} that do not have an
audio/video input, and @var{sink filters} that will not have audio/video
output.

@c man end FILTERING INTRODUCTION

@chapter graph2dot
@c man begin GRAPH2DOT

The @file{graph2dot} program included in the FFmpeg @file{tools}
directory can be used to parse a filter graph description and issue a
corresponding textual representation in the dot language.

Invoke the command:
@example
graph2dot -h
@end example

to see how to use @file{graph2dot}.

You can then pass the dot description to the @file{dot} program (from
the graphviz suite of programs) and obtain a graphical representation
of the filter graph.

For example the sequence of commands:
@example
echo @var{GRAPH_DESCRIPTION} | \
tools/graph2dot -o graph.tmp && \
dot -Tpng graph.tmp -o graph.png && \
display graph.png
@end example

can be used to create and display an image representing the graph
described by the @var{GRAPH_DESCRIPTION} string.

@c man end GRAPH2DOT

@chapter Filtergraph description
@c man begin FILTERGRAPH DESCRIPTION

A filtergraph is a directed graph of connected filters. It can contain
cycles, and there can be multiple links between a pair of
filters. Each link has one input pad on one side connecting it to one
filter from which it takes its input, and one output pad on the other
side connecting it to the one filter accepting its output.

Each filter in a filtergraph is an instance of a filter class
registered in the application, which defines the features and the
number of input and output pads of the filter.

A filter with no input pads is called a "source", a filter with no
output pads is called a "sink".

@anchor{Filtergraph syntax}
@section Filtergraph syntax

A filtergraph can be represented using a textual representation, which is
recognized by the @option{-filter}/@option{-vf} and @option{-filter_complex}
options in @command{ffmpeg} and @option{-vf} in @command{ffplay}, and by the
@code{avfilter_graph_parse()}/@code{avfilter_graph_parse2()} function defined in
@file{libavfilter/avfiltergraph.h}.

A filterchain consists of a sequence of connected filters, each one
connected to the previous one in the sequence. A filterchain is
represented by a list of ","-separated filter descriptions.

A filtergraph consists of a sequence of filterchains. A sequence of
filterchains is represented by a list of ";"-separated filterchain
descriptions.

A filter is represented by a string of the form:
[@var{in_link_1}]...[@var{in_link_N}]@var{filter_name}=@var{arguments}[@var{out_link_1}]...[@var{out_link_M}]

@var{filter_name} is the name of the filter class of which the
described filter is an instance of, and has to be the name of one of
the filter classes registered in the program.
The name of the filter class is optionally followed by a string
"=@var{arguments}".

@var{arguments} is a string which contains the parameters used to
initialize the filter instance, and are described in the filter
descriptions below.

The list of arguments can be quoted using the character "'" as initial
and ending mark, and the character '\' for escaping the characters
within the quoted text; otherwise the argument string is considered
terminated when the next special character (belonging to the set
"[]=;,") is encountered.

The name and arguments of the filter are optionally preceded and
followed by a list of link labels.
A link label allows to name a link and associate it to a filter output
or input pad. The preceding labels @var{in_link_1}
... @var{in_link_N}, are associated to the filter input pads,
the following labels @var{out_link_1} ... @var{out_link_M}, are
associated to the output pads.

When two link labels with the same name are found in the
filtergraph, a link between the corresponding input and output pad is
created.

If an output pad is not labelled, it is linked by default to the first
unlabelled input pad of the next filter in the filterchain.
For example in the filterchain:
@example
nullsrc, split[L1], [L2]overlay, nullsink
@end example
the split filter instance has two output pads, and the overlay filter
instance two input pads. The first output pad of split is labelled
"L1", the first input pad of overlay is labelled "L2", and the second
output pad of split is linked to the second input pad of overlay,
which are both unlabelled.

In a complete filterchain all the unlabelled filter input and output
pads must be connected. A filtergraph is considered valid if all the
filter input and output pads of all the filterchains are connected.

Libavfilter will automatically insert scale filters where format
conversion is required. It is possible to specify swscale flags
for those automatically inserted scalers by prepending
@code{sws_flags=@var{flags};}
to the filtergraph description.

Follows a BNF description for the filtergraph syntax:
@example
@var{NAME}             ::= sequence of alphanumeric characters and '_'
@var{LINKLABEL}        ::= "[" @var{NAME} "]"
@var{LINKLABELS}       ::= @var{LINKLABEL} [@var{LINKLABELS}]
@var{FILTER_ARGUMENTS} ::= sequence of chars (eventually quoted)
@var{FILTER}           ::= [@var{LINKNAMES}] @var{NAME} ["=" @var{ARGUMENTS}] [@var{LINKNAMES}]
@var{FILTERCHAIN}      ::= @var{FILTER} [,@var{FILTERCHAIN}]
@var{FILTERGRAPH}      ::= [sws_flags=@var{flags};] @var{FILTERCHAIN} [;@var{FILTERGRAPH}]
@end example

@c man end FILTERGRAPH DESCRIPTION

@chapter Audio Filters
@c man begin AUDIO FILTERS

When you configure your FFmpeg build, you can disable any of the
existing filters using @code{--disable-filters}.
The configure output will show the audio filters included in your
build.

Below is a description of the currently available audio filters.

@section aconvert

Convert the input audio format to the specified formats.

The filter accepts a string of the form:
"@var{sample_format}:@var{channel_layout}".

@var{sample_format} specifies the sample format, and can be a string or the
corresponding numeric value defined in @file{libavutil/samplefmt.h}. Use 'p'
suffix for a planar sample format.

@var{channel_layout} specifies the channel layout, and can be a string
or the corresponding number value defined in @file{libavutil/audioconvert.h}.

The special parameter "auto", signifies that the filter will
automatically select the output format depending on the output filter.

Some examples follow.

@itemize
@item
Convert input to float, planar, stereo:
@example
aconvert=fltp:stereo
@end example

@item
Convert input to unsigned 8-bit, automatically select out channel layout:
@example
aconvert=u8:auto
@end example
@end itemize

@section aformat

Convert the input audio to one of the specified formats. The framework will
negotiate the most appropriate format to minimize conversions.

The filter accepts the following named parameters:
@table @option

@item sample_fmts
A comma-separated list of requested sample formats.

@item sample_rates
A comma-separated list of requested sample rates.

@item channel_layouts
A comma-separated list of requested channel layouts.

@end table

If a parameter is omitted, all values are allowed.

For example to force the output to either unsigned 8-bit or signed 16-bit stereo:
@example
aformat=sample_fmts\=u8\,s16:channel_layouts\=stereo
@end example

@section amerge

Merge two or more audio streams into a single multi-channel stream.

The filter accepts the following named options:

@table @option

@item inputs
Set the number of inputs. Default is 2.

@end table

If the channel layouts of the inputs are disjoint, and therefore compatible,
the channel layout of the output will be set accordingly and the channels
will be reordered as necessary. If the channel layouts of the inputs are not
disjoint, the output will have all the channels of the first input then all
the channels of the second input, in that order, and the channel layout of
the output will be the default value corresponding to the total number of
channels.

For example, if the first input is in 2.1 (FL+FR+LF) and the second input
is FC+BL+BR, then the output will be in 5.1, with the channels in the
following order: a1, a2, b1, a3, b2, b3 (a1 is the first channel of the
first input, b1 is the first channel of the second input).

On the other hand, if both input are in stereo, the output channels will be
in the default order: a1, a2, b1, b2, and the channel layout will be
arbitrarily set to 4.0, which may or may not be the expected value.

All inputs must have the same sample rate, and format.

If inputs do not have the same duration, the output will stop with the
shortest.

Example: merge two mono files into a stereo stream:
@example
amovie=left.wav [l] ; amovie=right.mp3 [r] ; [l] [r] amerge
@end example

Example: multiple merges:
@example
ffmpeg -f lavfi -i "
amovie=input.mkv:si=0 [a0];
amovie=input.mkv:si=1 [a1];
amovie=input.mkv:si=2 [a2];
amovie=input.mkv:si=3 [a3];
amovie=input.mkv:si=4 [a4];
amovie=input.mkv:si=5 [a5];
[a0][a1][a2][a3][a4][a5] amerge=inputs=6" -c:a pcm_s16le output.mkv
@end example

@section amix

Mixes multiple audio inputs into a single output.

For example
@example
ffmpeg -i INPUT1 -i INPUT2 -i INPUT3 -filter_complex amix=inputs=3:duration=first:dropout_transition=3 OUTPUT
@end example
will mix 3 input audio streams to a single output with the same duration as the
first input and a dropout transition time of 3 seconds.

The filter accepts the following named parameters:
@table @option

@item inputs
Number of inputs. If unspecified, it defaults to 2.

@item duration
How to determine the end-of-stream.
@table @option

@item longest
Duration of longest input. (default)

@item shortest
Duration of shortest input.

@item first
Duration of first input.

@end table

@item dropout_transition
Transition time, in seconds, for volume renormalization when an input
stream ends. The default value is 2 seconds.

@end table

@section anull

Pass the audio source unchanged to the output.

@section aresample

Resample the input audio to the specified sample rate.

The filter accepts exactly one parameter, the output sample rate. If not
specified then the filter will automatically convert between its input
and output sample rates.

For example, to resample the input audio to 44100Hz:
@example
aresample=44100
@end example

@section asetnsamples

Set the number of samples per each output audio frame.

The last output packet may contain a different number of samples, as
the filter will flush all the remaining samples when the input audio
signal its end.

The filter accepts parameters as a list of @var{key}=@var{value} pairs,
separated by ":".

@table @option

@item nb_out_samples, n
Set the number of frames per each output audio frame. The number is
intended as the number of samples @emph{per each channel}.
Default value is 1024.

@item pad, p
If set to 1, the filter will pad the last audio frame with zeroes, so
that the last frame will contain the same number of samples as the
previous ones. Default value is 1.
@end table

For example, to set the number of per-frame samples to 1234 and
disable padding for the last frame, use:
@example
asetnsamples=n=1234:p=0
@end example

@section ashowinfo

Show a line containing various information for each input audio frame.
The input audio is not modified.

The shown line contains a sequence of key/value pairs of the form
@var{key}:@var{value}.

A description of each shown parameter follows:

@table @option
@item n
sequential number of the input frame, starting from 0

@item pts
presentation TimeStamp of the input frame, expressed as a number of
time base units. The time base unit depends on the filter input pad, and
is usually 1/@var{sample_rate}.

@item pts_time
presentation TimeStamp of the input frame, expressed as a number of
seconds

@item pos
position of the frame in the input stream, -1 if this information in
unavailable and/or meaningless (for example in case of synthetic audio)

@item fmt
sample format name

@item chlayout
channel layout description

@item nb_samples
number of samples (per each channel) contained in the filtered frame

@item rate
sample rate for the audio frame

@item checksum
Adler-32 checksum (printed in hexadecimal) of all the planes of the input frame

@item plane_checksum
Adler-32 checksum (printed in hexadecimal) for each input frame plane,
expressed in the form "[@var{c0} @var{c1} @var{c2} @var{c3} @var{c4} @var{c5}
@var{c6} @var{c7}]"
@end table

@section asplit

Split input audio into several identical outputs.

The filter accepts a single parameter which specifies the number of outputs. If
unspecified, it defaults to 2.

For example:
@example
[in] asplit [out0][out1]
@end example

will create two separate outputs from the same input.

To create 3 or more outputs, you need to specify the number of
outputs, like in:
@example
[in] asplit=3 [out0][out1][out2]
@end example

@example
ffmpeg -i INPUT -filter_complex asplit=5 OUTPUT
@end example
will create 5 copies of the input audio.


@section astreamsync

Forward two audio streams and control the order the buffers are forwarded.

The argument to the filter is an expression deciding which stream should be
forwarded next: if the result is negative, the first stream is forwarded; if
the result is positive or zero, the second stream is forwarded. It can use
the following variables:

@table @var
@item b1 b2
number of buffers forwarded so far on each stream
@item s1 s2
number of samples forwarded so far on each stream
@item t1 t2
current timestamp of each stream
@end table

The default value is @code{t1-t2}, which means to always forward the stream
that has a smaller timestamp.

Example: stress-test @code{amerge} by randomly sending buffers on the wrong
input, while avoiding too much of a desynchronization:
@example
amovie=file.ogg [a] ; amovie=file.mp3 [b] ;
[a] [b] astreamsync=(2*random(1))-1+tanh(5*(t1-t2)) [a2] [b2] ;
[a2] [b2] amerge
@end example

@section atempo

Adjust audio tempo.

The filter accepts exactly one parameter, the audio tempo. If not
specified then the filter will assume nominal 1.0 tempo. Tempo must
be in the [0.5, 2.0] range.

For example, to slow down audio to 80% tempo:
@example
atempo=0.8
@end example

For example, to speed up audio to 125% tempo:
@example
atempo=1.25
@end example

@section earwax

Make audio easier to listen to on headphones.

This filter adds `cues' to 44.1kHz stereo (i.e. audio CD format) audio
so that when listened to on headphones the stereo image is moved from
inside your head (standard for headphones) to outside and in front of
the listener (standard for speakers).

Ported from SoX.

@section pan

Mix channels with specific gain levels. The filter accepts the output
channel layout followed by a set of channels definitions.

This filter is also designed to remap efficiently the channels of an audio
stream.

The filter accepts parameters of the form:
"@var{l}:@var{outdef}:@var{outdef}:..."

@table @option
@item l
output channel layout or number of channels

@item outdef
output channel specification, of the form:
"@var{out_name}=[@var{gain}*]@var{in_name}[+[@var{gain}*]@var{in_name}...]"

@item out_name
output channel to define, either a channel name (FL, FR, etc.) or a channel
number (c0, c1, etc.)

@item gain
multiplicative coefficient for the channel, 1 leaving the volume unchanged

@item in_name
input channel to use, see out_name for details; it is not possible to mix
named and numbered input channels
@end table

If the `=' in a channel specification is replaced by `<', then the gains for
that specification will be renormalized so that the total is 1, thus
avoiding clipping noise.

@subsection Mixing examples

For example, if you want to down-mix from stereo to mono, but with a bigger
factor for the left channel:
@example
pan=1:c0=0.9*c0+0.1*c1
@end example

A customized down-mix to stereo that works automatically for 3-, 4-, 5- and
7-channels surround:
@example
pan=stereo: FL < FL + 0.5*FC + 0.6*BL + 0.6*SL : FR < FR + 0.5*FC + 0.6*BR + 0.6*SR
@end example

Note that @command{ffmpeg} integrates a default down-mix (and up-mix) system
that should be preferred (see "-ac" option) unless you have very specific
needs.

@subsection Remapping examples

The channel remapping will be effective if, and only if:

@itemize
@item gain coefficients are zeroes or ones,
@item only one input per channel output,
@end itemize

If all these conditions are satisfied, the filter will notify the user ("Pure
channel mapping detected"), and use an optimized and lossless method to do the
remapping.

For example, if you have a 5.1 source and want a stereo audio stream by
dropping the extra channels:
@example
pan="stereo: c0=FL : c1=FR"
@end example

Given the same source, you can also switch front left and front right channels
and keep the input channel layout:
@example
pan="5.1: c0=c1 : c1=c0 : c2=c2 : c3=c3 : c4=c4 : c5=c5"
@end example

If the input is a stereo audio stream, you can mute the front left channel (and
still keep the stereo channel layout) with:
@example
pan="stereo:c1=c1"
@end example

Still with a stereo audio stream input, you can copy the right channel in both
front left and right:
@example
pan="stereo: c0=FR : c1=FR"
@end example

@section silencedetect

Detect silence in an audio stream.

This filter logs a message when it detects that the input audio volume is less
or equal to a noise tolerance value for a duration greater or equal to the
minimum detected noise duration.

The printed times and duration are expressed in seconds.

@table @option
@item duration, d
Set silence duration until notification (default is 2 seconds).

@item noise, n
Set noise tolerance. Can be specified in dB (in case "dB" is appended to the
specified value) or amplitude ratio. Default is -60dB, or 0.001.
@end table

Detect 5 seconds of silence with -50dB noise tolerance:
@example
silencedetect=n=-50dB:d=5
@end example

Complete example with @command{ffmpeg} to detect silence with 0.0001 noise
tolerance in @file{silence.mp3}:
@example
ffmpeg -f lavfi -i amovie=silence.mp3,silencedetect=noise=0.0001 -f null -
@end example

@section volume

Adjust the input audio volume.

The filter accepts exactly one parameter @var{vol}, which expresses
how the audio volume will be increased or decreased.

Output values are clipped to the maximum value.

If @var{vol} is expressed as a decimal number, the output audio
volume is given by the relation:
@example
@var{output_volume} = @var{vol} * @var{input_volume}
@end example

If @var{vol} is expressed as a decimal number followed by the string
"dB", the value represents the requested change in decibels of the
input audio power, and the output audio volume is given by the
relation:
@example
@var{output_volume} = 10^(@var{vol}/20) * @var{input_volume}
@end example

Otherwise @var{vol} is considered an expression and its evaluated
value is used for computing the output audio volume according to the
first relation.

Default value for @var{vol} is 1.0.

@subsection Examples

@itemize
@item
Half the input audio volume:
@example
volume=0.5
@end example

The above example is equivalent to:
@example
volume=1/2
@end example

@item
Decrease input audio power by 12 decibels:
@example
volume=-12dB
@end example
@end itemize

@section asyncts
Synchronize audio data with timestamps by squeezing/stretching it and/or
dropping samples/adding silence when needed.

The filter accepts the following named parameters:
@table @option

@item compensate
Enable stretching/squeezing the data to make it match the timestamps.

@item min_delta
Minimum difference between timestamps and audio data (in seconds) to trigger
adding/dropping samples.

@item max_comp
Maximum compensation in samples per second.

@end table

@section channelsplit
Split each channel in input audio stream into a separate output stream.

This filter accepts the following named parameters:
@table @option
@item channel_layout
Channel layout of the input stream. Default is "stereo".
@end table

For example, assuming a stereo input MP3 file
@example
ffmpeg -i in.mp3 -filter_complex channelsplit out.mkv
@end example
will create an output Matroska file with two audio streams, one containing only
the left channel and the other the right channel.

To split a 5.1 WAV file into per-channel files
@example
ffmpeg -i in.wav -filter_complex
'channelsplit=channel_layout=5.1[FL][FR][FC][LFE][SL][SR]'
-map '[FL]' front_left.wav -map '[FR]' front_right.wav -map '[FC]'
front_center.wav -map '[LFE]' lfe.wav -map '[SL]' side_left.wav -map '[SR]'
side_right.wav
@end example

@section channelmap
Remap input channels to new locations.

This filter accepts the following named parameters:
@table @option
@item channel_layout
Channel layout of the output stream.

@item map
Map channels from input to output. The argument is a comma-separated list of
mappings, each in the @code{@var{in_channel}-@var{out_channel}} or
@var{in_channel} form. @var{in_channel} can be either the name of the input
channel (e.g. FL for front left) or its index in the input channel layout.
@var{out_channel} is the name of the output channel or its index in the output
channel layout. If @var{out_channel} is not given then it is implicitly an
index, starting with zero and increasing by one for each mapping.
@end table

If no mapping is present, the filter will implicitly map input channels to
output channels preserving index.

For example, assuming a 5.1+downmix input MOV file
@example
ffmpeg -i in.mov -filter 'channelmap=map=DL-FL\,DR-FR' out.wav
@end example
will create an output WAV file tagged as stereo from the downmix channels of
the input.

To fix a 5.1 WAV improperly encoded in AAC's native channel order
@example
ffmpeg -i in.wav -filter 'channelmap=1\,2\,0\,5\,3\,4:channel_layout=5.1' out.wav
@end example

@section join
Join multiple input streams into one multi-channel stream.

The filter accepts the following named parameters:
@table @option

@item inputs
Number of input streams. Defaults to 2.

@item channel_layout
Desired output channel layout. Defaults to stereo.

@item map
Map channels from inputs to output. The argument is a comma-separated list of
mappings, each in the @code{@var{input_idx}.@var{in_channel}-@var{out_channel}}
form. @var{input_idx} is the 0-based index of the input stream. @var{in_channel}
can be either the name of the input channel (e.g. FL for front left) or its
index in the specified input stream. @var{out_channel} is the name of the output
channel.
@end table

The filter will attempt to guess the mappings when those are not specified
explicitly. It does so by first trying to find an unused matching input channel
and if that fails it picks the first unused input channel.

E.g. to join 3 inputs (with properly set channel layouts)
@example
ffmpeg -i INPUT1 -i INPUT2 -i INPUT3 -filter_complex join=inputs=3 OUTPUT
@end example

To build a 5.1 output from 6 single-channel streams:
@example
ffmpeg -i fl -i fr -i fc -i sl -i sr -i lfe -filter_complex
'join=inputs=6:channel_layout=5.1:map=0.0-FL\,1.0-FR\,2.0-FC\,3.0-SL\,4.0-SR\,5.0-LFE'
out
@end example

@section resample
Convert the audio sample format, sample rate and channel layout. This filter is
not meant to be used directly.

@c man end AUDIO FILTERS

@chapter Audio Sources
@c man begin AUDIO SOURCES

Below is a description of the currently available audio sources.

@section abuffer

Buffer audio frames, and make them available to the filter chain.

This source is mainly intended for a programmatic use, in particular
through the interface defined in @file{libavfilter/asrc_abuffer.h}.

It accepts the following mandatory parameters:
@var{sample_rate}:@var{sample_fmt}:@var{channel_layout}

@table @option

@item sample_rate
The sample rate of the incoming audio buffers.

@item sample_fmt
The sample format of the incoming audio buffers.
Either a sample format name or its corresponging integer representation from
the enum AVSampleFormat in @file{libavutil/samplefmt.h}

@item channel_layout
The channel layout of the incoming audio buffers.
Either a channel layout name from channel_layout_map in
@file{libavutil/audioconvert.c} or its corresponding integer representation
from the AV_CH_LAYOUT_* macros in @file{libavutil/audioconvert.h}

@end table

For example:
@example
abuffer=44100:s16p:stereo
@end example

will instruct the source to accept planar 16bit signed stereo at 44100Hz.
Since the sample format with name "s16p" corresponds to the number
6 and the "stereo" channel layout corresponds to the value 0x3, this is
equivalent to:
@example
abuffer=44100:6:0x3
@end example

@section aevalsrc

Generate an audio signal specified by an expression.

This source accepts in input one or more expressions (one for each
channel), which are evaluated and used to generate a corresponding
audio signal.

It accepts the syntax: @var{exprs}[::@var{options}].
@var{exprs} is a list of expressions separated by ":", one for each
separate channel. In case the @var{channel_layout} is not
specified, the selected channel layout depends on the number of
provided expressions.

@var{options} is an optional sequence of @var{key}=@var{value} pairs,
separated by ":".

The description of the accepted options follows.

@table @option

@item channel_layout, c
Set the channel layout. The number of channels in the specified layout
must be equal to the number of specified expressions.

@item duration, d
Set the minimum duration of the sourced audio. See the function
@code{av_parse_time()} for the accepted format.
Note that the resulting duration may be greater than the specified
duration, as the generated audio is always cut at the end of a
complete frame.

If not specified, or the expressed duration is negative, the audio is
supposed to be generated forever.

@item nb_samples, n
Set the number of samples per channel per each output frame,
default to 1024.

@item sample_rate, s
Specify the sample rate, default to 44100.
@end table

Each expression in @var{exprs} can contain the following constants:

@table @option
@item n
number of the evaluated sample, starting from 0

@item t
time of the evaluated sample expressed in seconds, starting from 0

@item s
sample rate

@end table

@subsection Examples

@itemize

@item
Generate silence:
@example
aevalsrc=0
@end example

@item

Generate a sin signal with frequency of 440 Hz, set sample rate to
8000 Hz:
@example
aevalsrc="sin(440*2*PI*t)::s=8000"
@end example

@item
Generate a two channels signal, specify the channel layout (Front
Center + Back Center) explicitly:
@example
aevalsrc="sin(420*2*PI*t):cos(430*2*PI*t)::c=FC|BC"
@end example

@item
Generate white noise:
@example
aevalsrc="-2+random(0)"
@end example

@item
Generate an amplitude modulated signal:
@example
aevalsrc="sin(10*2*PI*t)*sin(880*2*PI*t)"
@end example

@item
Generate 2.5 Hz binaural beats on a 360 Hz carrier:
@example
aevalsrc="0.1*sin(2*PI*(360-2.5/2)*t) : 0.1*sin(2*PI*(360+2.5/2)*t)"
@end example

@end itemize

@section amovie

This is the same as @ref{src_movie} source, except it selects an audio
stream by default.

@section anullsrc

Null audio source, return unprocessed audio frames. It is mainly useful
as a template and to be employed in analysis / debugging tools, or as
the source for filters which ignore the input data (for example the sox
synth filter).

It accepts an optional sequence of @var{key}=@var{value} pairs,
separated by ":".

The description of the accepted options follows.

@table @option

@item sample_rate, s
Specify the sample rate, and defaults to 44100.

@item channel_layout, cl

Specify the channel layout, and can be either an integer or a string
representing a channel layout. The default value of @var{channel_layout}
is "stereo".

Check the channel_layout_map definition in
@file{libavcodec/audioconvert.c} for the mapping between strings and
channel layout values.

@item nb_samples, n
Set the number of samples per requested frames.

@end table

Follow some examples:
@example
#  set the sample rate to 48000 Hz and the channel layout to AV_CH_LAYOUT_MONO.
anullsrc=r=48000:cl=4

# same as
anullsrc=r=48000:cl=mono
@end example

@section abuffer
Buffer audio frames, and make them available to the filter chain.

This source is not intended to be part of user-supplied graph descriptions but
for insertion by calling programs through the interface defined in
@file{libavfilter/buffersrc.h}.

It accepts the following named parameters:
@table @option

@item time_base
Timebase which will be used for timestamps of submitted frames. It must be
either a floating-point number or in @var{numerator}/@var{denominator} form.

@item sample_rate
Audio sample rate.

@item sample_fmt
Name of the sample format, as returned by @code{av_get_sample_fmt_name()}.

@item channel_layout
Channel layout of the audio data, in the form that can be accepted by
@code{av_get_channel_layout()}.
@end table

All the parameters need to be explicitly defined.

@c man end AUDIO SOURCES

@chapter Audio Sinks
@c man begin AUDIO SINKS

Below is a description of the currently available audio sinks.

@section abuffersink

Buffer audio frames, and make them available to the end of filter chain.

This sink is mainly intended for programmatic use, in particular
through the interface defined in @file{libavfilter/buffersink.h}.

It requires a pointer to an AVABufferSinkContext structure, which
defines the incoming buffers' formats, to be passed as the opaque
parameter to @code{avfilter_init_filter} for initialization.

@section anullsink

Null audio sink, do absolutely nothing with the input audio. It is
mainly useful as a template and to be employed in analysis / debugging
tools.

@section abuffersink
This sink is intended for programmatic use. Frames that arrive on this sink can
be retrieved by the calling program using the interface defined in
@file{libavfilter/buffersink.h}.

This filter accepts no parameters.

@c man end AUDIO SINKS

@chapter Video Filters
@c man begin VIDEO FILTERS

When you configure your FFmpeg build, you can disable any of the
existing filters using @code{--disable-filters}.
The configure output will show the video filters included in your
build.

Below is a description of the currently available video filters.

@section alphaextract

Extract the alpha component from the input as a grayscale video. This
is especially useful with the @var{alphamerge} filter.

@section alphamerge

Add or replace the alpha component of the primary input with the
grayscale value of a second input. This is intended for use with
@var{alphaextract} to allow the transmission or storage of frame
sequences that have alpha in a format that doesn't support an alpha
channel.

For example, to reconstruct full frames from a normal YUV-encoded video
and a separate video created with @var{alphaextract}, you might use:
@example
movie=in_alpha.mkv [alpha]; [in][alpha] alphamerge [out]
@end example

Since this filter is designed for reconstruction, it operates on frame
sequences without considering timestamps, and terminates when either
input reaches end of stream. This will cause problems if your encoding
pipeline drops frames. If you're trying to apply an image as an
overlay to a video stream, consider the @var{overlay} filter instead.

@section ass

Draw ASS (Advanced Substation Alpha) subtitles on top of input video
using the libass library.

To enable compilation of this filter you need to configure FFmpeg with
@code{--enable-libass}.

This filter accepts the syntax: @var{ass_filename}[:@var{options}],
where @var{ass_filename} is the filename of the ASS file to read, and
@var{options} is an optional sequence of @var{key}=@var{value} pairs,
separated by ":".

A description of the accepted options follows.

@table @option
@item original_size
Specifies the size of the original video, the video for which the ASS file
was composed. Due to a misdesign in ASS aspect ratio arithmetic, this is
necessary to correctly scale the fonts if the aspect ratio has been changed.
@end table

For example, to render the file @file{sub.ass} on top of the input
video, use the command:
@example
ass=sub.ass
@end example

@section bbox

Compute the bounding box for the non-black pixels in the input frame
luminance plane.

This filter computes the bounding box containing all the pixels with a
luminance value greater than the minimum allowed value.
The parameters describing the bounding box are printed on the filter
log.

@section blackdetect

Detect video intervals that are (almost) completely black. Can be
useful to detect chapter transitions, commercials, or invalid
recordings. Output lines contains the time for the start, end and
duration of the detected black interval expressed in seconds.

In order to display the output lines, you need to set the loglevel at
least to the AV_LOG_INFO value.

This filter accepts a list of options in the form of
@var{key}=@var{value} pairs separated by ":". A description of the
accepted options follows.

@table @option
@item black_min_duration, d
Set the minimum detected black duration expressed in seconds. It must
be a non-negative floating point number.

Default value is 2.0.

@item picture_black_ratio_th, pic_th
Set the threshold for considering a picture "black".
Express the minimum value for the ratio:
@example
@var{nb_black_pixels} / @var{nb_pixels}
@end example

for which a picture is considered black.
Default value is 0.98.

@item pixel_black_th, pix_th
Set the threshold for considering a pixel "black".

The threshold expresses the maximum pixel luminance value for which a
pixel is considered "black". The provided value is scaled according to
the following equation:
@example
@var{absolute_threshold} = @var{luminance_minimum_value} + @var{pixel_black_th} * @var{luminance_range_size}
@end example

@var{luminance_range_size} and @var{luminance_minimum_value} depend on
the input video format, the range is [0-255] for YUV full-range
formats and [16-235] for YUV non full-range formats.

Default value is 0.10.
@end table

The following example sets the maximum pixel threshold to the minimum
value, and detects only black intervals of 2 or more seconds:
@example
blackdetect=d=2:pix_th=0.00
@end example

@section blackframe

Detect frames that are (almost) completely black. Can be useful to
detect chapter transitions or commercials. Output lines consist of
the frame number of the detected frame, the percentage of blackness,
the position in the file if known or -1 and the timestamp in seconds.

In order to display the output lines, you need to set the loglevel at
least to the AV_LOG_INFO value.

The filter accepts the syntax:
@example
blackframe[=@var{amount}:[@var{threshold}]]
@end example

@var{amount} is the percentage of the pixels that have to be below the
threshold, and defaults to 98.

@var{threshold} is the threshold below which a pixel value is
considered black, and defaults to 32.

@section boxblur

Apply boxblur algorithm to the input video.

This filter accepts the parameters:
@var{luma_radius}:@var{luma_power}:@var{chroma_radius}:@var{chroma_power}:@var{alpha_radius}:@var{alpha_power}

Chroma and alpha parameters are optional, if not specified they default
to the corresponding values set for @var{luma_radius} and
@var{luma_power}.

@var{luma_radius}, @var{chroma_radius}, and @var{alpha_radius} represent
the radius in pixels of the box used for blurring the corresponding
input plane. They are expressions, and can contain the following
constants:
@table @option
@item w, h
the input width and height in pixels

@item cw, ch
the input chroma image width and height in pixels

@item hsub, vsub
horizontal and vertical chroma subsample values. For example for the
pixel format "yuv422p" @var{hsub} is 2 and @var{vsub} is 1.
@end table

The radius must be a non-negative number, and must not be greater than
the value of the expression @code{min(w,h)/2} for the luma and alpha planes,
and of @code{min(cw,ch)/2} for the chroma planes.

@var{luma_power}, @var{chroma_power}, and @var{alpha_power} represent
how many times the boxblur filter is applied to the corresponding
plane.

Some examples follow:

@itemize

@item
Apply a boxblur filter with luma, chroma, and alpha radius
set to 2:
@example
boxblur=2:1
@end example

@item
Set luma radius to 2, alpha and chroma radius to 0
@example
boxblur=2:1:0:0:0:0
@end example

@item
Set luma and chroma radius to a fraction of the video dimension
@example
boxblur=min(h\,w)/10:1:min(cw\,ch)/10:1
@end example

@end itemize

@section colormatrix

The colormatrix filter allows conversion between any of the following color
space: BT.709 (@var{bt709}), BT.601 (@var{bt601}), SMPTE-240M (@var{smpte240m})
and FCC (@var{fcc}).

The syntax of the parameters is @var{source}:@var{destination}:

@example
colormatrix=bt601:smpte240m
@end example

@section copy

Copy the input source unchanged to the output. Mainly useful for
testing purposes.

@section crop

Crop the input video to @var{out_w}:@var{out_h}:@var{x}:@var{y}:@var{keep_aspect}

The @var{keep_aspect} parameter is optional, if specified and set to a
non-zero value will force the output display aspect ratio to be the
same of the input, by changing the output sample aspect ratio.

The @var{out_w}, @var{out_h}, @var{x}, @var{y} parameters are
expressions containing the following constants:

@table @option
@item x, y
the computed values for @var{x} and @var{y}. They are evaluated for
each new frame.

@item in_w, in_h
the input width and height

@item iw, ih
same as @var{in_w} and @var{in_h}

@item out_w, out_h
the output (cropped) width and height

@item ow, oh
same as @var{out_w} and @var{out_h}

@item a
same as @var{iw} / @var{ih}

@item sar
input sample aspect ratio

@item dar
input display aspect ratio, it is the same as (@var{iw} / @var{ih}) * @var{sar}

@item hsub, vsub
horizontal and vertical chroma subsample values. For example for the
pixel format "yuv422p" @var{hsub} is 2 and @var{vsub} is 1.

@item n
the number of input frame, starting from 0

@item pos
the position in the file of the input frame, NAN if unknown

@item t
timestamp expressed in seconds, NAN if the input timestamp is unknown

@end table

The @var{out_w} and @var{out_h} parameters specify the expressions for
the width and height of the output (cropped) video. They are
evaluated just at the configuration of the filter.

The default value of @var{out_w} is "in_w", and the default value of
@var{out_h} is "in_h".

The expression for @var{out_w} may depend on the value of @var{out_h},
and the expression for @var{out_h} may depend on @var{out_w}, but they
cannot depend on @var{x} and @var{y}, as @var{x} and @var{y} are
evaluated after @var{out_w} and @var{out_h}.

The @var{x} and @var{y} parameters specify the expressions for the
position of the top-left corner of the output (non-cropped) area. They
are evaluated for each frame. If the evaluated value is not valid, it
is approximated to the nearest valid value.

The default value of @var{x} is "(in_w-out_w)/2", and the default
value for @var{y} is "(in_h-out_h)/2", which set the cropped area at
the center of the input image.

The expression for @var{x} may depend on @var{y}, and the expression
for @var{y} may depend on @var{x}.

Follow some examples:
@example
# crop the central input area with size 100x100
crop=100:100

# crop the central input area with size 2/3 of the input video
"crop=2/3*in_w:2/3*in_h"

# crop the input video central square
crop=in_h

# delimit the rectangle with the top-left corner placed at position
# 100:100 and the right-bottom corner corresponding to the right-bottom
# corner of the input image.
crop=in_w-100:in_h-100:100:100

# crop 10 pixels from the left and right borders, and 20 pixels from
# the top and bottom borders
"crop=in_w-2*10:in_h-2*20"

# keep only the bottom right quarter of the input image
"crop=in_w/2:in_h/2:in_w/2:in_h/2"

# crop height for getting Greek harmony
"crop=in_w:1/PHI*in_w"

# trembling effect
"crop=in_w/2:in_h/2:(in_w-out_w)/2+((in_w-out_w)/2)*sin(n/10):(in_h-out_h)/2 +((in_h-out_h)/2)*sin(n/7)"

# erratic camera effect depending on timestamp
"crop=in_w/2:in_h/2:(in_w-out_w)/2+((in_w-out_w)/2)*sin(t*10):(in_h-out_h)/2 +((in_h-out_h)/2)*sin(t*13)"

# set x depending on the value of y
"crop=in_w/2:in_h/2:y:10+10*sin(n/10)"
@end example

@section cropdetect

Auto-detect crop size.

Calculate necessary cropping parameters and prints the recommended
parameters through the logging system. The detected dimensions
correspond to the non-black area of the input video.

It accepts the syntax:
@example
cropdetect[=@var{limit}[:@var{round}[:@var{reset}]]]
@end example

@table @option

@item limit
Threshold, which can be optionally specified from nothing (0) to
everything (255), defaults to 24.

@item round
Value which the width/height should be divisible by, defaults to
16. The offset is automatically adjusted to center the video. Use 2 to
get only even dimensions (needed for 4:2:2 video). 16 is best when
encoding to most video codecs.

@item reset
Counter that determines after how many frames cropdetect will reset
the previously detected largest video area and start over to detect
the current optimal crop area. Defaults to 0.

This can be useful when channel logos distort the video area. 0
indicates never reset and return the largest area encountered during
playback.
@end table

@section delogo

Suppress a TV station logo by a simple interpolation of the surrounding
pixels. Just set a rectangle covering the logo and watch it disappear
(and sometimes something even uglier appear - your mileage may vary).

The filter accepts parameters as a string of the form
"@var{x}:@var{y}:@var{w}:@var{h}:@var{band}", or as a list of
@var{key}=@var{value} pairs, separated by ":".

The description of the accepted parameters follows.

@table @option

@item x, y
Specify the top left corner coordinates of the logo. They must be
specified.

@item w, h
Specify the width and height of the logo to clear. They must be
specified.

@item band, t
Specify the thickness of the fuzzy edge of the rectangle (added to
@var{w} and @var{h}). The default value is 4.

@item show
When set to 1, a green rectangle is drawn on the screen to simplify
finding the right @var{x}, @var{y}, @var{w}, @var{h} parameters, and
@var{band} is set to 4. The default value is 0.

@end table

Some examples follow.

@itemize

@item
Set a rectangle covering the area with top left corner coordinates 0,0
and size 100x77, setting a band of size 10:
@example
delogo=0:0:100:77:10
@end example

@item
As the previous example, but use named options:
@example
delogo=x=0:y=0:w=100:h=77:band=10
@end example

@end itemize

@section deshake

Attempt to fix small changes in horizontal and/or vertical shift. This
filter helps remove camera shake from hand-holding a camera, bumping a
tripod, moving on a vehicle, etc.

The filter accepts parameters as a string of the form
"@var{x}:@var{y}:@var{w}:@var{h}:@var{rx}:@var{ry}:@var{edge}:@var{blocksize}:@var{contrast}:@var{search}:@var{filename}"

A description of the accepted parameters follows.

@table @option

@item x, y, w, h
Specify a rectangular area where to limit the search for motion
vectors.
If desired the search for motion vectors can be limited to a
rectangular area of the frame defined by its top left corner, width
and height. These parameters have the same meaning as the drawbox
filter which can be used to visualise the position of the bounding
box.

This is useful when simultaneous movement of subjects within the frame
might be confused for camera motion by the motion vector search.

If any or all of @var{x}, @var{y}, @var{w} and @var{h} are set to -1
then the full frame is used. This allows later options to be set
without specifying the bounding box for the motion vector search.

Default - search the whole frame.

@item rx, ry
Specify the maximum extent of movement in x and y directions in the
range 0-64 pixels. Default 16.

@item edge
Specify how to generate pixels to fill blanks at the edge of the
frame. An integer from 0 to 3 as follows:
@table @option
@item 0
Fill zeroes at blank locations
@item 1
Original image at blank locations
@item 2
Extruded edge value at blank locations
@item 3
Mirrored edge at blank locations
@end table

The default setting is mirror edge at blank locations.

@item blocksize
Specify the blocksize to use for motion search. Range 4-128 pixels,
default 8.

@item contrast
Specify the contrast threshold for blocks. Only blocks with more than
the specified contrast (difference between darkest and lightest
pixels) will be considered. Range 1-255, default 125.

@item search
Specify the search strategy 0 = exhaustive search, 1 = less exhaustive
search. Default - exhaustive search.

@item filename
If set then a detailed log of the motion search is written to the
specified file.

@end table

@section drawbox

Draw a colored box on the input image.

It accepts the syntax:
@example
drawbox=@var{x}:@var{y}:@var{width}:@var{height}:@var{color}
@end example

@table @option

@item x, y
Specify the top left corner coordinates of the box. Default to 0.

@item width, height
Specify the width and height of the box, if 0 they are interpreted as
the input width and height. Default to 0.

@item color
Specify the color of the box to write, it can be the name of a color
(case insensitive match) or a 0xRRGGBB[AA] sequence.
@end table

Follow some examples:
@example
# draw a black box around the edge of the input image
drawbox

# draw a box with color red and an opacity of 50%
drawbox=10:20:200:60:red@@0.5"
@end example

@section drawtext

Draw text string or text from specified file on top of video using the
libfreetype library.

To enable compilation of this filter you need to configure FFmpeg with
@code{--enable-libfreetype}.

The filter also recognizes strftime() sequences in the provided text
and expands them accordingly. Check the documentation of strftime().

The filter accepts parameters as a list of @var{key}=@var{value} pairs,
separated by ":".

The description of the accepted parameters follows.

@table @option

@item box
Used to draw a box around text using background color.
Value should be either 1 (enable) or 0 (disable).
The default value of @var{box} is 0.

@item boxcolor
The color to be used for drawing box around text.
Either a string (e.g. "yellow") or in 0xRRGGBB[AA] format
(e.g. "0xff00ff"), possibly followed by an alpha specifier.
The default value of @var{boxcolor} is "white".

@item draw
Set an expression which specifies if the text should be drawn. If the
expression evaluates to 0, the text is not drawn. This is useful for
specifying that the text should be drawn only when specific conditions
are met.

Default value is "1".

See below for the list of accepted constants and functions.

@item fix_bounds
If true, check and fix text coords to avoid clipping.

@item fontcolor
The color to be used for drawing fonts.
Either a string (e.g. "red") or in 0xRRGGBB[AA] format
(e.g. "0xff000033"), possibly followed by an alpha specifier.
The default value of @var{fontcolor} is "black".

@item fontfile
The font file to be used for drawing text. Path must be included.
This parameter is mandatory.

@item fontsize
The font size to be used for drawing text.
The default value of @var{fontsize} is 16.

@item ft_load_flags
Flags to be used for loading the fonts.

The flags map the corresponding flags supported by libfreetype, and are
a combination of the following values:
@table @var
@item default
@item no_scale
@item no_hinting
@item render
@item no_bitmap
@item vertical_layout
@item force_autohint
@item crop_bitmap
@item pedantic
@item ignore_global_advance_width
@item no_recurse
@item ignore_transform
@item monochrome
@item linear_design
@item no_autohint
@item end table
@end table

Default value is "render".

For more information consult the documentation for the FT_LOAD_*
libfreetype flags.

@item shadowcolor
The color to be used for drawing a shadow behind the drawn text.  It
can be a color name (e.g. "yellow") or a string in the 0xRRGGBB[AA]
form (e.g. "0xff00ff"), possibly followed by an alpha specifier.
The default value of @var{shadowcolor} is "black".

@item shadowx, shadowy
The x and y offsets for the text shadow position with respect to the
position of the text. They can be either positive or negative
values. Default value for both is "0".

@item tabsize
The size in number of spaces to use for rendering the tab.
Default value is 4.

@item timecode
Set the initial timecode representation in "hh:mm:ss[:;.]ff"
format. It can be used with or without text parameter. @var{timecode_rate}
option must be specified.

@item timecode_rate, rate, r
Set the timecode frame rate (timecode only).

@item text
The text string to be drawn. The text must be a sequence of UTF-8
encoded characters.
This parameter is mandatory if no file is specified with the parameter
@var{textfile}.

@item textfile
A text file containing text to be drawn. The text must be a sequence
of UTF-8 encoded characters.

This parameter is mandatory if no text string is specified with the
parameter @var{text}.

If both @var{text} and @var{textfile} are specified, an error is thrown.

@item x, y
The expressions which specify the offsets where text will be drawn
within the video frame. They are relative to the top/left border of the
output image.

The default value of @var{x} and @var{y} is "0".

See below for the list of accepted constants and functions.
@end table

The parameters for @var{x} and @var{y} are expressions containing the
following constants and functions:

@table @option
@item dar
input display aspect ratio, it is the same as (@var{w} / @var{h}) * @var{sar}

@item hsub, vsub
horizontal and vertical chroma subsample values. For example for the
pixel format "yuv422p" @var{hsub} is 2 and @var{vsub} is 1.

@item line_h, lh
the height of each text line

@item main_h, h, H
the input height

@item main_w, w, W
the input width

@item max_glyph_a, ascent
the maximum distance from the baseline to the highest/upper grid
coordinate used to place a glyph outline point, for all the rendered
glyphs.
It is a positive value, due to the grid's orientation with the Y axis
upwards.

@item max_glyph_d, descent
the maximum distance from the baseline to the lowest grid coordinate
used to place a glyph outline point, for all the rendered glyphs.
This is a negative value, due to the grid's orientation, with the Y axis
upwards.

@item max_glyph_h
maximum glyph height, that is the maximum height for all the glyphs
contained in the rendered text, it is equivalent to @var{ascent} -
@var{descent}.

@item max_glyph_w
maximum glyph width, that is the maximum width for all the glyphs
contained in the rendered text

@item n
the number of input frame, starting from 0

@item rand(min, max)
return a random number included between @var{min} and @var{max}

@item sar
input sample aspect ratio

@item t
timestamp expressed in seconds, NAN if the input timestamp is unknown

@item text_h, th
the height of the rendered text

@item text_w, tw
the width of the rendered text

@item x, y
the x and y offset coordinates where the text is drawn.

These parameters allow the @var{x} and @var{y} expressions to refer
each other, so you can for example specify @code{y=x/dar}.
@end table

If libavfilter was built with @code{--enable-fontconfig}, then
@option{fontfile} can be a fontconfig pattern or omitted.

Some examples follow.

@itemize

@item
Draw "Test Text" with font FreeSerif, using the default values for the
optional parameters.

@example
drawtext="fontfile=/usr/share/fonts/truetype/freefont/FreeSerif.ttf: text='Test Text'"
@end example

@item
Draw 'Test Text' with font FreeSerif of size 24 at position x=100
and y=50 (counting from the top-left corner of the screen), text is
yellow with a red box around it. Both the text and the box have an
opacity of 20%.

@example
drawtext="fontfile=/usr/share/fonts/truetype/freefont/FreeSerif.ttf: text='Test Text':\
          x=100: y=50: fontsize=24: fontcolor=yellow@@0.2: box=1: boxcolor=red@@0.2"
@end example

Note that the double quotes are not necessary if spaces are not used
within the parameter list.

@item
Show the text at the center of the video frame:
@example
drawtext="fontsize=30:fontfile=FreeSerif.ttf:text='hello world':x=(w-text_w)/2:y=(h-text_h-line_h)/2"
@end example

@item
Show a text line sliding from right to left in the last row of the video
frame. The file @file{LONG_LINE} is assumed to contain a single line
with no newlines.
@example
drawtext="fontsize=15:fontfile=FreeSerif.ttf:text=LONG_LINE:y=h-line_h:x=-50*t"
@end example

@item
Show the content of file @file{CREDITS} off the bottom of the frame and scroll up.
@example
drawtext="fontsize=20:fontfile=FreeSerif.ttf:textfile=CREDITS:y=h-20*t"
@end example

@item
Draw a single green letter "g", at the center of the input video.
The glyph baseline is placed at half screen height.
@example
drawtext="fontsize=60:fontfile=FreeSerif.ttf:fontcolor=green:text=g:x=(w-max_glyph_w)/2:y=h/2-ascent"
@end example

@item
Show text for 1 second every 3 seconds:
@example
drawtext="fontfile=FreeSerif.ttf:fontcolor=white:x=100:y=x/dar:draw=lt(mod(t\\,3)\\,1):text='blink'"
@end example

@item
Use fontconfig to set the font. Note that the colons need to be escaped.
@example
drawtext='fontfile=Linux Libertine O-40\\:style=Semibold:text=FFmpeg'
@end example

@end itemize

For more information about libfreetype, check:
@url{http://www.freetype.org/}.

For more information about fontconfig, check:
@url{http://freedesktop.org/software/fontconfig/fontconfig-user.html}.

@section fade

Apply fade-in/out effect to input video.

It accepts the parameters:
@var{type}:@var{start_frame}:@var{nb_frames}[:@var{options}]

@var{type} specifies if the effect type, can be either "in" for
fade-in, or "out" for a fade-out effect.

@var{start_frame} specifies the number of the start frame for starting
to apply the fade effect.

@var{nb_frames} specifies the number of frames for which the fade
effect has to last. At the end of the fade-in effect the output video
will have the same intensity as the input video, at the end of the
fade-out transition the output video will be completely black.

@var{options} is an optional sequence of @var{key}=@var{value} pairs,
separated by ":". The description of the accepted options follows.

@table @option

@item type, t
See @var{type}.

@item start_frame, s
See @var{start_frame}.

@item nb_frames, n
See @var{nb_frames}.

@item alpha
If set to 1, fade only alpha channel, if one exists on the input.
Default value is 0.
@end table

A few usage examples follow, usable too as test scenarios.
@example
# fade in first 30 frames of video
fade=in:0:30

# fade out last 45 frames of a 200-frame video
fade=out:155:45

# fade in first 25 frames and fade out last 25 frames of a 1000-frame video
fade=in:0:25, fade=out:975:25

# make first 5 frames black, then fade in from frame 5-24
fade=in:5:20

# fade in alpha over first 25 frames of video
fade=in:0:25:alpha=1
@end example

@section fieldorder

Transform the field order of the input video.

It accepts one parameter which specifies the required field order that
the input interlaced video will be transformed to. The parameter can
assume one of the following values:

@table @option
@item 0 or bff
output bottom field first
@item 1 or tff
output top field first
@end table

Default value is "tff".

Transformation is achieved by shifting the picture content up or down
by one line, and filling the remaining line with appropriate picture content.
This method is consistent with most broadcast field order converters.

If the input video is not flagged as being interlaced, or it is already
flagged as being of the required output field order then this filter does
not alter the incoming video.

This filter is very useful when converting to or from PAL DV material,
which is bottom field first.

For example:
@example
ffmpeg -i in.vob -vf "fieldorder=bff" out.dv
@end example

@section fifo

Buffer input images and send them when they are requested.

This filter is mainly useful when auto-inserted by the libavfilter
framework.

The filter does not take parameters.

@section format

Convert the input video to one of the specified pixel formats.
Libavfilter will try to pick one that is supported for the input to
the next filter.

The filter accepts a list of pixel format names, separated by ":",
for example "yuv420p:monow:rgb24".

Some examples follow:
@example
# convert the input video to the format "yuv420p"
format=yuv420p

# convert the input video to any of the formats in the list
format=yuv420p:yuv444p:yuv410p
@end example

@section fps

Convert the video to specified constant framerate by duplicating or dropping
frames as necessary.

This filter accepts the following named parameters:
@table @option

@item fps
Desired output framerate.

@end table

@anchor{frei0r}
@section frei0r

Apply a frei0r effect to the input video.

To enable compilation of this filter you need to install the frei0r
header and configure FFmpeg with @code{--enable-frei0r}.

The filter supports the syntax:
@example
@var{filter_name}[@{:|=@}@var{param1}:@var{param2}:...:@var{paramN}]
@end example

@var{filter_name} is the name to the frei0r effect to load. If the
environment variable @env{FREI0R_PATH} is defined, the frei0r effect
is searched in each one of the directories specified by the colon
separated list in @env{FREIOR_PATH}, otherwise in the standard frei0r
paths, which are in this order: @file{HOME/.frei0r-1/lib/},
@file{/usr/local/lib/frei0r-1/}, @file{/usr/lib/frei0r-1/}.

@var{param1}, @var{param2}, ... , @var{paramN} specify the parameters
for the frei0r effect.

A frei0r effect parameter can be a boolean (whose values are specified
with "y" and "n"), a double, a color (specified by the syntax
@var{R}/@var{G}/@var{B}, @var{R}, @var{G}, and @var{B} being float
numbers from 0.0 to 1.0) or by an @code{av_parse_color()} color
description), a position (specified by the syntax @var{X}/@var{Y},
@var{X} and @var{Y} being float numbers) and a string.

The number and kind of parameters depend on the loaded effect. If an
effect parameter is not specified the default value is set.

Some examples follow:

@itemize
@item
Apply the distort0r effect, set the first two double parameters:
@example
frei0r=distort0r:0.5:0.01
@end example

@item
Apply the colordistance effect, takes a color as first parameter:
@example
frei0r=colordistance:0.2/0.3/0.4
frei0r=colordistance:violet
frei0r=colordistance:0x112233
@end example

@item
Apply the perspective effect, specify the top left and top right image
positions:
@example
frei0r=perspective:0.2/0.2:0.8/0.2
@end example
@end itemize

For more information see:
@url{http://frei0r.dyne.org}

@section gradfun

Fix the banding artifacts that are sometimes introduced into nearly flat
regions by truncation to 8bit color depth.
Interpolate the gradients that should go where the bands are, and
dither them.

This filter is designed for playback only.  Do not use it prior to
lossy compression, because compression tends to lose the dither and
bring back the bands.

The filter takes two optional parameters, separated by ':':
@var{strength}:@var{radius}

@var{strength} is the maximum amount by which the filter will change
any one pixel. Also the threshold for detecting nearly flat
regions. Acceptable values range from .51 to 255, default value is
1.2, out-of-range values will be clipped to the valid range.

@var{radius} is the neighborhood to fit the gradient to. A larger
radius makes for smoother gradients, but also prevents the filter from
modifying the pixels near detailed regions. Acceptable values are
8-32, default value is 16, out-of-range values will be clipped to the
valid range.

@example
# default parameters
gradfun=1.2:16

# omitting radius
gradfun=1.2
@end example

@section hflip

Flip the input video horizontally.

For example to horizontally flip the input video with @command{ffmpeg}:
@example
ffmpeg -i in.avi -vf "hflip" out.avi
@end example

@section hqdn3d

High precision/quality 3d denoise filter. This filter aims to reduce
image noise producing smooth images and making still images really
still. It should enhance compressibility.

It accepts the following optional parameters:
@var{luma_spatial}:@var{chroma_spatial}:@var{luma_tmp}:@var{chroma_tmp}

@table @option
@item luma_spatial
a non-negative float number which specifies spatial luma strength,
defaults to 4.0

@item chroma_spatial
a non-negative float number which specifies spatial chroma strength,
defaults to 3.0*@var{luma_spatial}/4.0

@item luma_tmp
a float number which specifies luma temporal strength, defaults to
6.0*@var{luma_spatial}/4.0

@item chroma_tmp
a float number which specifies chroma temporal strength, defaults to
@var{luma_tmp}*@var{chroma_spatial}/@var{luma_spatial}
@end table

@section idet

Interlaceing detect filter. This filter tries to detect if the input is
interlaced or progressive. Top or bottom field first.

@section lut, lutrgb, lutyuv

Compute a look-up table for binding each pixel component input value
to an output value, and apply it to input video.

@var{lutyuv} applies a lookup table to a YUV input video, @var{lutrgb}
to an RGB input video.

These filters accept in input a ":"-separated list of options, which
specify the expressions used for computing the lookup table for the
corresponding pixel component values.

The @var{lut} filter requires either YUV or RGB pixel formats in
input, and accepts the options:
@table @option
@item c0
first  pixel component
@item c1
second pixel component
@item c2
third  pixel component
@item c3
fourth pixel component, corresponds to the alpha component
@end table

The exact component associated to each option depends on the format in
input.

The @var{lutrgb} filter requires RGB pixel formats in input, and
accepts the options:
@table @option
@item r
red component
@item g
green component
@item b
blue component
@item a
alpha component
@end table

The @var{lutyuv} filter requires YUV pixel formats in input, and
accepts the options:
@table @option
@item y
Y/luminance component
@item u
U/Cb component
@item v
V/Cr component
@item a
alpha component
@end table

The expressions can contain the following constants and functions:

@table @option
@item w, h
the input width and height

@item val
input value for the pixel component

@item clipval
the input value clipped in the @var{minval}-@var{maxval} range

@item maxval
maximum value for the pixel component

@item minval
minimum value for the pixel component

@item negval
the negated value for the pixel component value clipped in the
@var{minval}-@var{maxval} range , it corresponds to the expression
"maxval-clipval+minval"

@item clip(val)
the computed value in @var{val} clipped in the
@var{minval}-@var{maxval} range

@item gammaval(gamma)
the computed gamma correction value of the pixel component value
clipped in the @var{minval}-@var{maxval} range, corresponds to the
expression
"pow((clipval-minval)/(maxval-minval)\,@var{gamma})*(maxval-minval)+minval"

@end table

All expressions default to "val".

Some examples follow:
@example
# negate input video
lutrgb="r=maxval+minval-val:g=maxval+minval-val:b=maxval+minval-val"
lutyuv="y=maxval+minval-val:u=maxval+minval-val:v=maxval+minval-val"

# the above is the same as
lutrgb="r=negval:g=negval:b=negval"
lutyuv="y=negval:u=negval:v=negval"

# negate luminance
lutyuv=y=negval

# remove chroma components, turns the video into a graytone image
lutyuv="u=128:v=128"

# apply a luma burning effect
lutyuv="y=2*val"

# remove green and blue components
lutrgb="g=0:b=0"

# set a constant alpha channel value on input
format=rgba,lutrgb=a="maxval-minval/2"

# correct luminance gamma by a 0.5 factor
lutyuv=y=gammaval(0.5)
@end example

@section mp

Apply an MPlayer filter to the input video.

This filter provides a wrapper around most of the filters of
MPlayer/MEncoder.

This wrapper is considered experimental. Some of the wrapped filters
may not work properly and we may drop support for them, as they will
be implemented natively into FFmpeg. Thus you should avoid
depending on them when writing portable scripts.

The filters accepts the parameters:
@var{filter_name}[:=]@var{filter_params}

@var{filter_name} is the name of a supported MPlayer filter,
@var{filter_params} is a string containing the parameters accepted by
the named filter.

The list of the currently supported filters follows:
@table @var
@item decimate
@item denoise3d
@item detc
@item dint
@item divtc
@item down3dright
@item dsize
@item eq2
@item eq
@item field
@item fil
@item fixpts
@item framestep
@item fspp
@item geq
@item harddup
@item hqdn3d
@item hue
@item il
@item ilpack
@item ivtc
@item kerndeint
@item mcdeint
@item noise
@item ow
@item palette
@item perspective
@item phase
@item pp7
@item pullup
@item qp
@item rectangle
@item rotate
@item sab
@item smartblur
@item softpulldown
@item softskip
@item spp
@item telecine
@item tile
@item tinterlace
@item unsharp
@item uspp
@item yuvcsp
@item yvu9
@end table

The parameter syntax and behavior for the listed filters are the same
of the corresponding MPlayer filters. For detailed instructions check
the "VIDEO FILTERS" section in the MPlayer manual.

Some examples follow:
@example
# adjust gamma, brightness, contrast
mp=eq2=1.0:2:0.5

# tweak hue and saturation
mp=hue=100:-10
@end example

See also mplayer(1), @url{http://www.mplayerhq.hu/}.

@section negate

Negate input video.

This filter accepts an integer in input, if non-zero it negates the
alpha component (if available). The default value in input is 0.

@section noformat

Force libavfilter not to use any of the specified pixel formats for the
input to the next filter.

The filter accepts a list of pixel format names, separated by ":",
for example "yuv420p:monow:rgb24".

Some examples follow:
@example
# force libavfilter to use a format different from "yuv420p" for the
# input to the vflip filter
noformat=yuv420p,vflip

# convert the input video to any of the formats not contained in the list
noformat=yuv420p:yuv444p:yuv410p
@end example

@section null

Pass the video source unchanged to the output.

@section ocv

Apply video transform using libopencv.

To enable this filter install libopencv library and headers and
configure FFmpeg with @code{--enable-libopencv}.

The filter takes the parameters: @var{filter_name}@{:=@}@var{filter_params}.

@var{filter_name} is the name of the libopencv filter to apply.

@var{filter_params} specifies the parameters to pass to the libopencv
filter. If not specified the default values are assumed.

Refer to the official libopencv documentation for more precise
information:
@url{http://opencv.willowgarage.com/documentation/c/image_filtering.html}

Follows the list of supported libopencv filters.

@anchor{dilate}
@subsection dilate

Dilate an image by using a specific structuring element.
This filter corresponds to the libopencv function @code{cvDilate}.

It accepts the parameters: @var{struct_el}:@var{nb_iterations}.

@var{struct_el} represents a structuring element, and has the syntax:
@var{cols}x@var{rows}+@var{anchor_x}x@var{anchor_y}/@var{shape}

@var{cols} and @var{rows} represent the number of columns and rows of
the structuring element, @var{anchor_x} and @var{anchor_y} the anchor
point, and @var{shape} the shape for the structuring element, and
can be one of the values "rect", "cross", "ellipse", "custom".

If the value for @var{shape} is "custom", it must be followed by a
string of the form "=@var{filename}". The file with name
@var{filename} is assumed to represent a binary image, with each
printable character corresponding to a bright pixel. When a custom
@var{shape} is used, @var{cols} and @var{rows} are ignored, the number
or columns and rows of the read file are assumed instead.

The default value for @var{struct_el} is "3x3+0x0/rect".

@var{nb_iterations} specifies the number of times the transform is
applied to the image, and defaults to 1.

Follow some example:
@example
# use the default values
ocv=dilate

# dilate using a structuring element with a 5x5 cross, iterate two times
ocv=dilate=5x5+2x2/cross:2

# read the shape from the file diamond.shape, iterate two times
# the file diamond.shape may contain a pattern of characters like this:
#   *
#  ***
# *****
#  ***
#   *
# the specified cols and rows are ignored (but not the anchor point coordinates)
ocv=0x0+2x2/custom=diamond.shape:2
@end example

@subsection erode

Erode an image by using a specific structuring element.
This filter corresponds to the libopencv function @code{cvErode}.

The filter accepts the parameters: @var{struct_el}:@var{nb_iterations},
with the same syntax and semantics as the @ref{dilate} filter.

@subsection smooth

Smooth the input video.

The filter takes the following parameters:
@var{type}:@var{param1}:@var{param2}:@var{param3}:@var{param4}.

@var{type} is the type of smooth filter to apply, and can be one of
the following values: "blur", "blur_no_scale", "median", "gaussian",
"bilateral". The default value is "gaussian".

@var{param1}, @var{param2}, @var{param3}, and @var{param4} are
parameters whose meanings depend on smooth type. @var{param1} and
@var{param2} accept integer positive values or 0, @var{param3} and
@var{param4} accept float values.

The default value for @var{param1} is 3, the default value for the
other parameters is 0.

These parameters correspond to the parameters assigned to the
libopencv function @code{cvSmooth}.

@anchor{overlay}
@section overlay

Overlay one video on top of another.

It takes two inputs and one output, the first input is the "main"
video on which the second input is overlayed.

It accepts the parameters: @var{x}:@var{y}[:@var{options}].

@var{x} is the x coordinate of the overlayed video on the main video,
@var{y} is the y coordinate. @var{x} and @var{y} are expressions containing
the following parameters:

@table @option
@item main_w, main_h
main input width and height

@item W, H
same as @var{main_w} and @var{main_h}

@item overlay_w, overlay_h
overlay input width and height

@item w, h
same as @var{overlay_w} and @var{overlay_h}
@end table

@var{options} is an optional list of @var{key}=@var{value} pairs,
separated by ":".

The description of the accepted options follows.

@table @option
@item rgb
If set to 1, force the filter to accept inputs in the RGB
color space. Default value is 0.
@end table

Be aware that frames are taken from each input video in timestamp
order, hence, if their initial timestamps differ, it is a a good idea
to pass the two inputs through a @var{setpts=PTS-STARTPTS} filter to
have them begin in the same zero timestamp, as it does the example for
the @var{movie} filter.

Follow some examples:
@example
# draw the overlay at 10 pixels from the bottom right
# corner of the main video.
overlay=main_w-overlay_w-10:main_h-overlay_h-10

# insert a transparent PNG logo in the bottom left corner of the input
ffmpeg -i input -i logo -filter_complex 'overlay=10:main_h-overlay_h-10' output

# insert 2 different transparent PNG logos (second logo on bottom
# right corner):
ffmpeg -i input -i logo1 -i logo2 -filter_complex
'overlay=10:H-h-10,overlay=W-w-10:H-h-10' output

# add a transparent color layer on top of the main video,
# WxH specifies the size of the main input to the overlay filter
color=red@.3:WxH [over]; [in][over] overlay [out]

# play an original video and a filtered version (here with the deshake filter)
# side by side
ffplay input.avi -vf 'split[a][b]; [a]pad=iw*2:ih[src]; [b]deshake[filt]; [src][filt]overlay=w'

# the previous example is the same as:
ffplay input.avi -vf 'split[b], pad=iw*2[src], [b]deshake, [src]overlay=w'
@end example

You can chain together more overlays but the efficiency of such
approach is yet to be tested.

@section pad

Add paddings to the input image, and places the original input at the
given coordinates @var{x}, @var{y}.

It accepts the following parameters:
@var{width}:@var{height}:@var{x}:@var{y}:@var{color}.

The parameters @var{width}, @var{height}, @var{x}, and @var{y} are
expressions containing the following constants:

@table @option
@item in_w, in_h
the input video width and height

@item iw, ih
same as @var{in_w} and @var{in_h}

@item out_w, out_h
the output width and height, that is the size of the padded area as
specified by the @var{width} and @var{height} expressions

@item ow, oh
same as @var{out_w} and @var{out_h}

@item x, y
x and y offsets as specified by the @var{x} and @var{y}
expressions, or NAN if not yet specified

@item a
same as @var{iw} / @var{ih}

@item sar
input sample aspect ratio

@item dar
input display aspect ratio, it is the same as (@var{iw} / @var{ih}) * @var{sar}

@item hsub, vsub
horizontal and vertical chroma subsample values. For example for the
pixel format "yuv422p" @var{hsub} is 2 and @var{vsub} is 1.
@end table

Follows the description of the accepted parameters.

@table @option
@item width, height

Specify the size of the output image with the paddings added. If the
value for @var{width} or @var{height} is 0, the corresponding input size
is used for the output.

The @var{width} expression can reference the value set by the
@var{height} expression, and vice versa.

The default value of @var{width} and @var{height} is 0.

@item x, y

Specify the offsets where to place the input image in the padded area
with respect to the top/left border of the output image.

The @var{x} expression can reference the value set by the @var{y}
expression, and vice versa.

The default value of @var{x} and @var{y} is 0.

@item color

Specify the color of the padded area, it can be the name of a color
(case insensitive match) or a 0xRRGGBB[AA] sequence.

The default value of @var{color} is "black".

@end table

Some examples follow:

@example
# Add paddings with color "violet" to the input video. Output video
# size is 640x480, the top-left corner of the input video is placed at
# column 0, row 40.
pad=640:480:0:40:violet

# pad the input to get an output with dimensions increased bt 3/2,
# and put the input video at the center of the padded area
pad="3/2*iw:3/2*ih:(ow-iw)/2:(oh-ih)/2"

# pad the input to get a squared output with size equal to the maximum
# value between the input width and height, and put the input video at
# the center of the padded area
pad="max(iw\,ih):ow:(ow-iw)/2:(oh-ih)/2"

# pad the input to get a final w/h ratio of 16:9
pad="ih*16/9:ih:(ow-iw)/2:(oh-ih)/2"

# for anamorphic video, in order to set the output display aspect ratio,
# it is necessary to use sar in the expression, according to the relation:
# (ih * X / ih) * sar = output_dar
# X = output_dar / sar
pad="ih*16/9/sar:ih:(ow-iw)/2:(oh-ih)/2"

# double output size and put the input video in the bottom-right
# corner of the output padded area
pad="2*iw:2*ih:ow-iw:oh-ih"
@end example

@section pixdesctest

Pixel format descriptor test filter, mainly useful for internal
testing. The output video should be equal to the input video.

For example:
@example
format=monow, pixdesctest
@end example

can be used to test the monowhite pixel format descriptor definition.

@section removelogo

Suppress a TV station logo, using an image file to determine which
pixels comprise the logo. It works by filling in the pixels that
comprise the logo with neighboring pixels.

This filter requires one argument which specifies the filter bitmap
file, which can be any image format supported by libavformat. The
width and height of the image file must match those of the video
stream being processed.

Pixels in the provided bitmap image with a value of zero are not
considered part of the logo, non-zero pixels are considered part of
the logo. If you use white (255) for the logo and black (0) for the
rest, you will be safe. For making the filter bitmap, it is
recommended to take a screen capture of a black frame with the logo
visible, and then using a threshold filter followed by the erode
filter once or twice.

If needed, little splotches can be fixed manually. Remember that if
logo pixels are not covered, the filter quality will be much
reduced. Marking too many pixels as part of the logo does not hurt as
much, but it will increase the amount of blurring needed to cover over
the image and will destroy more information than necessary, and extra
pixels will slow things down on a large logo.

@section scale

Scale the input video to @var{width}:@var{height}[:@var{interl}=@{1|-1@}] and/or convert the image format.

The scale filter forces the output display aspect ratio to be the same
of the input, by changing the output sample aspect ratio.

The parameters @var{width} and @var{height} are expressions containing
the following constants:

@table @option
@item in_w, in_h
the input width and height

@item iw, ih
same as @var{in_w} and @var{in_h}

@item out_w, out_h
the output (cropped) width and height

@item ow, oh
same as @var{out_w} and @var{out_h}

@item a
same as @var{iw} / @var{ih}

@item sar
input sample aspect ratio

@item dar
input display aspect ratio, it is the same as (@var{iw} / @var{ih}) * @var{sar}

@item hsub, vsub
horizontal and vertical chroma subsample values. For example for the
pixel format "yuv422p" @var{hsub} is 2 and @var{vsub} is 1.
@end table

If the input image format is different from the format requested by
the next filter, the scale filter will convert the input to the
requested format.

If the value for @var{width} or @var{height} is 0, the respective input
size is used for the output.

If the value for @var{width} or @var{height} is -1, the scale filter will
use, for the respective output size, a value that maintains the aspect
ratio of the input image.

The default value of @var{width} and @var{height} is 0.

Valid values for the optional parameter @var{interl} are:

@table @option
@item 1
force interlaced aware scaling

@item -1
select interlaced aware scaling depending on whether the source frames
are flagged as interlaced or not
@end table

Unless @var{interl} is set to one of the above options, interlaced scaling will not be used.

Some examples follow:
@example
# scale the input video to a size of 200x100.
scale=200:100

# scale the input to 2x
scale=2*iw:2*ih
# the above is the same as
scale=2*in_w:2*in_h

# scale the input to 2x with forced interlaced scaling
scale=2*iw:2*ih:interl=1

# scale the input to half size
scale=iw/2:ih/2

# increase the width, and set the height to the same size
scale=3/2*iw:ow

# seek for Greek harmony
scale=iw:1/PHI*iw
scale=ih*PHI:ih

# increase the height, and set the width to 3/2 of the height
scale=3/2*oh:3/5*ih

# increase the size, but make the size a multiple of the chroma
scale="trunc(3/2*iw/hsub)*hsub:trunc(3/2*ih/vsub)*vsub"

# increase the width to a maximum of 500 pixels, keep the same input aspect ratio
scale='min(500\, iw*3/2):-1'
@end example

@section select
Select frames to pass in output.

It accepts in input an expression, which is evaluated for each input
frame. If the expression is evaluated to a non-zero value, the frame
is selected and passed to the output, otherwise it is discarded.

The expression can contain the following constants:

@table @option
@item n
the sequential number of the filtered frame, starting from 0

@item selected_n
the sequential number of the selected frame, starting from 0

@item prev_selected_n
the sequential number of the last selected frame, NAN if undefined

@item TB
timebase of the input timestamps

@item pts
the PTS (Presentation TimeStamp) of the filtered video frame,
expressed in @var{TB} units, NAN if undefined

@item t
the PTS (Presentation TimeStamp) of the filtered video frame,
expressed in seconds, NAN if undefined

@item prev_pts
the PTS of the previously filtered video frame, NAN if undefined

@item prev_selected_pts
the PTS of the last previously filtered video frame, NAN if undefined

@item prev_selected_t
the PTS of the last previously selected video frame, NAN if undefined

@item start_pts
the PTS of the first video frame in the video, NAN if undefined

@item start_t
the time of the first video frame in the video, NAN if undefined

@item pict_type
the type of the filtered frame, can assume one of the following
values:
@table @option
@item I
@item P
@item B
@item S
@item SI
@item SP
@item BI
@end table

@item interlace_type
the frame interlace type, can assume one of the following values:
@table @option
@item PROGRESSIVE
the frame is progressive (not interlaced)
@item TOPFIRST
the frame is top-field-first
@item BOTTOMFIRST
the frame is bottom-field-first
@end table

@item key
1 if the filtered frame is a key-frame, 0 otherwise

@item pos
the position in the file of the filtered frame, -1 if the information
is not available (e.g. for synthetic video)

@item scene
value between 0 and 1 to indicate a new scene; a low value reflects a low
probability for the current frame to introduce a new scene, while a higher
value means the current frame is more likely to be one (see the example below)

@end table

The default value of the select expression is "1".

Some examples follow:

@example
# select all frames in input
select

# the above is the same as:
select=1

# skip all frames:
select=0

# select only I-frames
select='eq(pict_type\,I)'

# select one frame every 100
select='not(mod(n\,100))'

# select only frames contained in the 10-20 time interval
select='gte(t\,10)*lte(t\,20)'

# select only I frames contained in the 10-20 time interval
select='gte(t\,10)*lte(t\,20)*eq(pict_type\,I)'

# select frames with a minimum distance of 10 seconds
select='isnan(prev_selected_t)+gte(t-prev_selected_t\,10)'
@end example

Complete example to create a mosaic of the first scenes:

@example
ffmpeg -i video.avi -vf select='gt(scene\,0.4)',scale=160:120,tile -frames:v 1 preview.png
@end example

Comparing @var{scene} against a value between 0.3 and 0.5 is generally a sane
choice.

@section setdar, setsar

The @code{setdar} filter sets the Display Aspect Ratio for the filter
output video.

This is done by changing the specified Sample (aka Pixel) Aspect
Ratio, according to the following equation:
@example
@var{DAR} = @var{HORIZONTAL_RESOLUTION} / @var{VERTICAL_RESOLUTION} * @var{SAR}
@end example

Keep in mind that the @code{setdar} filter does not modify the pixel
dimensions of the video frame. Also the display aspect ratio set by
this filter may be changed by later filters in the filterchain,
e.g. in case of scaling or if another "setdar" or a "setsar" filter is
applied.

The @code{setsar} filter sets the Sample (aka Pixel) Aspect Ratio for
the filter output video.

Note that as a consequence of the application of this filter, the
output display aspect ratio will change according to the equation
above.

Keep in mind that the sample aspect ratio set by the @code{setsar}
filter may be changed by later filters in the filterchain, e.g. if
another "setsar" or a "setdar" filter is applied.

The @code{setdar} and @code{setsar} filters accept a parameter string
which represents the wanted aspect ratio.  The parameter can
be a floating point number string, an expression, or a string of the form
@var{num}:@var{den}, where @var{num} and @var{den} are the numerator
and denominator of the aspect ratio. If the parameter is not
specified, it is assumed the value "0:1".

For example to change the display aspect ratio to 16:9, specify:
@example
setdar=16:9
@end example

The example above is equivalent to:
@example
setdar=1.77777
@end example

To change the sample aspect ratio to 10:11, specify:
@example
setsar=10:11
@end example

@section setfield

Force field for the output video frame.

The @code{setfield} filter marks the interlace type field for the
output frames. It does not change the input frame, but only sets the
corresponding property, which affects how the frame is treated by
following filters (e.g. @code{fieldorder} or @code{yadif}).

It accepts a string parameter, which can assume the following values:
@table @samp
@item auto
Keep the same field property.

@item bff
Mark the frame as bottom-field-first.

@item tff
Mark the frame as top-field-first.

@item prog
Mark the frame as progressive.
@end table

@section setpts

Change the PTS (presentation timestamp) of the input video frames.

Accept in input an expression evaluated through the eval API, which
can contain the following constants:

@table @option
@item PTS
the presentation timestamp in input

@item N
the count of the input frame, starting from 0.

@item STARTPTS
the PTS of the first video frame

@item INTERLACED
tell if the current frame is interlaced

@item POS
original position in the file of the frame, or undefined if undefined
for the current frame

@item PREV_INPTS
previous input PTS

@item PREV_OUTPTS
previous output PTS

@end table

Some examples follow:

@example
# start counting PTS from zero
setpts=PTS-STARTPTS

# fast motion
setpts=0.5*PTS

# slow motion
setpts=2.0*PTS

# fixed rate 25 fps
setpts=N/(25*TB)

# fixed rate 25 fps with some jitter
setpts='1/(25*TB) * (N + 0.05 * sin(N*2*PI/25))'
@end example

@section settb, asettb

Set the timebase to use for the output frames timestamps.
It is mainly useful for testing timebase configuration.

It accepts in input an arithmetic expression representing a rational.
The expression can contain the constants "AVTB" (the
default timebase), "intb" (the input timebase) and "sr" (the sample rate,
audio only).

The default value for the input is "intb".

Follow some examples.

@example
# set the timebase to 1/25
settb=1/25

# set the timebase to 1/10
settb=0.1

#set the timebase to 1001/1000
settb=1+0.001

#set the timebase to 2*intb
settb=2*intb

#set the default timebase value
settb=AVTB
@end example

@section showinfo

Show a line containing various information for each input video frame.
The input video is not modified.

The shown line contains a sequence of key/value pairs of the form
@var{key}:@var{value}.

A description of each shown parameter follows:

@table @option
@item n
sequential number of the input frame, starting from 0

@item pts
Presentation TimeStamp of the input frame, expressed as a number of
time base units. The time base unit depends on the filter input pad.

@item pts_time
Presentation TimeStamp of the input frame, expressed as a number of
seconds

@item pos
position of the frame in the input stream, -1 if this information in
unavailable and/or meaningless (for example in case of synthetic video)

@item fmt
pixel format name

@item sar
sample aspect ratio of the input frame, expressed in the form
@var{num}/@var{den}

@item s
size of the input frame, expressed in the form
@var{width}x@var{height}

@item i
interlaced mode ("P" for "progressive", "T" for top field first, "B"
for bottom field first)

@item iskey
1 if the frame is a key frame, 0 otherwise

@item type
picture type of the input frame ("I" for an I-frame, "P" for a
P-frame, "B" for a B-frame, "?" for unknown type).
Check also the documentation of the @code{AVPictureType} enum and of
the @code{av_get_picture_type_char} function defined in
@file{libavutil/avutil.h}.

@item checksum
Adler-32 checksum (printed in hexadecimal) of all the planes of the input frame

@item plane_checksum
Adler-32 checksum (printed in hexadecimal) of each plane of the input frame,
expressed in the form "[@var{c0} @var{c1} @var{c2} @var{c3}]"
@end table

@section slicify

Pass the images of input video on to next video filter as multiple
slices.

@example
ffmpeg -i in.avi -vf "slicify=32" out.avi
@end example

The filter accepts the slice height as parameter. If the parameter is
not specified it will use the default value of 16.

Adding this in the beginning of filter chains should make filtering
faster due to better use of the memory cache.

@section split

Split input video into several identical outputs.

The filter accepts a single parameter which specifies the number of outputs. If
unspecified, it defaults to 2.

For example
@example
ffmpeg -i INPUT -filter_complex split=5 OUTPUT
@end example
will create 5 copies of the input video.

For example:
@example
[in] split [splitout1][splitout2];
[splitout1] crop=100:100:0:0    [cropout];
[splitout2] pad=200:200:100:100 [padout];
@end example

will create two separate outputs from the same input, one cropped and
one padded.

@section super2xsai

Scale the input by 2x and smooth using the Super2xSaI (Scale and
Interpolate) pixel art scaling algorithm.

Useful for enlarging pixel art images without reducing sharpness.

@section swapuv
Swap U & V plane.

@section thumbnail
Select the most representative frame in a given sequence of consecutive frames.

It accepts as argument the frames batch size to analyze (default @var{N}=100);
in a set of @var{N} frames, the filter will pick one of them, and then handle
the next batch of @var{N} frames until the end.

Since the filter keeps track of the whole frames sequence, a bigger @var{N}
value will result in a higher memory usage, so a high value is not recommended.

The following example extract one picture each 50 frames:
@example
thumbnail=50
@end example

Complete example of a thumbnail creation with @command{ffmpeg}:
@example
ffmpeg -i in.avi -vf thumbnail,scale=300:200 -frames:v 1 out.png
@end example

@section tile

Tile several successive frames together.

It accepts as argument the tile size (i.e. the number of lines and columns)
in the form "@var{w}x@var{h}".

For example, produce 8×8 PNG tiles of all keyframes (@option{-skip_frame
nokey}) in a movie:
@example
ffmpeg -skip_frame nokey -i file.avi -vf 'scale=128:72,tile=8x8' -an -vsync 0 keyframes%03d.png
@end example
The @option{-vsync 0} is necessary to prevent @command{ffmpeg} from
duplicating each output frame to accomodate the originally detected frame
rate.

@section tinterlace

Perform various types of temporal field interlacing.

Frames are counted starting from 1, so the first input frame is
considered odd.

This filter accepts a single parameter specifying the mode. Available
modes are:

@table @samp
@item merge, 0
Move odd frames into the upper field, even into the lower field,
generating a double height frame at half framerate.

@item drop_odd, 1
Only output even frames, odd frames are dropped, generating a frame with
unchanged height at half framerate.

@item drop_even, 2
Only output odd frames, even frames are dropped, generating a frame with
unchanged height at half framerate.

@item pad, 3
Expand each frame to full height, but pad alternate lines with black,
generating a frame with double height at the same input framerate.

@item interleave_top, 4
Interleave the upper field from odd frames with the lower field from
even frames, generating a frame with unchanged height at half framerate.

@item interleave_bottom, 5
Interleave the lower field from odd frames with the upper field from
even frames, generating a frame with unchanged height at half framerate.

@item interlacex2, 6
Double frame rate with unchanged height. Frames are inserted each
containing the second temporal field from the previous input frame and
the first temporal field from the next input frame. This mode relies on
the top_field_first flag. Useful for interlaced video displays with no
field synchronisation.
@end table

Numeric values are deprecated but are accepted for backward
compatibility reasons.

Default mode is @code{merge}.

@section transpose

Transpose rows with columns in the input video and optionally flip it.

It accepts a parameter representing an integer, which can assume the
values:

@table @samp
@item 0
Rotate by 90 degrees counterclockwise and vertically flip (default), that is:
@example
L.R     L.l
. . ->  . .
l.r     R.r
@end example

@item 1
Rotate by 90 degrees clockwise, that is:
@example
L.R     l.L
. . ->  . .
l.r     r.R
@end example

@item 2
Rotate by 90 degrees counterclockwise, that is:
@example
L.R     R.r
. . ->  . .
l.r     L.l
@end example

@item 3
Rotate by 90 degrees clockwise and vertically flip, that is:
@example
L.R     r.R
. . ->  . .
l.r     l.L
@end example
@end table

@section unsharp

Sharpen or blur the input video.

It accepts the following parameters:
@var{luma_msize_x}:@var{luma_msize_y}:@var{luma_amount}:@var{chroma_msize_x}:@var{chroma_msize_y}:@var{chroma_amount}

Negative values for the amount will blur the input video, while positive
values will sharpen. All parameters are optional and default to the
equivalent of the string '5:5:1.0:5:5:0.0'.

@table @option

@item luma_msize_x
Set the luma matrix horizontal size. It can be an integer between 3
and 13, default value is 5.

@item luma_msize_y
Set the luma matrix vertical size. It can be an integer between 3
and 13, default value is 5.

@item luma_amount
Set the luma effect strength. It can be a float number between -2.0
and 5.0, default value is 1.0.

@item chroma_msize_x
Set the chroma matrix horizontal size. It can be an integer between 3
and 13, default value is 5.

@item chroma_msize_y
Set the chroma matrix vertical size. It can be an integer between 3
and 13, default value is 5.

@item chroma_amount
Set the chroma effect strength. It can be a float number between -2.0
and 5.0, default value is 0.0.

@end table

@example
# Strong luma sharpen effect parameters
unsharp=7:7:2.5

# Strong blur of both luma and chroma parameters
unsharp=7:7:-2:7:7:-2

# Use the default values with @command{ffmpeg}
ffmpeg -i in.avi -vf "unsharp" out.mp4
@end example

@section vflip

Flip the input video vertically.

@example
ffmpeg -i in.avi -vf "vflip" out.avi
@end example

@section yadif

Deinterlace the input video ("yadif" means "yet another deinterlacing
filter").

It accepts the optional parameters: @var{mode}:@var{parity}:@var{auto}.

@var{mode} specifies the interlacing mode to adopt, accepts one of the
following values:

@table @option
@item 0
output 1 frame for each frame
@item 1
output 1 frame for each field
@item 2
like 0 but skips spatial interlacing check
@item 3
like 1 but skips spatial interlacing check
@end table

Default value is 0.

@var{parity} specifies the picture field parity assumed for the input
interlaced video, accepts one of the following values:

@table @option
@item 0
assume top field first
@item 1
assume bottom field first
@item -1
enable automatic detection
@end table

Default value is -1.
If interlacing is unknown or decoder does not export this information,
top field first will be assumed.

@var{auto} specifies if deinterlacer should trust the interlaced flag
and only deinterlace frames marked as interlaced

@table @option
@item 0
deinterlace all frames
@item 1
only deinterlace frames marked as interlaced
@end table

Default value is 0.

@c man end VIDEO FILTERS

@chapter Video Sources
@c man begin VIDEO SOURCES

Below is a description of the currently available video sources.

@section buffer

Buffer video frames, and make them available to the filter chain.

This source is mainly intended for a programmatic use, in particular
through the interface defined in @file{libavfilter/vsrc_buffer.h}.

It accepts a list of options in the form of @var{key}=@var{value} pairs
separated by ":". A descroption of the accepted options follows.

@table @option

@item video_size
Specify the size (width and height) of the buffered video frames.

@item pix_fmt
A string representing the pixel format of the buffered video frames.
It may be a number corresponding to a pixel format, or a pixel format
name.

@item time_base
Specify the timebase assumed by the timestamps of the buffered frames.

@item time_base
Specify the frame rate expected for the video stream.

@item pixel_aspect
Specify the sample aspect ratio assumed by the video frames.

@item sws_param
Specify the optional parameters to be used for the scale filter which
is automatically inserted when an input change is detected in the
input size or format.
@end table

For example:
@example
buffer=size=320x240:pix_fmt=yuv410p:time_base=1/24:pixel_aspect=1/1
@end example

will instruct the source to accept video frames with size 320x240 and
with format "yuv410p", assuming 1/24 as the timestamps timebase and
square pixels (1:1 sample aspect ratio).
Since the pixel format with name "yuv410p" corresponds to the number 6
(check the enum PixelFormat definition in @file{libavutil/pixfmt.h}),
this example corresponds to:
@example
buffer=size=320x240:pixfmt=6:time_base=1/24:pixel_aspect=1/1
@end example

Alternatively, the options can be specified as a flat string, but this
syntax is deprecated:

@var{width}:@var{height}:@var{pix_fmt}:@var{time_base.num}:@var{time_base.den}:@var{pixel_aspect.num}:@var{pixel_aspect.den}[:@var{sws_param}]

@section cellauto

Create a pattern generated by an elementary cellular automaton.

The initial state of the cellular automaton can be defined through the
@option{filename}, and @option{pattern} options. If such options are
not specified an initial state is created randomly.

At each new frame a new row in the video is filled with the result of
the cellular automaton next generation. The behavior when the whole
frame is filled is defined by the @option{scroll} option.

This source accepts a list of options in the form of
@var{key}=@var{value} pairs separated by ":". A description of the
accepted options follows.

@table @option
@item filename, f
Read the initial cellular automaton state, i.e. the starting row, from
the specified file.
In the file, each non-whitespace character is considered an alive
cell, a newline will terminate the row, and further characters in the
file will be ignored.

@item pattern, p
Read the initial cellular automaton state, i.e. the starting row, from
the specified string.

Each non-whitespace character in the string is considered an alive
cell, a newline will terminate the row, and further characters in the
string will be ignored.

@item rate, r
Set the video rate, that is the number of frames generated per second.
Default is 25.

@item random_fill_ratio, ratio
Set the random fill ratio for the initial cellular automaton row. It
is a floating point number value ranging from 0 to 1, defaults to
1/PHI.

This option is ignored when a file or a pattern is specified.

@item random_seed, seed
Set the seed for filling randomly the initial row, must be an integer
included between 0 and UINT32_MAX. If not specified, or if explicitly
set to -1, the filter will try to use a good random seed on a best
effort basis.

@item rule
Set the cellular automaton rule, it is a number ranging from 0 to 255.
Default value is 110.

@item size, s
Set the size of the output video.

If @option{filename} or @option{pattern} is specified, the size is set
by default to the width of the specified initial state row, and the
height is set to @var{width} * PHI.

If @option{size} is set, it must contain the width of the specified
pattern string, and the specified pattern will be centered in the
larger row.

If a filename or a pattern string is not specified, the size value
defaults to "320x518" (used for a randomly generated initial state).

@item scroll
If set to 1, scroll the output upward when all the rows in the output
have been already filled. If set to 0, the new generated row will be
written over the top row just after the bottom row is filled.
Defaults to 1.

@item start_full, full
If set to 1, completely fill the output with generated rows before
outputting the first frame.
This is the default behavior, for disabling set the value to 0.

@item stitch
If set to 1, stitch the left and right row edges together.
This is the default behavior, for disabling set the value to 0.
@end table

@subsection Examples

@itemize
@item
Read the initial state from @file{pattern}, and specify an output of
size 200x400.
@example
cellauto=f=pattern:s=200x400
@end example

@item
Generate a random initial row with a width of 200 cells, with a fill
ratio of 2/3:
@example
cellauto=ratio=2/3:s=200x200
@end example

@item
Create a pattern generated by rule 18 starting by a single alive cell
centered on an initial row with width 100:
@example
cellauto=p=@@:s=100x400:full=0:rule=18
@end example

@item
Specify a more elaborated initial pattern:
@example
cellauto=p='@@@@ @@ @@@@':s=100x400:full=0:rule=18
@end example

@end itemize

@section color

Provide an uniformly colored input.

This source accepts list of options in the form of
@var{key}=@var{value} pairs separated by ":".

Alternatively, it accepts a string in the form
@var{color}:@var{size}:@var{rate}, but this syntax is
deprecated.

Follows the description of the accepted parameters.

@table @option

@item color, c
Specify the color of the source. It can be the name of a color (case
insensitive match) or a 0xRRGGBB[AA] sequence, possibly followed by an
alpha specifier. The default value is "black".

@item size, s
Specify the size of the sourced video, it may be a string of the form
@var{width}x@var{height}, or the name of a size abbreviation. The
default value is "320x240".

@item rate, r
Specify the frame rate of the sourced video, as the number of frames
generated per second. It has to be a string in the format
@var{frame_rate_num}/@var{frame_rate_den}, an integer number, a float
number or a valid video frame rate abbreviation. The default value is
"25".

@end table

For example the following graph description will generate a red source
with an opacity of 0.2, with size "qcif" and a frame rate of 10
frames per second, which will be overlayed over the source connected
to the pad with identifier "in".

@example
"color=c=red@@0.2:s=qcif:r=10 [color]; [in][color] overlay [out]"
@end example

@anchor{src_movie}
@section movie

Read audio and/or video stream(s) from a movie container.

It accepts the syntax: @var{movie_name}[:@var{options}] where
@var{movie_name} is the name of the resource to read (not necessarily
a file but also a device or a stream accessed through some protocol),
and @var{options} is an optional sequence of @var{key}=@var{value}
pairs, separated by ":".

The description of the accepted options follows.

@table @option

@item format_name, f
Specifies the format assumed for the movie to read, and can be either
the name of a container or an input device. If not specified the
format is guessed from @var{movie_name} or by probing.

@item seek_point, sp
Specifies the seek point in seconds, the frames will be output
starting from this seek point, the parameter is evaluated with
@code{av_strtod} so the numerical value may be suffixed by an IS
postfix. Default value is "0".

@item streams, s
Specifies the streams to read. Several streams can be specified, separated
by "+". The source will then have as many outputs, in the same order. The
syntax is explained in the @ref{Stream specifiers} chapter. Two special
names, "dv" and "da" specify respectively the default (best suited) video
and audio stream. Default is "dv", or "da" if the filter is called as
"amovie".

@item stream_index, si
Specifies the index of the video stream to read. If the value is -1,
the best suited video stream will be automatically selected. Default
value is "-1". Deprecated. If the filter is called "amovie", it will select
audio instead of video.

@item loop
Specifies how many times to read the stream in sequence.
If the value is less than 1, the stream will be read again and again.
Default value is "1".

Note that when the movie is looped the source timestamps are not
changed, so it will generate non monotonically increasing timestamps.
@end table

This filter allows to overlay a second video on top of main input of
a filtergraph as shown in this graph:
@example
input -----------> deltapts0 --> overlay --> output
                                    ^
                                    |
movie --> scale--> deltapts1 -------+
@end example

Some examples follow:
@example
# skip 3.2 seconds from the start of the avi file in.avi, and overlay it
# on top of the input labelled as "in".
movie=in.avi:seek_point=3.2, scale=180:-1, setpts=PTS-STARTPTS [movie];
[in] setpts=PTS-STARTPTS, [movie] overlay=16:16 [out]

# read from a video4linux2 device, and overlay it on top of the input
# labelled as "in"
movie=/dev/video0:f=video4linux2, scale=180:-1, setpts=PTS-STARTPTS [movie];
[in] setpts=PTS-STARTPTS, [movie] overlay=16:16 [out]

# read the first video stream and the audio stream with id 0x81 from
# dvd.vob; the video is connected to the pad named "video" and the audio is
# connected to the pad named "audio":
movie=dvd.vob:s=v:0+#0x81 [video] [audio]
@end example

@section mptestsrc

Generate various test patterns, as generated by the MPlayer test filter.

The size of the generated video is fixed, and is 256x256.
This source is useful in particular for testing encoding features.

This source accepts an optional sequence of @var{key}=@var{value} pairs,
separated by ":". The description of the accepted options follows.

@table @option

@item rate, r
Specify the frame rate of the sourced video, as the number of frames
generated per second. It has to be a string in the format
@var{frame_rate_num}/@var{frame_rate_den}, an integer number, a float
number or a valid video frame rate abbreviation. The default value is
"25".

@item duration, d
Set the video duration of the sourced video. The accepted syntax is:
@example
[-]HH:MM:SS[.m...]
[-]S+[.m...]
@end example
See also the function @code{av_parse_time()}.

If not specified, or the expressed duration is negative, the video is
supposed to be generated forever.

@item test, t

Set the number or the name of the test to perform. Supported tests are:
@table @option
@item dc_luma
@item dc_chroma
@item freq_luma
@item freq_chroma
@item amp_luma
@item amp_chroma
@item cbp
@item mv
@item ring1
@item ring2
@item all
@end table

Default value is "all", which will cycle through the list of all tests.
@end table

For example the following:
@example
testsrc=t=dc_luma
@end example

will generate a "dc_luma" test pattern.

@section frei0r_src

Provide a frei0r source.

To enable compilation of this filter you need to install the frei0r
header and configure FFmpeg with @code{--enable-frei0r}.

The source supports the syntax:
@example
@var{size}:@var{rate}:@var{src_name}[@{=|:@}@var{param1}:@var{param2}:...:@var{paramN}]
@end example

@var{size} is the size of the video to generate, may be a string of the
form @var{width}x@var{height} or a frame size abbreviation.
@var{rate} is the rate of the video to generate, may be a string of
the form @var{num}/@var{den} or a frame rate abbreviation.
@var{src_name} is the name to the frei0r source to load. For more
information regarding frei0r and how to set the parameters read the
section @ref{frei0r} in the description of the video filters.

For example, to generate a frei0r partik0l source with size 200x200
and frame rate 10 which is overlayed on the overlay filter main input:
@example
frei0r_src=200x200:10:partik0l=1234 [overlay]; [in][overlay] overlay
@end example

@section life

Generate a life pattern.

This source is based on a generalization of John Conway's life game.

The sourced input represents a life grid, each pixel represents a cell
which can be in one of two possible states, alive or dead. Every cell
interacts with its eight neighbours, which are the cells that are
horizontally, vertically, or diagonally adjacent.

At each interaction the grid evolves according to the adopted rule,
which specifies the number of neighbor alive cells which will make a
cell stay alive or born. The @option{rule} option allows to specify
the rule to adopt.

This source accepts a list of options in the form of
@var{key}=@var{value} pairs separated by ":". A description of the
accepted options follows.

@table @option
@item filename, f
Set the file from which to read the initial grid state. In the file,
each non-whitespace character is considered an alive cell, and newline
is used to delimit the end of each row.

If this option is not specified, the initial grid is generated
randomly.

@item rate, r
Set the video rate, that is the number of frames generated per second.
Default is 25.

@item random_fill_ratio, ratio
Set the random fill ratio for the initial random grid. It is a
floating point number value ranging from 0 to 1, defaults to 1/PHI.
It is ignored when a file is specified.

@item random_seed, seed
Set the seed for filling the initial random grid, must be an integer
included between 0 and UINT32_MAX. If not specified, or if explicitly
set to -1, the filter will try to use a good random seed on a best
effort basis.

@item rule
Set the life rule.

A rule can be specified with a code of the kind "S@var{NS}/B@var{NB}",
where @var{NS} and @var{NB} are sequences of numbers in the range 0-8,
@var{NS} specifies the number of alive neighbor cells which make a
live cell stay alive, and @var{NB} the number of alive neighbor cells
which make a dead cell to become alive (i.e. to "born").
"s" and "b" can be used in place of "S" and "B", respectively.

Alternatively a rule can be specified by an 18-bits integer. The 9
high order bits are used to encode the next cell state if it is alive
for each number of neighbor alive cells, the low order bits specify
the rule for "borning" new cells. Higher order bits encode for an
higher number of neighbor cells.
For example the number 6153 = @code{(12<<9)+9} specifies a stay alive
rule of 12 and a born rule of 9, which corresponds to "S23/B03".

Default value is "S23/B3", which is the original Conway's game of life
rule, and will keep a cell alive if it has 2 or 3 neighbor alive
cells, and will born a new cell if there are three alive cells around
a dead cell.

@item size, s
Set the size of the output video.

If @option{filename} is specified, the size is set by default to the
same size of the input file. If @option{size} is set, it must contain
the size specified in the input file, and the initial grid defined in
that file is centered in the larger resulting area.

If a filename is not specified, the size value defaults to "320x240"
(used for a randomly generated initial grid).

@item stitch
If set to 1, stitch the left and right grid edges together, and the
top and bottom edges also. Defaults to 1.

@item mold
Set cell mold speed. If set, a dead cell will go from @option{death_color} to
@option{mold_color} with a step of @option{mold}. @option{mold} can have a
value from 0 to 255.

@item life_color
Set the color of living (or new born) cells.

@item death_color
Set the color of dead cells. If @option{mold} is set, this is the first color
used to represent a dead cell.

@item mold_color
Set mold color, for definitely dead and moldy cells.
@end table

@subsection Examples

@itemize
@item
Read a grid from @file{pattern}, and center it on a grid of size
300x300 pixels:
@example
life=f=pattern:s=300x300
@end example

@item
Generate a random grid of size 200x200, with a fill ratio of 2/3:
@example
life=ratio=2/3:s=200x200
@end example

@item
Specify a custom rule for evolving a randomly generated grid:
@example
life=rule=S14/B34
@end example

@item
Full example with slow death effect (mold) using @command{ffplay}:
@example
ffplay -f lavfi life=s=300x200:mold=10:r=60:ratio=0.1:death_color=#C83232:life_color=#00ff00,scale=1200:800:flags=16
@end example
@end itemize

@section nullsrc, rgbtestsrc, testsrc

The @code{nullsrc} source returns unprocessed video frames. It is
mainly useful to be employed in analysis / debugging tools, or as the
source for filters which ignore the input data.

The @code{rgbtestsrc} source generates an RGB test pattern useful for
detecting RGB vs BGR issues. You should see a red, green and blue
stripe from top to bottom.

The @code{testsrc} source generates a test video pattern, showing a
color pattern, a scrolling gradient and a timestamp. This is mainly
intended for testing purposes.

These sources accept an optional sequence of @var{key}=@var{value} pairs,
separated by ":". The description of the accepted options follows.

@table @option

@item size, s
Specify the size of the sourced video, it may be a string of the form
@var{width}x@var{height}, or the name of a size abbreviation. The
default value is "320x240".

@item rate, r
Specify the frame rate of the sourced video, as the number of frames
generated per second. It has to be a string in the format
@var{frame_rate_num}/@var{frame_rate_den}, an integer number, a float
number or a valid video frame rate abbreviation. The default value is
"25".

@item sar
Set the sample aspect ratio of the sourced video.

@item duration, d
Set the video duration of the sourced video. The accepted syntax is:
@example
[-]HH[:MM[:SS[.m...]]]
[-]S+[.m...]
@end example
See also the function @code{av_parse_time()}.

If not specified, or the expressed duration is negative, the video is
supposed to be generated forever.

@item decimals, n
Set the number of decimals to show in the timestamp, only used in the
@code{testsrc} source.

The displayed timestamp value will correspond to the original
timestamp value multiplied by the power of 10 of the specified
value. Default value is 0.
@end table

For example the following:
@example
testsrc=duration=5.3:size=qcif:rate=10
@end example

will generate a video with a duration of 5.3 seconds, with size
176x144 and a frame rate of 10 frames per second.

If the input content is to be ignored, @code{nullsrc} can be used. The
following command generates noise in the luminance plane by employing
the @code{mp=geq} filter:
@example
nullsrc=s=256x256, mp=geq=random(1)*255:128:128
@end example

@c man end VIDEO SOURCES

@chapter Video Sinks
@c man begin VIDEO SINKS

Below is a description of the currently available video sinks.

@section buffersink

Buffer video frames, and make them available to the end of the filter
graph.

This sink is mainly intended for a programmatic use, in particular
through the interface defined in @file{libavfilter/buffersink.h}.

It does not require a string parameter in input, but you need to
specify a pointer to a list of supported pixel formats terminated by
-1 in the opaque parameter provided to @code{avfilter_init_filter}
when initializing this sink.

@section nullsink

Null video sink, do absolutely nothing with the input video. It is
mainly useful as a template and to be employed in analysis / debugging
tools.

@c man end VIDEO SINKS

@chapter Multimedia Filters
@c man begin MULTIMEDIA FILTERS

Below is a description of the currently available multimedia filters.

@section concat

Concatenate audio and video streams, joining them together one after the
other.

The filter works on segments of synchronized video and audio streams. All
segments must have the same number of streams of each type, and that will
also be the number of streams at output.

The filter accepts the following named parameters:
@table @option

@item n
Set the number of segments. Default is 2.

@item v
Set the number of output video streams, that is also the number of video
streams in each segment. Default is 1.

@item a
Set the number of output audio streams, that is also the number of video
streams in each segment. Default is 0.

@end table

The filter has @var{v}+@var{a} outputs: first @var{v} video outputs, then
@var{a} audio outputs.

There are @var{n}×(@var{v}+@var{a}) inputs: first the inputs for the first
segment, in the same order as the outputs, then the inputs for the second
segment, etc.

Related streams do not always have exactly the same duration, for various
reasons including codec frame size or sloppy authoring. For that reason,
related synchronized streams (e.g. a video and its audio track) should be
concatenated at once. The concat filter will use the duration of the longest
stream in each segment (except the last one), and if necessary pad shorter
audio streams with silence.

For this filter to work correctly, all segments must start at timestamp 0.

All corresponding streams must have the same parameters in all segments; the
filtering system will automatically select a common pixel format for video
streams, and a common sample format, sample rate and channel layout for
audio streams, but other settings, such as resolution, must be converted
explicitly by the user.

Different frame rates are acceptable but will result in variable frame rate
at output; be sure to configure the output file to handle it.

Examples:
@itemize
@item
Concatenate an opening, an episode and an ending, all in bilingual version
(video in stream 0, audio in streams 1 and 2):
@example
ffmpeg -i opening.mkv -i episode.mkv -i ending.mkv -filter_complex \
  '[0:0] [0:1] [0:2] [1:0] [1:1] [1:2] [2:0] [2:1] [2:2]
   concat=n=3:v=1:a=2 [v] [a1] [a2]' \
  -map '[v]' -map '[a1]' -map '[a2]' output.mkv
@end example

@item
Concatenate two parts, handling audio and video separately, using the
(a)movie sources, and adjusting the resolution:
@example
movie=part1.mp4, scale=512:288 [v1] ; amovie=part1.mp4 [a1] ;
movie=part2.mp4, scale=512:288 [v2] ; amovie=part2.mp4 [a2] ;
[v1] [v2] concat [outv] ; [a1] [a2] concat=v=0:a=1 [outa]
@end example
Note that a desync will happen at the stitch if the audio and video streams
do not have exactly the same duration in the first file.

@end itemize

@section showwaves

Convert input audio to a video output, representing the samples waves.

The filter accepts the following named parameters:
@table @option

@item n
Set the number of samples which are printed on the same column. A
larger value will decrease the frame rate. Must be a positive
integer. This option can be set only if the value for @var{rate}
is not explicitly specified.

@item rate, r
Set the (approximate) output frame rate. This is done by setting the
option @var{n}. Default value is "25".

@item size, s
Specify the video size for the output. Default value is "600x240".
@end table

Some examples follow.
@itemize
@item
Output the input file audio and the corresponding video representation
at the same time:
@example
amovie=a.mp3,asplit[out0],showwaves[out1]
@end example

@item
Create a synthetic signal and show it with showwaves, forcing a
framerate of 30 frames per second:
@example
aevalsrc=sin(1*2*PI*t)*sin(880*2*PI*t):cos(2*PI*200*t),asplit[out0],showwaves=r=30[out1]
@end example
@end itemize

@c man end MULTIMEDIA FILTERS
