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Linshizhi
ffmpeg.wasm-core
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2acc525d
Commit
2acc525d
authored
Oct 30, 2013
by
Stefano Sabatini
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doc/encoders: add libfaac encoder documentation
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doc/encoders.texi
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2acc525d
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@@ -38,8 +38,8 @@ As this encoder is experimental, unexpected behavior may exist from time to
time. For a more stable AAC encoder, see @ref{libvo-aacenc}. However, be warned
that it has a worse quality reported by some users.
@c todo @ref{lib
faac}, @ref{lib
aacplus}
See also @ref{libfdk-aac-enc,,
the libfdk_aac section
}.
@c todo @ref{libaacplus}
See also @ref{libfdk-aac-enc,,
libfdk_aac} and @ref{libfaac
}.
@subsection Options
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@@ -494,6 +494,113 @@ Selected by Encoder (default)
@end table
@anchor{libfaac}
@section libfaac
libfaac AAC (Advanced Audio Coding) encoder wrapper.
Requires the presence of the libfaac headers and library during
configuration. You need to explicitly configure the build with
@code{--enable-libfaac --enable-nonfree}.
This encoder is considered to be of higher quality with respect to the
@ref{aacenc,,the native experimental FFmpeg AAC encoder}.
For more information see the libfaac project at
@url{http://www.audiocoding.com/faac.html/}.
@subsection Options
The following shared FFmpeg codec options are recognized.
The following options are supported by the libfaac wrapper. The
@command{faac}-equivalent of the options are listed in parentheses.
@table @option
@item b (@emph{-b})
Set bit rate in bits/s for ABR (Average Bit Rate) mode. If the bit rate
is not explicitly specified, it is automatically set to a suitable
value depending on the selected profile. @command{faac} bitrate is
expressed in kilobits/s.
Note that libfaac does not support CBR (Constant Bit Rate) but only
ABR (Average Bit Rate).
If VBR mode is enabled this option is ignored.
@item ar (@emph{-R})
Set audio sampling rate (in Hz).
@item ac (@emph{-c})
Set the number of audio channels.
@item cutoff (@emph{-C})
Set cutoff frequency. If not specified (or explicitly set to 0) it
will use a value automatically computed by the library. Default value
is 0.
@item profile
Set audio profile.
The following profiles are recognized:
@table @samp
@item aac_main
Main AAC (Main)
@item aac_low
Low Complexity AAC (LC)
@item aac_ssr
Scalable Sample Rate (SSR)
@item aac_ltp
Long Term Prediction (LTP)
@end table
If not specified it is set to @samp{aac_low}.
@item flags +qscale
Set constant quality VBR (Variable Bit Rate) mode.
@item global_quality
Set quality in VBR mode as an integer number of lambda units.
Only relevant when VBR mode is enabled with @code{flags +qscale}. The
value is converted to QP units by dividing it by @code{FF_QP2LAMBDA},
and used to set the quality value used by libfaac. A reasonable range
for the option value in QP units is [10-500], the higher the value the
higher the quality.
@item q (@emph{-q})
Enable VBR mode when set to a non-negative value, and set constant
quality value as a double floating point value in QP units.
The value sets the quality value used by libfaac. A reasonable range
for the option value is [10-500], the higher the value the higher the
quality.
This option is valid only using the @command{ffmpeg} command-line
tool. For library interface users, use @option{global_quality}.
@end table
@subsection Examples
@itemize
@item
Use @command{ffmpeg} to convert an audio file to ABR 128 kbps AAC in an M4A (MP4)
container:
@example
ffmpeg -i input.wav -codec:a libfaac -b:a 128k -output.m4a
@end example
@item
Use @command{ffmpeg} to convert an audio file to VBR AAC, using the
LTP AAC profile:
@example
ffmpeg -i input.wav -c:a libfaac -profile:a aac_ltp -q:a 100 output.m4a
@end example
@end itemize
@anchor{libfdk-aac-enc}
@section libfdk_aac
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