Up until now, one last kind of unknown-length element hasn't been
properly handled: Unknown-length elements that are supposed to be
skipped, i.e. the level 1 elements that might reside after the
clusters.

This commit changes this. To do this, ebml_parse got a mode that
essentially tries to skip everything except when parsing is needed
(namely for unknown-length elements for which parsing is necessary
as they can't be skipped). This mode is selected by using a NULL
as destination where the parsed data should be written to.
It is used to parse the level 1 elements in matroska_parse_cluster.

The syntax list used for parsing must of course include links to
the syntax of all the master elements that might need to be parsed.
In other words: Instead of matroska_clusters (which contained every
level 1 element except clusters as EBML_NONE elements designated to
be skipped) matroska_segment is needed and used; matroska_clusters has
been removed.

Furthermore, matroska_segment has been reordered so that clusters are at
the front as this is now the most common case for this list.
Signed-off-by: Andreas Rheinhardt <andreas.rheinhardt@gmail.com>

matroska_probe did not support the case of an unknown-length EBML header
at all; given that libavformat's Matroska muxer used to produce such
files in the streaming case, support for them has been added.
Signed-off-by: Andreas Rheinhardt <andreas.rheinhardt@gmail.com>

The current Matroska specifications mandate that only two elements may
use an unknown-length length: Segments and clusters. But this was not
always so: For the greater part of Matroska's existence, all master
elements were allowed to make use of the unknown-length feature.

And there were muxers creating such files: For several years
libavformat's Matroska muxer used unknown-length for all master
elements when the output wasn't seekable. This only stopped in March
2010 with 2529bb30. And even afterwards it was possible (albeit
unlikely) for libavformat to create unknown-length master elements
that are in violation of today's specifications, namely if the master
element was so big that the seek backwards to update the size could
no longer be performed inside the AVIOContext's write buffer. This
has only been fixed in October 2016 (with the patches that introduced
support for writing CRC-32 elements).

Libavformat's Matroska demuxer meanwhile has never really supported
unknown-length elements besides segments and clusters. Support for the
latter was hardcoded. This commit changes this: Now all master elements
for which a syntax to parse them is available are supported. This
includes the files produced by old versions of libavformat's muxer.

More precisely, master elements that have unknown length and are about
to be parsed (not skipped) are supported; only a warning is emitted for
them. For normal files, this means that level 1 elements after the
clusters that are encountered after the clusters have been parsed (i.e.
not because they are referenced by the seekhead at the beginning of the
file) are still unsupported (they would be skipped at this point if
their length were known).
Signed-off-by: Andreas Rheinhardt <andreas.rheinhardt@gmail.com>

1. Up until now, the error message for EBML numbers whose length exceeds
the limits imposed upon them because of the element's type did not
distinguish between known-length and unknown-length elements. As a
consequence, the numerical value of the define constant
EBML_UNKNOWN_LENGTH was emitted as part of the error message which is
of course not appropriate. This commit changes this by adding error
messages designed for unknown-length elements.

2. We impose some (arbitrary) sanity checks on the lengths of certain
element types; these checks were conducted before the checks depending
on whether the element exceeds its containing master element. Now the
order has been reversed, because a failure at the (formerly) latter
check implies that the file is truly erroneous and not only fails our
arbitrary length limit. Moreover, this increases the informativeness of
the error messages.

3. Furthermore, the error message in general has been changed by replacing
the type of the element (something internal to this demuxer and
therefore suitable as debug output at best, not as an error message
intended for ordinary users) with the element ID. The element's position
has been added, too.

4. Finally, the length limit for EBML_NONE elements has been changed so
that all unknown-length elements of EBML_NONE-type trigger an error.
This is done because unknown-length elements can't be skipped and need
to be parsed, but there is no syntax to parse available for EBML_NONE
elements. This is done in preparation for a further patch which allows
more unknown-length elements than just clusters and segments.
Signed-off-by: Andreas Rheinhardt <andreas.rheinhardt@gmail.com>

The Matroska (and WebM) file format achieves forward-compability by
insisting that demuxers ignore and skip elements they don't know about.
Unfortunately, this complicates the detection of errors as errors
resulting from loosing sync can't be reliably distinguished from
unknown elements that are part of a future version of the standard.

Up until now, the strategy to deal with this situation was to skip all
unknown elements that are not obviously erroneous; if an error happened,
it was tried to seek to the last known good position to resync from (and
resync to level 1 elements). This is working fine if the input is
seekable, but if it is not, then the skipped data can usually not be
rechecked lateron. This is particularly acute if unknown-length clusters
are in use, as the check for whether a child element exceeds the
containing master element is ineffective in this situation.

To remedy this, a new heuristic has been introduced: If an unknown
element is encountered in non-seekable mode, an error is presumed to
have happened based upon a combination of the length of the row of the
already encountered unknown elements and of how far away skipping this
element would take us.
Signed-off-by: Andreas Rheinhardt <andreas.rheinhardt@gmail.com>

Cosmetics include reordering EbmlType so that EBML_SINT is adjacent to
the other numbers (and matches the order in the switch in ebml_parse)
and also reordering the switch for assignment of default values so that
it matches the order in EbmlType.
Signed-off-by: Andreas Rheinhardt <andreas.rheinhardt@gmail.com>

Up until now, avio_tell was used multiple times in ebml_parse and its
subroutines, although the result of these calls can usually be simply
derived from the result of earlier calls to avio_tell. This has been
changed. Unnecessary calls to avio_tell in ebml_parse are avoided now.

Furthermore, there has been a slight change in the output of some error
messages relating to elements exceeding their containing master element:
The reported position of the element now points to the first byte of the
element ID and no longer to the first byte of the element's payload.
Signed-off-by: Andreas Rheinhardt <andreas.rheinhardt@gmail.com>

This commit closes the last hole in the system of checks for a
known-length file ending too early: Now an error message is emitted
in case the file ends directly after an EBML element.

Furthermore, this commit adds a check and a corresponding warning
whether there is data beyond the Matroska segment (only reasonable for
known-length segments). If everything looks alright, then parsing is
stopped as soon as EOF is reached (in contrast, the earlier code would
always call matroska_resync at the end).
Signed-off-by: Andreas Rheinhardt <andreas.rheinhardt@gmail.com>

By including SimpleBlocks and BlockGroups twice in the same EbmlSyntax
array (with different semantics), one can reduce the duplication of the
other values.
Signed-off-by: Andreas Rheinhardt <andreas.rheinhardt@gmail.com>

The new code does not rely on whether the cluster's position is set or
not to infer whether a cluster needs to be closed or not (instead, this
is done in ebml_parse), so there is no need to reset the cluster's
position at all any more. It will be automatically set to the correct
value when a cluster is entered.
Signed-off-by: Andreas Rheinhardt <andreas.rheinhardt@gmail.com>

Before this commit, the parsing of clusters mixed EBML levels by
allowing elements from different levels in a EbmlSyntax (namely
matroska_cluster_parsing). This has been changed. And the level
is now explicitly used to determine how to parse.
Signed-off-by: Andreas Rheinhardt <andreas.rheinhardt@gmail.com>

This commit changes how levels are handled: If the level used for
ebml_parse ends directly after an element that has been consumed, then
ebml_parse ends the level itself (and any known-length levels that end
there as well) and informs the caller via the return value; if the
current level is of unknown-length, then the level is ended as soon as
an element that is not valid on the current level, but on a higher
level is encountered (or if EOF has been encountered).

This is designed for situations where one wants to parse master elements
incrementally, i.e. not in one go via ebml_parse_nest.

The (incremental) parsing of clusters still mixes levels by using a
syntax list that contains elements from different levels and the level
is still ended manually via a call to ebml_level_end if the last cluster
was an unknown-length cluster (known-length clusters are already ended
when their last element is read), but only if the next element is a
cluster, too. A  different level 1 element following an unknown-length
cluster will currently simply be presumed to be part of the earlier
cluster. Fixing this will be done in a future patch. The modifications
to matroska_parse_cluster contained in this patch are only intended not
to cause regressions.

Nevertheless, the fact that known-length levels are automatically ended
in ebml_parse when their last element has been read already fixes a bogus
error message introduced in 9326117b that was emitted when a known-length
cluster is followed by another level 1 element other than a cluster in
which case the cluster's level was not ended (which only happened when
a new cluster has been encountered) so that the length check (introduced
in 9326117b) failed for the level 1 element as it is of course not
contained in the previous cluster. Most Matroska files were affected by
this.
Signed-off-by: Andreas Rheinhardt <andreas.rheinhardt@gmail.com>

By linking to the syntax of the parent (i.e. the containing master
element) one can check whether an element is actually part of a higher
level in the EBML hierarchy. Knowing this is important for
unknown-length levels, because they end when an element that doesn't
belong to this, but to a higher hierarchy level is encountered.

Sometimes there are different syntaxes dealing with the same elements.
In this case it is important to use a parent that contains all the
elements at the parent level; whether this is the syntax actually used
to enter the child's level is irrelevant. This affects the list of level
1 elements (which has been used as parent for matroska_cluster, too) and
it affects recursive elements (currently only the SimpleTag), where the
non-recursive parent has to be choosen.

This is in preparation for a patch that redoes level handling.

Finally, the segment id has been added to ebml_syntax. This will enable
handling of unknown-length EBML headers.
Signed-off-by: Andreas Rheinhardt <andreas.rheinhardt@gmail.com>

Currently, resyncing during reading packets works as follows:
The current position is recorded, then a call to matroska_parse_cluster
is made and if said call fails, the demuxer tries to resync from the
earlier position. If the call doesn't fail, but also doesn't deliver a
packet, then this is looped.

There are two problems with this approach:
1. The Matroska file format aims to be forward-compatible; to achieve
this, a demuxer should simply ignore and skip elements it doesn't
know about. But it is not possible to reliably distinguish unknown
elements from junk. If matroska_parse_cluster encounters an unknown
element, it can therefore not simply error out; instead it returns zero
and the loop is iterated which includes an update of the position that
is intended to be used in case of errors, i.e. the element that is
skipped is not searched for level 1 element ids to resync to at all if
later calls to matroska_parse_cluster return an error.
Notice that in case that sync has been lost there can be a chain of
several unknown/possibly junk elements before an error is detected.

2. Even if a call to matroska_parse_cluster delivers a packet, this does
not mean that everything is fine. E.g. it might be that some of the
block's data is missing and that the data that was presumed to be from
the block just read actually contains the beginning of the next element.
This will only be apparent at the next call of matroska_read_packet,
which uses the (false) end of the earlier block as resync position so
that in the (not unlikely) case that the call to matroska_parse_cluster
fails, the data believed to be part of the earlier block is not searched
for a level 1 element to resync to.

To counter this, a "last known good" position is introduced. When an
element id that is known to be allowed at this position in the hierarchy
(according to the syntax currently in use for parsing) is read and some
further checks (regarding the length of the element and its containing
master element) are passed, then the beginning of the current element is
treated as a "good" position and recorded as such in the
MatroskaDemuxContext. Because of 2., only the start of the element is
treated as a "good" position, not the whole element. If an error occurs
later during parsing of clusters, the resync process starts at the last
known good position.

Given that when the header is damaged the subsequent resync never skips over
data and is therefore unaffected by both issues, the "last known good"
concept is not used there.
Signed-off-by: Andreas Rheinhardt <andreas.rheinhardt@gmail.com>

Since the changes to the parsing of SimpleBlocks, both ebml_parse_id and
ebml_parse_elem are only called from one place, so that it is possible
to inline these two function calls. This is done, but not completely:
ebml_parse_id still exists in a modified form. This is done in
preparation for a further patch regarding the handling of
unknown-length elements.
Signed-off-by: Andreas Rheinhardt <andreas.rheinhardt@gmail.com>

The earlier code set the level to zero upon seeking and after a
discontinuity although in both cases parsing (re)starts at a level 1
element.

Also set the segment's length to unkown if an error occured in order not
to drop any valid data that happens to be beyond the designated end of
the segment.
Signed-off-by: Andreas Rheinhardt <andreas.rheinhardt@gmail.com>

This function will be useful later to reset the status (e.g. current
level and the already parsed id).
Signed-off-by: Andreas Rheinhardt <andreas.rheinhardt@gmail.com>

When an error happens, the Matroska demuxer tries to resync to level 1
elements from an earlier position onwards. If the seek to said earlier
position fails, the demuxer currently treats this as an unrecoverable
error. And that behaviour is suboptimal as said failure is nothing
unrecoverable or unexpected (when the input isn't seekable).
It is preferable to simply resync from the earliest position available
(i.e. the start of the AVIOContext's buffer) onwards if the seek failed.

Here are some scenarios that might be treated as unrecoverable errors
by the current code if the input isn't seekable. They all have in
common that the current position is so far away from the desired
position that the seek can't be fulfilled from the AVIOContext's buffer:

1. Blocks (both SimpleBlocks as well as a Block in a BlockGroup) for
which reading them as binary EBML elements succeeds, but whose parsing
triggers an error (e.g. an invalid TrackNumber). In this case the
earlier position from which resyncing begins is at the start of the block
(or even earlier).
2. BlockGroups, whose parsing fails in one of the latter elements. Just
as in 1., the start of the BlockGroup (the target of the seek) might be
so far away from the current position that it is no longer in the
buffer.
3. At the beginning of parsing a cluster, the cluster is parsed until a
SimpleBlock or a BlockGroup is encountered. So if the input is damaged
between the beginning of the cluster and the first occurrence of a
SimpleBlock/BlockGroup and if said damage makes the demuxer read/skip so
much data that the beginning of the cluster is no longer in the buffer,
demuxing will currently fail completely.
Signed-off-by: Andreas Rheinhardt <andreas.rheinhardt@gmail.com>

The field was removed years ago.
Signed-off-by: James Almer <jamrial@gmail.com>

Tested-by: Michael Niedermayer <michael@niedermayer.cc>
Signed-off-by: Steven Liu <lq@chinaffmpeg.org>

fix ticket: 8015

Reported-by: Jun Zhao
Signed-off-by: Steven Liu <lq@chinaffmpeg.org>

Add missing documentation for nointra.
Reviewed-by: Michael Niedermayer <michael@niedermayer.cc>
Signed-off-by: Jun Zhao <barryjzhao@tencent.com>

Fixes: signed integer overflow: 32 * 538976288 cannot be represented in type 'int'
Fixes: 15633/clusterfuzz-testcase-minimized-ffmpeg_DEMUXER_fuzzer-5752273981931520

Found-by: continuous fuzzing process https://github.com/google/oss-fuzz/tree/master/projects/ffmpegReviewed-by: Paul B Mahol <onemda@gmail.com>
Signed-off-by: Michael Niedermayer <michael@niedermayer.cc>

Fixes: left shift of 133 by 24 places cannot be represented in type 'int'
Fixes: 15365/clusterfuzz-testcase-minimized-ffmpeg_DEMUXER_fuzzer-5716153105645568

Found-by: continuous fuzzing process https://github.com/google/oss-fuzz/tree/master/projects/ffmpegSuggested-by: Reimar Döffinger <Reimar.Doeffinger@gmx.de>
Reviewed-by: Reimar Döffinger <Reimar.Doeffinger@gmx.de>
Signed-off-by: Michael Niedermayer <michael@niedermayer.cc>

Reviewed-by: Peter Ross <pross@xvid.org>
Signed-off-by: Michael Niedermayer <michael@niedermayer.cc>

The dump_extra bitstream filter currently simply adds the extradata to
the packets indicated by the user without checking whether said
extradata already exists in the packets. Besides wasting space
duplicated extradata in the same packet/access unit is also forbidden
for some codecs, e.g. MPEG-2.

This check has been added to be able to use the mpeg2_qsv encoder (which
only adds the sequence headers to the first packet) in broadcast
scenarios where repeating sequence headers are required.

The check used here is not perfect: E.g. dump_extra would add the
extradata to a H.264 access unit consisting of an access unit delimiter,
SPS, PPS and slices.

Fixes #8007.
Signed-off-by: Andreas Rheinhardt <andreas.rheinhardt@gmail.com>
Signed-off-by: Michael Niedermayer <michael@niedermayer.cc>

Fixes non-monotonous timestamps.

Fixes non-monotonous timestamps.

Fixes non-monotonous timestamps.

It's better to do it before the buffers are actually created. At least in VLC
we currently don't support changing some parameters dynamically easily so we
don't use the information if it comes after the buffer are created.
Co-authored-by: James Almer <jamrial@gmail.com>
Signed-off-by: James Almer <jamrial@gmail.com>

It's better to do it before the buffers are actually created. At least in VLC
we currently don't support changing some parameters dynamically easily so we
don't use the information if it comes after the buffer are created.
Co-authored-by: James Almer <jamrial@gmail.com>
Signed-off-by: James Almer <jamrial@gmail.com>

Fixes non-monotonous timestamps.

Current version of dvbsub encoder doesn't support HD DVB subtitles. The high
resolution bitmaps are muxed into the stream but without the DDS (display definition
segment) the players asume that the DVB subtitles are in SD (720x576) resolution
which causes them to either render the subtitles too large and misplaced or don't
render them at all. By including the DDS as defined in section 7.7.1 of ETSI EN 300
743 (V1.3.1) this problem is fixed.

7.2.1 Display definition segment The display definition for a subtitle service may
be defined by the display definition segment if present in the stream. Absence of a
DDS implies that the stream is coded in accordance with EN 300 743 (V1.2.1) [5] and
that a display width of 720 pixels and a display height of 576 lines may be assumed.

https://www.etsi.org/deliver/etsi_en/300700_300799/300743/01.03.01_60/en_300743v010301p.pdfSigned-off-by: Jernej Fijacko <mikrohard@gmail.com>
Signed-off-by: Marton Balint <cus@passwd.hu>

Signed-off-by: Andreas Rheinhardt <andreas.rheinhardt@gmail.com>
Signed-off-by: James Almer <jamrial@gmail.com>