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Andreas Rheinhardt a3db9f62a4 avformat/matroskadec: Introduce a "last known good" position 
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>
2019-07-16 16:16:58 -03:00
compat compat/cuda/ptx2c: don't drop final newline 2019-05-24 19:23:39 +02:00
doc doc/codecs: Add missing documentation for nointra 2019-07-15 09:21:33 +08:00
ffbuild Merge commit '7e5bde93a1e7641e1622814dafac0be3f413d79b' 2019-03-10 19:31:13 -03:00
fftools ffmpeg_opt: Respect default disposition when select audio/video 2019-07-03 10:33:44 +08:00
libavcodec avcodec: remove reference to AVPacket's destruct field 2019-07-15 11:20:03 -03:00
libavdevice lavd/avfoundation: Set correct default value 0 for option capture_raw_data. 2019-07-08 20:02:41 +02:00
libavfilter avfilter/vf_hysteresis: use time_base from framesync 2019-07-14 19:14:10 +02:00
libavformat avformat/matroskadec: Introduce a "last known good" position 2019-07-16 16:16:58 -03:00
libavresample
libavutil avutil/hwcontext_vaapi: move kernel_driver into CONFIG_LIBDRM 2019-07-11 09:34:57 +08:00
libpostproc
libswresample swresample/swresample: check for invalid sample rates 2019-05-26 14:43:32 +02:00
libswscale swscale/tests/swscale: Lengthen pixfmt name buffer to 21 bytes 2019-05-13 13:39:49 +02:00
presets
tests fate: add hls fmp4 segment type test case 2019-07-15 21:57:43 +08:00
tools tools/target_dec_fuzzer: Remove redundant av_free() 2019-07-13 14:42:57 +02:00
.gitattributes
.gitignore tools/python: add script to convert TensorFlow model (.pb) to native model (.model) 2019-07-01 10:23:47 -03:00
.travis.yml Merge commit '899ee03088d55152a48830df0899887f055da1de' 2019-03-14 15:53:16 -03:00
Changelog avformat/movenc: use unspecified language by default 2019-07-12 20:26:38 +02:00
configure avutil/mips: optimize UNPCK&SAD macros with MSA2.0 instruction. 2019-07-10 12:54:57 +02:00
CONTRIBUTING.md
COPYING.GPLv2
COPYING.GPLv3
COPYING.LGPLv2.1
COPYING.LGPLv3
CREDITS
INSTALL.md
LICENSE.md LICENSE: Clarify --enable-nonfree. 2019-05-10 01:18:58 +02:00
MAINTAINERS MAINTAINERS: remove myself as mailing list maintainer 2019-03-21 11:34:13 -08:00
Makefile tools: Add fuzzer for demuxers 2019-05-31 22:44:30 +02:00
README.md
RELEASE

README.md

FFmpeg README

FFmpeg is a collection of libraries and tools to process multimedia content such as audio, video, subtitles and related metadata.

Libraries

  • libavcodec provides implementation of a wider range of codecs.
  • libavformat implements streaming protocols, container formats and basic I/O access.
  • libavutil includes hashers, decompressors and miscellaneous utility functions.
  • libavfilter provides a mean to alter decoded Audio and Video through chain of filters.
  • libavdevice provides an abstraction to access capture and playback devices.
  • libswresample implements audio mixing and resampling routines.
  • libswscale implements color conversion and scaling routines.

Tools

  • ffmpeg is a command line toolbox to manipulate, convert and stream multimedia content.
  • ffplay is a minimalistic multimedia player.
  • ffprobe is a simple analysis tool to inspect multimedia content.
  • Additional small tools such as aviocat, ismindex and qt-faststart.

Documentation

The offline documentation is available in the doc/ directory.

The online documentation is available in the main website and in the wiki.

Examples

Coding examples are available in the doc/examples directory.

License

FFmpeg codebase is mainly LGPL-licensed with optional components licensed under GPL. Please refer to the LICENSE file for detailed information.

Contributing

Patches should be submitted to the ffmpeg-devel mailing list using git format-patch or git send-email. Github pull requests should be avoided because they are not part of our review process and will be ignored.