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use_intra_dc_vlc is currently kept in sync between frame threads in mpeg4_update_thread_context(), yet it is set when decoding blocks, i.e. after ff_thread_finish_setup(). This is a data race and therefore undefined behaviour. This race can be fixed easily by moving the variable from the context to the stack: use_intra_dc_vlc is only read in mpeg4_decode_block() and only if one is decoding an intra block. There are three callsites for this function: One in mpeg4_decode_partitioned_mb() which always sets use_intra_dc_vlc before the call and two in mpeg4_decode_mb(). One of these callsites is for intra blocks and use_intra_dc_vlc is set before it; the last callsite is for non-intra blocks, where use_intra_dc_vlc is ignored. So if it is used, it always uses a new value and can therefore be moved to the stack. The above also explains why this data race did not lead to FATE-test failures. Signed-off-by: Andreas Rheinhardt <andreas.rheinhardt@outlook.com>
FFmpeg README
FFmpeg is a collection of libraries and tools to process multimedia content such as audio, video, subtitles and related metadata.
Libraries
libavcodecprovides implementation of a wider range of codecs.libavformatimplements streaming protocols, container formats and basic I/O access.libavutilincludes hashers, decompressors and miscellaneous utility functions.libavfilterprovides means to alter decoded audio and video through a directed graph of connected filters.libavdeviceprovides an abstraction to access capture and playback devices.libswresampleimplements audio mixing and resampling routines.libswscaleimplements 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,ismindexandqt-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.