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The HEVC decoder has both HEVCContext and HEVCLocalContext structures. The latter is supposed to be the structure containing the per-slicethread state. Yet that is not how it is handled in practice: Each HEVCLocalContext has a unique HEVCContext allocated for it and each of these coincides with the main HEVCContext except in exactly one field: The corresponding HEVCLocalContext. This makes it possible to pass the HEVCContext everywhere where logically a HEVCLocalContext should be used. This led to confusion in the first version of what eventually became commitc8bc0f66a8: Before said commit, the initialization of the Rice parameter derivation state was incorrect; the fix for single-threaded as well as frame-threaded decoding was to add backup stats to HEVCContext that are used when the cabac state is updated*, see https://ffmpeg.org/pipermail/ffmpeg-devel/2020-August/268861.html Yet due to what has been said above, this does not work for slice-threading, because the each HEVCLocalContext has its own HEVCContext, so the Rice parameter state would not be transferred between threads. This is fixed inc8bc0f66a8by a hack: It rederives what the previous thread was and accesses the corresponding HEVCContext. Fix this by treating the Rice parameter state the same way the ordinary CABAC parameters are shared between threads: Make them part of the same struct that is shared between slice threads. This does not cause races, because the parts of the code that access these Rice parameters are a subset of the parts of code that access the CABAC parameters. *: And if the persistent_rice_adaptation_enabled_flag is set. 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.