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Currently, ff_frame_thread_free() uses the last worker thread to updates the first worker thread via update_context_from_thread() immediately before freeing all these worker threads. This is a remnant of the time in which the first worker was special. (E.g. the first worker shared its AVCodecInternal with the public AVCodecContext.) But these times are over (none of the uses of is_copy matter for ff_frame_thread_free()); nowadays the only thing that update_context_from_thread() does is referencing a few buffers/frames and replacing them with other references instead. These new references will then be freed immediately thereafter when the first worker thread is freed. Ensuring that the code is free of double-frees is achieved by using reference-counted structures (or in case of AVChannelLayouts: by giving each worker its own copy). Some archaeology: a) Updating the first worker thread from the last one used has been done since frame-threading was added in37b00b47cb. b) The precursor to ff_mpv_common_end() checked for is_copy before freeing pictures (i.e. it only freed them for the first worker thread). c) Commitsc2dfb1e37cande33811bd26modified the update_thread_context function of the H.264 decoder so that it could fail before calling ff_mpeg_update_thread_context(). d) This led to a double free/an assert violation with a H.264 sample for which ff_mpeg_update_thread_context() is not reached for the final update_context_from_thread(). Commita6e4796fbfadded code to fix this sample. e) This issue was fixed (even with the last mentioned commit reverted) when the H.264 decoder was deMpegEncContextized in commitb7fe35c9e5(merging commit2c54155407). f) mpegvideo.c stopped using is_copy when it was switched to refcounted frames in759001c534. g)1f4cf92cfbremoved the init_thread_copy callbacks; now no FFCodec.close callback checks for is_copy at all any more. 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.