mirror of
https://git.ffmpeg.org/ffmpeg.git
synced 2026-10-24 02:09:03 +03:00
b772f5033c
vp8_mc_luma()/vp8_mc_chroma() derive the reference row to await from y_off, which includes the block's motion vector, and never floor it at 0, so a vector pointing above the frame makes the awaited row negative. For a 16x16 block the expression still bottoms out at 0 for any vector inside clamp_mv()'s +-16 px margin, which is why the omission is easy to miss. The split modes, however, predict 8- and 4-row blocks, where a much smaller vector suffices: at mb_y 0 with block_h 8, y_off -12 gives (3 - 12 + 8) >> 4 == -1, and with block_h 4, y_off -8 does. SPLITMV sub-vectors are moreover never clamped, and NEWMV deltas are applied after clamp_mv(), so larger vectors are reachable too. ff_thread_progress_await() returns as soon as progress >= n, and progress is initialised to -1 under frame threading, so a negative row is treated as already reached and no happens-before edge with the thread decoding the reference frame is established. emulated_edge_mc() nevertheless clamps the source rectangle and reads row 0 of the reference plane, i.e. the row is read without waiting for it to be written. Floor the awaited row at 0, the lowest row the subsequent read can touch. The floor only ever raises a negative row to 0, never above a row already awaited on the same frame, so it cannot introduce a stall. Fixes: unsynchronized cross-thread read of reference frame rows Fixes: IFu1maPxsZFJ Found-by: Mozilla's AI bot, reviewed and reported by Chun-Min Chang <cchang@mozilla.com> Signed-off-by: Michael Niedermayer <michael@niedermayer.cc>
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.