You've already forked FFmpeg
mirror of
https://github.com/FFmpeg/FFmpeg.git
synced 2025-08-15 14:13:16 +02:00
31741aecbf
HWAccels with frame threads are fundamentally flawed in avcodecs current design, and there are several known problems ranging from image corruption to driver crashes. These problems come down to two design problems in the interaction of threads and HWAccel decoding: (1) While avcodec prevents parallel decoding and as such simultaneous access to the hardware accelerator from the decoding threads, it cannot account for the user code and its access to the hardware surfaces and the hardware itself. This can result in image corruption or even driver crashes if the user code locks image surfaces while they are being used by the decoder threads as reference frames. The current HWAccel API does not offer any way to ensure exclusive access to the hardware or the surfaces if frame threading is used. (2) Initialization of the HWAccel with frame threads is non-trivial, and many decoders had and still have issues that cause excess calls to the get_format callback. This will potentially cause duplicate HWAccel initialization, which in extreme cases can even lead to driver crashes if the HWAccel is re-initialized while the user code is actively accessing the hardware surfaces associated with it, or lead to image corruption due to lost reference frames. While both of these issues are solvable, fixing (1) would at least require a huge API redesign which would move a lot of complexity into the user code. The only reason the combination of frame threads and HWAccel was considered useful is to allow a seamless fallback to multi-threaded software decoding if the HWAccel is not available, however the issues outlined above far outweigh this. The proper solution for a fallback is to re-open the AVCodecContext with threading enabled if the HWAccel failed, which is a practice commonly used by various user applications using avcodec today already. Reviewed-by: Gwenole Beauchesne <gb.devel@gmail.com> Reviewed-by: wm4 <nfxjfg@googlemail.com> Signed-off-by: Hendrik Leppkes <h.leppkes@gmail.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 a mean to alter decoded Audio and Video through chain of 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.
- ffserver is a multimedia streaming server for live broadcasts.
- 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. Few developers
follow pull requests so they will likely be ignored.