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ddf8f40301
The capture callback dropped the previous frame instead of waiting for it
to be consumed, so frames were lost when avf_read_packet() fell behind;
39fbd06314 (return EAGAIN instead of waiting) made it easy to hit.
Add back a condition variable: the capture callback blocks until
avf_read_packet() takes the current frame, and the reader waits on it when
no frame is ready. An is_stopping flag set in destroy_context() wakes both
sides so teardown cannot deadlock. observed_quit is now set under the lock
and broadcast as well, so a blocked reader wakes and returns EOF when a
transport-control device stops delivering frames.
Based on a patch by Zhongxin Zhuang <zx.zhuang@hotmail.com>; here
unlock_frames() only broadcasts and unlocks, so a read no longer releases
the other stream's still-unconsumed frame.
Verified by capturing camera+mic for 8s and comparing delivered packet
counts before/after this change:
ffmpeg -f avfoundation -pixel_format nv12 -framerate 30 -i "0:0" -t 8 \
-vf "scale=2560:1440,hqdn3d" -c:v libx264 -preset medium \
-c:a aac out.mp4
ffprobe -count_packets -show_entries stream=nb_read_packets out.mp4
slow consumer (ideal: video ~240, audio ~375)
video audio
before (EAGAIN) 174 163 (audio ~57% dropped)
after (condvar) 234 376 (no drops)
fast consumer (-preset ultrafast, no filter)
before 240 328
after 238 376
Signed-off-by: Jun Zhao <barryjzhao@tencent.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.