[FFmpeg-devel] [RFC] fftools/ffmpeg and libavdevice/sdl issue

[Anton Khirnov]

Quoting Zhao Zhili (2023-12-12 18:27:39)
> Now it's time to talk about the libavdevice/sdl issue.
> 
> SDL output is broken with ffmpeg multithread refactor. SDL 'muxer' write_header
> and write_packet must be run in the same thread. And to make it work portable
> and reliable, SDL 'muxer' must be run in main thread. It's a common requirement
> for render to be run in main thread.
> 
> There are at least two trac tickets for the same issue: #10644 and #10649.
> 
> And there are two patches for the issue:
> https://patchwork.ffmpeg.org/project/ffmpeg/patch/20230918063728.198377-1-haihao.xiang@intel.com/
> https://patchwork.ffmpeg.org/project/ffmpeg/patch/20231101090115.10655-1-angus.chen@intel.com/
> 
> There patches might work on Linux, but not portable.
> 
> A simple workaround is pipe the output of ffmpeg to ffplay:
> 
> ./ffmpeg -re -i /e/video/cctv.mp4 -an -f yuv4mpegpipe - |ffplay -
> 
> To fix it, another thread can be used to drive transcode rather than main thread.
> A main loop should be created on main thread, and prepared to handle any special
> tasks like render. It sounds a lot of work. I'm not sure if it worth for a single use case.
> However, maybe we can have a libavfilter/vsink_preview after that.
> 
> What should we do?

Honestly I don't see how this could be done in ffmpeg CLI without
disgusting hacks, but before that the question is: why is there an SDL
"muxer" and why would anyone want to use it in ffmpeg CLI? What actual
use cases does it serve that cannot be better handled otherwise?

-- 
Anton Khirnov