[FFmpeg-trac] #11467(avformat:new): FIFO Muxer: restart_with_keyframe recovers on audio packets

[FFmpeg]

#11467: FIFO Muxer: restart_with_keyframe recovers on audio packets
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             Reporter:  Wallboy     |                     Type:  defect
               Status:  new         |                 Priority:  normal
            Component:  avformat    |                  Version:  7.1
             Keywords:  fifo muxer  |               Blocked By:
             Blocking:              |  Reproduced by developer:  0
Analyzed by developer:  0           |
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 Summary of the bug:

 When using restart_with_keyframe in the FIFO muxer, I believe the
 expectation is that packets are dropped until the next **video** keyframe.
 The current behavior is that it will recover if it also encounters any
 audio packet, as they are flagged as a keyframe.

 If this is the expected behavior, then perhaps an additional option should
 be added to FIFO to allow resumption only on video keyframes as well. This
 is particularly useful if you are reconnecting to an RTMP server and wish
 to make sure you're sending a keyframe first and not a B/P frame.

 How to reproduce:

 Start a local ffmpeg RTMP server:
 {{{
 ffmpeg -f flv -listen 1 -i rtmp://127.0.0.1/app/path -f null /dev/null
 }}}

 Create a test source and output to local RTMP server:

 {{{
 ffmpeg -loglevel repeat+verbose -re -f lavfi -i
 "testsrc=duration=600:size=640x360:rate=30" -f lavfi -i
 "sine=frequency=1000:duration=600" -c:v libx264 -pix_fmt yuv420p -f fifo
 -fifo_format flv -attempt_recovery 1 -restart_with_keyframe 1
 -drop_pkts_on_overflow 1 -map 0:v -map 1:a -flags +global_header
 rtmp://127.0.0.1/app/path
 }}}

 **NOTE:** drop_pkts_on_overflow must be set to 1 here, otherwise frames
 will not be dropped until keyframe. (See my other newly created ticket for
 this issue: https://trac.ffmpeg.org/ticket/11466)

 Attach to the second ffmpeg using your debugger of choice and set a
 breakpoint on this line:
 https://github.com/FFmpeg/FFmpeg/blob/dc7964a862890d58072ee9ca711b4b38eda5a209/libavformat/fifo.c#L193

 Stop the ffmpeg server (Ctrl+C), so that the FIFO muxer goes into recovery
 mode. Then start the server back up and wait for FIFO to reconnect and hit
 the breakpoint. Notice any audio packets received at this point will be
 considered a keyframe, and hence will resume sending audio/video packets
 from that point on.
-- 
Ticket URL: <https://trac.ffmpeg.org/ticket/11467>
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