[FFmpeg-trac] #11055(avcodec:reopened): OGOP (Open GOP) in certain conditions may cause missing frames of decoding

[FFmpeg]

#11055: OGOP (Open GOP) in certain conditions may cause missing frames of decoding
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             Reporter:  markfilipak  |                    Owner:  (none)
                 Type:  defect       |                   Status:  reopened
             Priority:  normal       |                Component:  avcodec
              Version:  git-master   |               Resolution:
             Keywords:  everything   |               Blocked By:
  OGOP                               |
             Blocking:               |  Reproduced by developer:  0
Analyzed by developer:  0            |
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Comment (by pdr0):

 Replying to [comment:203 Balling]:
 > "pdr0 & Balling at
 > trac.ffmpeg.org hint that key frames are specific I-frames"
 >
 > Keyframes are only when you clean start from it. In Open GOP by
 definition you can have a situation where some after I frames or its
 slices you can have dependence on frames before that I frame, thus that is
 non IDR frame/slice. Moroover, some frames can still be cleanly decoded
 even though we have that and are marked as recovery frames with
 exact_match=1 like in your example, moreover some frames are tagged as
 just recovery that allows to get after some frames to the same stream .
 >
 > See, for example, https://bitmovin.com/vvc-open-gop-resolution-switching



 For an encoded stream, yes, - that's the whole point of using open GOP

 But not when you edit  . When the 2nd segment does not start with IDR ,
 there is no reset to frame_num . You get the problems that you see here

 e.g.

 If you have frame_num 0,1,2,3,4 for part a , but 3,4,5,6 for part b
 (because not on IDR) , the frame_num decreases from 4 to 3 in decoding
 order this is a clear spec violation
-- 
Ticket URL: <https://trac.ffmpeg.org/ticket/11055#comment:205>
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