[FFmpeg-trac] #5093(undetermined:reopened): Accurate seek not possible with MPEG program stream and transport sream

[FFmpeg]

#5093: Accurate seek not possible with MPEG program stream and transport sream
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             Reporter:  pkerling     |                    Owner:
                 Type:  enhancement  |                   Status:  reopened
             Priority:  normal       |                Component:
              Version:  unspecified  |  undetermined
             Keywords:               |               Resolution:
             Blocking:               |               Blocked By:
Analyzed by developer:  0            |  Reproduced by developer:  0
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Changes (by pkerling):

 * status:  closed => reopened
 * resolution:  invalid =>


Comment:

 I've looked into the reason for this behaviour, and it seems that with
 MPEG PS and TS the initial seek is done based on the AVIndexEntry entries
 which are not accurate. Because the PES header does not include whether
 the video frame is a key frame or not, the MPEG demuxer marks every frame
 as keyframe (See the call to av_add_index_entry in mpegps_read_pes_header,
 libavformat/mpeg.c). The seek code then thinks it's ok to seek there even
 if it's really a B frame and does not try to search for a preceding
 keyframe which would normally be necessary. The video decoder throws away
 everything up to the next keyframe so this is what gets written to the PNG
 file in the end.
 After all, I do think this is a bug, so I'm reopening the ticket. Feel
 free to close it again if this is really the way it should be.

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Ticket URL: <https://trac.ffmpeg.org/ticket/5093#comment:4>
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