[FFmpeg-trac] #2245(avformat:closed): Speed difference when using -ss on similar MKVs when extracting frame image

[FFmpeg]

#2245: Speed difference when using -ss on similar MKVs when extracting frame image
-------------------------------------+------------------------------------
             Reporter:  eelco        |                    Owner:
                 Type:  enhancement  |                   Status:  closed
             Priority:  wish         |                Component:  avformat
              Version:  git-master   |               Resolution:  fixed
             Keywords:  h264 mkv     |               Blocked By:
             Blocking:               |  Reproduced by developer:  0
Analyzed by developer:  0            |
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Comment (by eelco):

 I indeed want to speed up the seeking, but the output should still be
 correct ;)

 When I try with the new option added (with git-master) on the 2245-slow-
 ss-dd.mkv sample it is indeed very fast, but generates a bunch of warnings
 and an completely empty output picture.

 {{{
 ...
 matroska,webm @ 0x101806600] File is broken, keyframes not correctly
 marked!
 [h264 @ 0x10281ea00] reference picture missing during reorder
     Last message repeated 3 times
 [h264 @ 0x10281ea00] Missing reference picture, default is 0
 [h264 @ 0x10281ea00] decode_slice_header error
 [h264 @ 0x10281f600] reference picture missing during reorder
     Last message repeated 2 times
 [h264 @ 0x10281f600] Missing reference picture, default is 65564
     Last message repeated 2 times
 [h264 @ 0x10281fc00] mmco: unref short failure
     Last message repeated 1 times
 [h264 @ 0x102820200] reference picture missing during reorder
 [h264 @ 0x102820200] Missing reference picture, default is 65568
 [h264 @ 0x102820800] reference picture missing during reorder
 [h264 @ 0x102820800] Missing reference picture, default is 65570
 [h264 @ 0x10281ea00] mmco: unref short failure
 [matroska,webm @ 0x101806600] Read error
 frame=    1 fps=0.0 q=0.0 Lsize=N/A time=00:00:00.04 bitrate=N/A dup=0
 drop=1
 video:393kB audio:0kB subtitle:0 global headers:0kB muxing overhead
 -100.005461%
 }}}

 Regarding the second sample (2245-slow-ss-dd.mkv), can you explain why the
 second keyframe (at 10.427s) was not used to generate the image at 11s? In
 the output is says
 {{{
 frame=    1 fps=0.5 q=0.0 Lsize=N/A time=00:00:00.04 bitrate=N/A dup=0
 drop=262
 }}}

 It seems to me that it dropped 262 frames. When using it on the first
 “slow” file (2245-slow-ss.mkv) however, it does seem to detect the
 keyframe and only drops 15 frames:
 {{{
 frame=    1 fps=0.0 q=0.0 Lsize=N/A time=00:00:00.04 bitrate=N/A dup=0
 drop=15
 }}}

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Ticket URL: <https://ffmpeg.org/trac/ffmpeg/ticket/2245#comment:6>
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