[FFmpeg-trac] #1607(avformat:new): av_seek_frame() without AVSEEK_FLAG_ANY on mpg files returns success without seeking to a keyframe

[FFmpeg]

#1607: av_seek_frame() without AVSEEK_FLAG_ANY on mpg files returns success
without seeking to a keyframe
------------------------------------+------------------------------------
             Reporter:  mbradshaw   |                    Owner:
                 Type:  defect      |                   Status:  new
             Priority:  normal      |                Component:  avformat
              Version:  git-master  |               Resolution:
             Keywords:              |               Blocked By:
             Blocking:              |  Reproduced by developer:  0
Analyzed by developer:  0           |
------------------------------------+------------------------------------

Comment (by mbradshaw):

 Replying to [comment:4 cehoyos]:
 > Replying to [comment:3 DonMoir]:
 > > mpeg2video failing sample file (6 MB):
 > >
 > > http://sms.pangolin.com/temp/mpeg2video_seek_to_non_keyframe.mpg
 > I failed to extract a non-keyframe out of this sample with ffmpeg.
 > If it is possible, please provide the command together with complete,
 uncut console output.
 Can you describe how you were able to extract only keyframes out of this
 sample? Because I'm afraid we may not be on the same page (again). If
 `av_seek_frame()` seeks to a keyframe, then the first packet out of
 `av_read_frame()` should be a keyframe packet and the first call to
 `avcodec_decode_video2()` with this packet should return a full decoded
 frame. This is not the case. `av_seek_frame()` on this file (and other mpg
 files) seeks to a non-keyframe, and the first several packets out of
 `av_read_frame()` are not keyframe packets, and several calls must be made
 to `avcodec_decode_video2()` before a full decoded frame is returned.

 The problem isn't that you get a junk frame out (the decoder makes sure
 you don't). The problem is that `av_seek_frame()` doesn't seek to a
 keyframe packet (despite the fact that that's what it claims it does), and
 several calls must be made to `av_read_frame()` before finally finding a
 keyframe packet.

-- 
Ticket URL: <https://ffmpeg.org/trac/ffmpeg/ticket/1607#comment:5>
FFmpeg <http://ffmpeg.org>
FFmpeg issue tracker