[FFmpeg-trac] #1575(documentation:new): Clarify docs that av_seek_frame() may possibly not seek by keyframe

[FFmpeg]

#1575: Clarify docs that av_seek_frame() may possibly not seek by keyframe
-------------------------------------+-------------------------------------
               Reporter:  mbradshaw  |                  Owner:  stefano
                   Type:             |                 Status:  new
  enhancement                        |              Component:
               Priority:  normal     |  documentation
                Version:  git-       |               Keywords:
  master                             |               Blocking:
             Blocked By:             |  Analyzed by developer:  0
Reproduced by developer:  0          |
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 As a result of the [http://ffmpeg.org/pipermail/libav-
 user/2012-July/002468.html discussion on the libav-user mailing list]
 ([http://ffmpeg.org/pipermail/libav-user/2012-July/002510.html
 particularly this reply]), I learned that `av_seek_frame()` may  not
 actually seek by keyframe for some files. The way the current
 documentation is ("Seek to the keyframe at timestamp.") it sounds like it
 will always seek to a keyframe, which implies the next packet read and fed
 into `avcodec_decode_video2/audio4()` will result in a complete frame,
 which of course is not the case if seeking by keyframe is not done.

 This ticket is a request to simply expand on the existing documentation of
 `av_seek_frame()` and clarify that seeking may possibly not be done by
 keyframe (and any other gotchas that people might know that aren't
 documented with `av_seek_frame()`). I'd submit a patch myself but I seem
 to always get surprised with new gotchas when it comes to seeking, so I
 hope someone who is more familiar with `av_seek_frame()`'s behavior can
 better expound than I can.

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Ticket URL: <https://ffmpeg.org/trac/ffmpeg/ticket/1575>
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