[FFmpeg-trac] #7787(documentation:new): Examples don't flush the decoder causing missing frames

[FFmpeg]

#7787: Examples don't flush the decoder causing missing frames
-------------------------------------+-------------------------------------
             Reporter:               |                     Type:  defect
  MichelRouzic                       |
               Status:  new          |                 Priority:  normal
            Component:               |                  Version:  git-
  documentation                      |  master
             Keywords:  examples     |               Blocked By:
  docs decoding                      |
             Blocking:               |  Reproduced by developer:  0
Analyzed by developer:  0            |
-------------------------------------+-------------------------------------
 Summary of the bug: The examples in doc/examples don't use
 av_read_frame()'s return properly which can cause them to fail to decode
 the last few frames. In the case of transcoding.c breaking out of the loop
 when av_read_frame() returns negative thus stopping further decoding is at
 fault:
 {{{
     while (1) {
         if ((ret = av_read_frame(ifmt_ctx, &packet)) < 0)
             break;
 }}}

 The decoder should be flushed which isn't being done here. It seems that
 all the examples are affected which is a serious problem for anyone (like
 me) trying to learn from them as it doesn't show us how to decode a stream
 properly.

 How to reproduce:
 After building the examples, using this video with numbered frames
 https://photosounder.com/misc/drop_loop_300_frames_360p.mp4 as test input
 and running this:
 {{{
 ./transcoding.exe drop_loop_300_frames_360p.mp4 transcoded.mp4
 }}}
 we can see that there are two frames missing at the end of the output
 video. Using the output video as input creates another video with two more
 frames missing. I tried other input files like a 1080p YouTube MP4 and
 ffprobe reported one frame missing in transcoding.c's transcoded video, so
 this seems to be a pretty universal problem.

--
Ticket URL: <https://trac.ffmpeg.org/ticket/7787>
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