[FFmpeg-trac] #1578(undetermined:new): variable FPS incorrect frame length

FFmpeg trac at avcodec.org
Fri Jul 27 09:37:01 CEST 2012

#1578: variable FPS incorrect frame length
             Reporter:  kubabrecka   |                     Type:  defect
               Status:  new          |                 Priority:  normal
            Component:               |                  Version:
  undetermined                       |  unspecified
             Keywords:               |               Blocked By:
  fps,framerate,vfr,qtrle            |  Reproduced by developer:  0
             Blocking:               |
Analyzed by developer:  0            |
 I have a sample video to reproduce this bug - see attachment.

 The video is in Apple Animation codec (qtrle) with variable frame rate and
 contains only 5 frames. Frames 1,2,4 and 5 are displayed for a very short
 time, but frame 3 is much longer.

 When I extract all the frames into PNGs with this command:

 ./ffmpeg -vsync 2 -i apple-animation-variable-fps-bug.mov -vf
 "[in]showinfo[out]" out/img%04d.png

 it's fine, I get 5 PNG files, and the timestamps shown on the output are

 n:0 pts:0 pts_time:0 pos:48
 n:1 pts:600 pts_time:0.2 pos:4335
 n:2 pts:1300 pts_time:0.433333 pos:8286
 n:3 pts:7300 pts_time:2.43333 pos:12518
 n:4 pts:8100 pts_time:2.7 pos:16642

 as you can see, frame n:2 (the third frame) is displayed for much longer
 than the others. However, when I run this command to dump the frames with
 a constant FPS:

 ./ffmpeg -i apple-animation-variable-fps-bug.mov -r 30 out/img%04d.png

 the frames are dumped with wrong timing. The "long" frame was 2 seconds
 long, so it should be in about 60 frames (with FPS 30), but instead it
 only gets 7 frames. But the next frame which should be very short is
 dumped into 60 frames. It seems that the conversion between variable FPS
 into constant FPS incorrectly assigns frame length into the next frame.

Ticket URL: <https://ffmpeg.org/trac/ffmpeg/ticket/1578>
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