[FFmpeg-trac] #4437(avdevice:new): AVFoundation recording has consistent intermittent frame drops

[FFmpeg]

#4437: AVFoundation recording has consistent intermittent frame drops
-------------------------------------+-------------------------------------
             Reporter:  LordHDL      |                     Type:  defect
               Status:  new          |                 Priority:  normal
            Component:  avdevice     |                  Version:  git-
             Keywords:               |  master
  avfoundation                       |               Blocked By:
             Blocking:               |  Reproduced by developer:  0
Analyzed by developer:  0            |
-------------------------------------+-------------------------------------
 '''Summary''': 60 FPS screen capture on OS X results in intermittent drops
 every 5-8 seconds.
 '''How to reproduce''': Record a video with AVFoundation using `-framerate
 60`.
 {{{
 ffmpeg -f avfoundation -pix_fmt 0rgb -framerate 60 -video_device_index 3
 -i “” -c:v libx264rgb -crf 0 -vf crop=426:240:507:339
 ~/Desktop/avfoundation.avi
 }}}

 Additional notes:

 * I have a SATA 3 SSD; plenty of disk write speed.
 * The source does not drop frames during recording, only the video does.
 * The source frame rate is exactly 60 FPS.
 * The frame drops have a fairly consistent timing.
 * Recording the same source in Windows does not produce these frame drops.
 * Media players will report an average rate of around 57.13 (it varies).
 * The `-r 60` output option will of course force the rate to 60, but not
 prevent the frame drops.
 * Example recording:
 https://www.dropbox.com/s/0dthf652g644ldq/avfoundation.avi.xz?dl=0

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Ticket URL: <https://trac.ffmpeg.org/ticket/4437>
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