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

FFmpeg trac at avcodec.org
Tue Apr 11 18:10:47 EEST 2017

#4437: AVFoundation recording has consistent intermittent frame drops
             Reporter:  LordHDL      |                    Owner:  mateo
                 Type:  defect       |                   Status:  open
             Priority:  normal       |                Component:  avdevice
              Version:  git-master   |               Resolution:
             Keywords:               |               Blocked By:
  avfoundation bounty                |  Reproduced by developer:  1
             Blocking:               |
Analyzed by developer:  0            |

Comment (by LordHDL):

 I wasn't aware at the time of posting this ticket, but I've recently
 learned about VFR, CFR, and how they relate to each other.  Based on my
 testing with other software, it seems I can only capture every frame
 properly when recording VFR, as CFR will guarantee that frames are lost as
 the sources in question (contrary to what I previously thought) are
 ''not'' a constant rate.  Their advertised rate is 60 but in practice the
 FPS always fluctuates, making CFR unreliable for recording.

 I believe recording with the native input frame rate as variable might be
 the solution (as it was in other software) but I haven't been able to test
 it.  I tried `-vsync 0` (input, output, and also both at once) but the
 resulting video is always considered constant.  How do I tell ffmpeg to
 use VFR for input (and really that should be the default behavior)?

Ticket URL: <https://trac.ffmpeg.org/ticket/4437#comment:44>
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