Capture device playback on Mac dropped frames & clock/timestamp sync errors
I find VLC on Mac cannot play video+audio from a Capture Device properly. I do File - Open Capture Device, and select my hdmi capture card's Video and Audio devices. The video will play but with lots of dropped frames (very choppy video). The audio is ok.
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These messages are logged repeatedly in the VLC log: clock gap, unexpected stream discontinuity feeding synchro with a new reference point trying to recover from clock gap Timestamp conversion failed (delay 300000, buffering 0, bound 9000000) Could not convert timestamp 2255674958149 for rawvideo
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The capture card is a UVC device playing 1080p@50fps content.
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I am using a USB 3 port and a USB 3 5Gpbs cable.
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I have an alternate player on OS X that works perfectly. I get full frame rate with perfect audio. This tells me it cannot be a hardware issue.
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I've tried two different capture cards. Same problem on both. (One Magewell, one EVGA XR1 lite). This tells me it's not specific to the card.
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The same capture cards work perfectly with VLC on Windows. This is a Mac specific issue.
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I tested both cards on a Mac Mini and a Macbook Pro, with Mojave and Catalina. Same problem on both.
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If I select only the video device in File - Open Capture Device (no audio) it plays perfectly (without sound). It seems this is a clock/timestamp issue synchronising the audio with the video
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I'm running VLC 3.0.17.3 (Intel 64bit). I also tried the 3.x and 4.x nightlies which give the same problem.
I think VLC must have a problem playing content from AVFoundation/AVCapture.