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Dropped frames during synchronized playback

PostPosted: Wed Jan 13, 2021 11:16 am
by Flo Loferer
Some of our customers have been reporting image "flashes" occurring sometimes during playback.
So far I wasn't able to reproduce this myself using a DeckLink Duo in a cheesegrater Mac Pro and a Thunderbolt Shuttle.

I purchased an UltraStudio 4K Mini now and I'm finally able to reproduce the issue.
I'm now trying to narrow it down and I'm seeing that whenever there's a "flash frame" (really just one frame from somewhere earlier in the timeline, apparently something the BM devices has in its internal buffers still) the Blackmagic device is also reporting a dropped frame.

Looking at the timing I can see that the ScheduledFrameCompleted callback is called every ~ 33 milliseconds (I'm using a 29.97 fps output frame rate so that's perfect) but when the frame is dropped the call back is called already about ~ 17 milliseconds after the last successful ScheduledFrameCompleted call. Just mentioning this in case this is somehow relevant.

I really don't know how to troubleshoot this further and I'm hoping someone can help.
ScheduleVideoFrame does not return an error when scheduling the frames.

Does anyone have a pointer of what this could be related to?

Thanks and best regards,


Re: Dropped frames during synchronized playback

PostPosted: Mon Jan 18, 2021 8:50 am
by Flo Loferer
It would really be helpful to get a pointer.
Anyone from Blackmagic who can chime in here?