ScheduledFrameCompleted frequency.

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ZachAnderson

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ScheduledFrameCompleted frequency.

PostTue Jun 12, 2018 1:15 pm

We are using ScheduleVideoFrame for sending video frames to the DeckLink card. We have been relying on the frequency of the callback for synchronization for a 50fps stream, with the callback occurring every 20ms.

This has been working well for us, until we discovered that on occasion the callback would come after somewhere between 40 and 60ms, causing a synchronization event to occur, producing artifacts in the output. Following this large gap, the callback would occur more frequently than 20ms for several frames, eventually getting back to the correct callback times and intervals.

Looking through other posts in the forum, I found a couple things to check for that may impact the callback. The first is that at least 2 frames should be pre-rolled for 4k video. We are pre-rolling 3 frames, and as a test I tried pre-rolling 8 and 10 frames, but still had this issue.

The second is to make sure the callback function does not take longer than the amount of time it takes to display a frame. Again the display time is 20ms, and the function only runs for at most about 1ms, so there should not be an issue there either.

Should we be able to depend on the frequency of the callback function for our synchronization? If so, is there anything else I can be looking at that can cause the callback to be late?

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