CMSampleBufferGetSampleTimingInfo: No duration?

Question

I have a live stream, and CMSampleBufferGetSampleTimingInfo gives a duration with CMTime(value=0, timescale=0) for video.

For audio, I get 1024 samples at once, but CMSampleBufferGetSampleTimingInfo(sampleBuffer, index, &timingInfo) gives the exact same presentationTimeStamp for every single index in the sample.

How can I accurately get duration info during a live stream for video frames, and how can I get the actual time of an audio sample in a CMSampleBufferRef?

score 1 · Accepted Answer · answered Nov 22 '15 at 22:00

1

You can only rely on presentationTimeStamps, so you can't know the duration of the current video frame until the next frame arrives. This makes sense for a live stream, as capture frame rates are variable and depend on lighting, etc, but this also seems to be true when the sample buffers come from a file.

The duration can be calculated like so:

CMTimeSubtract(timingInfoNext.presentationTimeStamp, timingInfoCurrent.presentationTimeStamp)

answered Nov 22 '15 at 22:00

Rhythmic Fistman

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I guess this makes sense, but it makes other math harder. The average duration between frames may be enough for my needs. – Stefan Kendall Nov 22 '15 at 22:53

CMSampleBufferGetSampleTimingInfo: No duration?

1 Answers1