Append buffers to an AVAssetWriterInputPixelBufferAdaptor *not* chronologically?

I'm appending CVPixelBufferRefs to an AVAssetWriterInputPixelBufferAdaptor which is connected to an AVAssetWriterInput to write to a file using AVAssetWriter.
So, I'm calling
Code Block
[pixelAdaptor appendPixelBuffer:pxbuffer withPresentationTime:someCMTime];

and it works as it should.

Now, I'm doing this sequentially, so at CMTimeZero, I add the first frame, at time 0.5s I append another frame, at 1s another, and so on, and so on.

I'm wondering, do I have to do it sequentially, or can I do it randomly as well? For the sake of argument, the other way around? Like, append a buffer at 1s first, then at 0.5s and then at 0s?

The reason I'm asking is, I've tried, and it crashes, but I'm not sure if it crashes because I tried to append at random times (non-sequentially), or if there's another reason (like asynchronous appending)?

I'm only appending when the input tells me to (readyForMoreMediaData), on a serial dispatch queue.
The question is: Should non-sequential appending work, or is it by design that it doesn't?

Thank you,
Matthias
Answered by Media Engineer in 639316022
AVAssetWriter requires receiving the frames in order.
Accepted Answer
AVAssetWriter requires receiving the frames in order.
thank you, much appreciated!
I am curious though about what exactly happens when you tried non-sequential frames. You say it crashes, do you actually mean that AVAssetWriter throws an exception? Or some other crash? I ask because ideally AVAssetWriter would make it clear that non-sequential append is not supported, rather than failing in an ambiguous way.
Append buffers to an AVAssetWriterInputPixelBufferAdaptor *not* chronologically?
 
 
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