Save sampleBuffer in array (AVFoundation)

Question

I try to save the sample buffer instead of an UIImage to an array, to convert it later on. This to speed up the image capturing and maybe not get memory warnings. I just can't figure out how to save it to the array and then use it again to call [self imageFromSampleBuffer:sampleBuffer]. I tried something like this, but how do I convert the data back to a CMSampleBufferRef object?

- (void)captureOutput:(AVCaptureOutput *)captureOutput 
    didOutputSampleBuffer:(CMSampleBufferRef)sampleBuffer 
   fromConnection:(AVCaptureConnection *)connection { 
// Create a UIImage from the sample buffer data
//      UIImage *image = [self imageFromSampleBuffer:sampleBuffer];
//      [arrCaptures addObject:image];

[arrImageBuffer addObject:[NSData dataWithBytes:sampleBuffer length:sizeof(sampleBuffer)] ];}

Icydog · Accepted Answer · 2011-10-06 17:12:05Z

5

Why not just use a CFArray and directly put the CMSampleBufferRef objects in there?

answered Oct 6, 2011 at 17:12

Icydog

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10 Comments

Snilleblixten Over a year ago

Thanks, well I can't really figure out how to do that. I tried to put it in an NSValue object and ALMOST got it working. I guess I got some homework to do.

Icydog Over a year ago

Try making a CFMutableArray and then doing CFArrayAppendValue(arr, sampleBuffer). developer.apple.com/library/mac/documentation/CoreFoundation/…

Snilleblixten Over a year ago

It seems to work to store with CFArrayAppendValue(arrCFImageBuffer, sampleBuffer); But after I don't find the way to get it back. This doesn't work: CMSampleBufferRef imageBuffer = CFArrayGetValueAtIndex(arrCFImageBuffer, currImageIdx);

Icydog Over a year ago

What do you mean by "doesn't work"; i.e. what's the problem? Does it crash? You may need to cast the return value like CMSampleBufferRef imageBuffer = (CMSampleBufferRef)CFArrayGetValueAtIndex(arrCFImageBuffer, currImageIdx); and also be sure to provide kCFTypeArrayCallBacks as the third argument to CFArrayCreateMutable.

Eimantas Over a year ago

@Snilleblixten - that's because AVFoundation uses pool of 13 (in your case) preallocated CMSampleBuffer instances and recycles them. Since you're adding them to the array, they get retained and not released back to the pool. You have to create a copy of the CMSampleBuffer (CMSampleBufferCopy creates shallow copy, so it won't work) and then release the buffer back to the pool.

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Yaron Recher · Accepted Answer · 2013-07-06 12:36:25Z

4

You can use CFArray but you should remember that the CMSampleBufferRef is not retained, and that the "captureOutput:didOutputSampleBuffer:fromConnection:" uses a memory pool - and when you don't release the memory it stops sending new samples (that is why you get only 13 samples) as you can read in:captureOutput:didOutputSampleBuffer:fromConnection:

answered Jul 6, 2013 at 12:36

Yaron Recher

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