iOS - CMSampleBufferRef is not being released from captureOutput:didOutputSampleBuffer:fromConnection - iphone

Question

I am capturing frames from the camera using the code:
- (void)captureOutput:(AVCaptureOutput *)captureOutput
didOutputSampleBuffer:(CMSampleBufferRef)sampleBuffer
:(AVCaptureConnection *)connection
{
// Create a UIImage from the sample buffer data
UIImage *image = [self imageFromSampleBuffer:sampleBuffer];
if(delegate && [delegate respondsToSelector:#selector(captureManagerCapturedFrame:withFrameImage:withFrameBuffer:)]) {
[delegate captureManagerCapturedFrame:self withFrameImage:image withFrameBuffer:sampleBuffer];
}
}
I am doing this because in the delegate method captureManagerCapturedFrame:withFrameImage:withFrameBuffer: I have a flag which tells the app to use either the returned uiimage OR the returned sampleBuffer.
The delegate method is:
- (void) captureManagerCapturedFrame:(AVCamCaptureManager *)captureManager
withFrameImage:(UIImage *)image
withFrameBuffer:(CMSampleBufferRef)frameBuffer {
if(_screen1) {
NSLog(#"Only display camera image\n");
}
else if(_screen2) {
//Enable IR
NSLog(#"Display AND Process camera image\n");
[self imageReconigitionProcessFrame:frameBuffer];
}
}
where imageReconigitionProcessFrame: is:
-(void)imageReconigitionProcessFrame:(CMSampleBufferRef)frameBuffer {
//CFRetain(frameBuffer);
MSImage *qry = [[MSImage alloc] initWithBuffer:frameBuffer orientation:AVCaptureVideoOrientationPortrait]; //MEMORY LEAK HERE???
qry = nil;
//CFRelease(frameBuffer);
}
This code effectively works. But here is my problem. When this code is run and profiled in instruments, I see a rapid increase in the overall bytes used, but the allocations profiler doesn't appear to increase. Nor do a see any 'leaks' using the leaks tool. But clearly, there is a rapid memory gain each time imageReconigitionProcessFrame: is called and the app crashes after a few seconds. When I set frameBuffer to nil, there is NO increase in memory (or course I also don't have the frame buffer to do any processing with).
I have tried transfering ownership of frameBuffer using CFRetain and CFRelease (commented out in the above code), but these don't seem to do anything either.
Does anyone have any idea where I could be leaking memory inside this function???
The method [[MSImage alloc] initWithBuffer: is form a third party SDK (Moodstocks, which is an awesome image recognition SDK) and it works just fine in their demos, so I don't think the problem is inside this function.

Answer 1

First of all, thanks for mentioning Moodstocks (I work for them): we're happy that you find our SDK useful!
To answer your question, I guess your code does indeed contain a leak: at the end of the imageReconigitionProcessFrame method, you should call [qry release]. The rule in Obj-C is quite simple: whenever you manually call alloc on an object, it should also be manually released!
That's BTW what is done in the Moodstocks SDK wrapper: if you look at the [MSScannerSession session: didOutputSampleBuffer:] method, you'll see that we do manually release the MSImage object after it's been processed.
As to why the profiler doesn't find this leak, I guess that it's due to the fact that leaks are analyzed every 10 seconds by default: in this case, the memory leak is so heavy (1280x720 frames, at 15+ FPS if you're on an iPhone 5, for 10 seconds: at least 130 MB leaked) that the code must crash before the first 10 seconds are reached.
Hope this helps!