AVCaptureSession preset photo and AVCaptureVideoPreviewLayer size - objective-c

Question

I initialize an AVCaptureSession and I preset it like this :
AVCaptureSession *newCaptureSession = [[AVCaptureSession alloc] init];
if (YES==[newCaptureSession canSetSessionPreset:AVCaptureSessionPresetPhoto]) {
newCaptureSession.sessionPreset = AVCaptureSessionPresetPhoto;
} else {
// Error management
}
Then I setup an AVCaptureVideoPreviewLayer :
self.preview = [[UIView alloc] initWithFrame:CGRectMake(0, 0, self.view.frame.size.width, self.view.frame.size.height/*426*/)];
CALayer *previewLayer = preview.layer;
AVCaptureVideoPreviewLayer *captureVideoPreviewLayer = [[AVCaptureVideoPreviewLayer alloc] initWithSession:self.session];
captureVideoPreviewLayer.frame = previewLayer.frame;
[previewLayer addSublayer:captureVideoPreviewLayer];
captureVideoPreviewLayer.videoGravity = AVLayerVideoGravityResizeAspect;
My question is:
How can I get the exact CGSize needed to display all the captureVideoPreviewLayer layer on screen ? More precisely I need the height as AVLayerVideoGravityResizeAspect make the AVCaptureVideoPreviewLayer fits the preview.size ?
I try to get AVCaptureVideoPreviewLayer size that fit right.
Very thank you for your help

Answer 1

After some research with AVCaptureSessionPresetPhoto the AVCaptureVideoPreviewLayer respect the 3/4 ration of iPhone camera. So it's easy to have the right height with simple calculus.
As an instance if the width is 320 the adequate height is:
320*4/3=426.6

Answer 2

Weischel's code didn't work for me. The idea worked, but the code didn't. Here's the code that did work:
// Get your AVCaptureSession somehow. I'm getting mine out of self.videoCamera, which is a GPUImageVideoCamera
// Get the appropriate AVCaptureVideoDataOutput out of the capture session. I only have one session, so it's easy.
AVCaptureVideoDataOutput *output = [[[self.videoCamera captureSession] outputs] lastObject];
NSDictionary* outputSettings = [output videoSettings];
// AVVideoWidthKey and AVVideoHeightKey did not work. I had to use these literal keys.
long width = [[outputSettings objectForKey:#"Width"] longValue];
long height = [[outputSettings objectForKey:#"Height"] longValue];
// video camera output dimensions are always for landscape mode. Transpose if your camera is in portrait mode.
if (UIInterfaceOrientationIsPortrait([self.videoCamera outputImageOrientation])) {
long buf = width;
width = height;
height = buf;
}
CGSize outputSize = CGSizeMake(width, height);

Answer 3

If I understand you correctly, you try to get width & height of the current video session.
You can obtain them from the outputSettings dictionary of your AVCaptureOutput. (Use AVVideoWidthKey & AVVideoHeightKey).
e.g.
NSDictionary* outputSettings = [movieFileOutput outputSettingsForConnection:videoConnection];
CGSize videoSize = NSMakeSize([[outputSettings objectForKey:AVVideoWidthKey] doubleValue], [[outputSettings objectForKey:AVVideoHeightKey] doubleValue]);
Update:
Another idea would be to grab the frame size from the image buffer of the preview session.
Implement the AVCaptureVideoDataOutputSampleBufferDelegate method captureOutput:didOutputSampleBuffer:fromConnection:
(don't forget to set the delegate of your AVCaptureOutput)
- (void)captureOutput:(AVCaptureFileOutput*)captureOutput didOutputSampleBuffer:(CMSampleBufferRef)sampleBuffer fromConnection:(AVCaptureConnection*)connection
{
CVImageBufferRef imageBuffer = CMSampleBufferGetImageBuffer(sampleBuffer);
if(imageBuffer != NULL)
{
CGSize imageSize = CVImageBufferGetDisplaySize(imageBuffer);
NSLog(#"%#", NSStringFromSize(imageSize));
}
}

Answer 4

Thanks to gsempe for your answer. I'm on the same problem since hours :)
And i solved it with this code, to center it in the screen in landscape mode :
CGRect layerRect = [[[self view] layer] bounds];
[PreviewLayer setBounds:CGRectMake(0, 0, 426.6, 320)];
[PreviewLayer setPosition:CGPointMake(CGRectGetMidY(layerRect), CGRectGetMidX(layerRect))];
Note that I had to invert the CGRectGetMidY() and CGRectGetMidX() function to have a centered layer into my screen.
Thanks,
Julian