gistfile1.m

  // Derive dimensions of the capture device input.
  AVCaptureInputPort *captureDeviceInputPort = nil;
  for (AVCaptureInputPort *port in [captureDeviceInput ports]) {
    if ([[port mediaType] isEqualToString:AVMediaTypeVideo]) {
      captureDeviceInputPort = port;
      break;
    }
  }
  if (!captureDeviceInputPort) {
    NSLog(@"Capture device input port of video media type was "
          @"unexpectedly not found.");
    NSLog(@"Skipping.");
    return;
  }
  CMFormatDescriptionRef formatDescription =
      [captureDeviceInputPort formatDescription];
  CMVideoDimensions videoDimensions =
      CMVideoFormatDescriptionGetDimensions(formatDescription);
  [self willChangeValueForKey:@"inputSize"];
  inputSize = CGSizeMake(
      (CGFloat)videoDimensions.width, (CGFloat)videoDimensions.height);
  [self didChangeValueForKey:@"inputSize"];
  NSLog(@"Derived device input size: %@", NSStringFromCGSize(inputSize));