Programming iOS 6, 3rd Edition

Image Capture With AV Foundation

Instead of using UIImagePickerController, you can control the camera and capture images using the AV Foundation framework (Chapter 28). You get no help with interface (except for displaying in your interface what the camera “sees”), but you get far more detailed control than UIImagePickerController can give you; for example, for stills, you can control focus and exposure directly and independently, and for video, you can determine the quality, size, and frame rate of the resulting movie. You can also capture audio, of course.

The heart of all AV Foundation capture operations is an AVCaptureSession object. You configure this and provide it as desired with inputs (such as a camera) and outputs (such as a file); then you call startRunning to begin the actual capture. You can reconfigure an AVCaptureSession, possibly adding or removing an input or output, while it is running — indeed, doing so is far more efficient than stopping the session and starting it again — but you should wrap your configuration changes in beginConfiguration and commitConfiguration.

As a rock-bottom example, let’s start by displaying in our interface, in real time, what the camera sees. This requires an AVCaptureVideoPreviewLayer, a CALayer subclass. This layer is not an AVCaptureSession output; rather, the layer receives its imagery by owning the AVCaptureSession:

self.sess = [AVCaptureSession new]; AVCaptureDevice* cam = [AVCaptureDevice defaultDeviceWithMediaType:AVMediaTypeVideo]; ...