QuickTime Layers - Core Animation - page 125

LISTING 7-10

Continued

// Try to open the device
[videoDevice open:&error];

// No need to continue if device couldn't be opened
if ( error != nil ) return ;

// Create a device input object to add to the capture session
QTCaptureDeviceInput *input =
[[QTCaptureDeviceInput alloc ]
initWithDevice:videoDevice];
[captureSession addInput:input error:&error];

if ( error != nil ) return ;

// Create video output to add raw frames to the session
output = [[QTCaptureDecompressedVideoOutput alloc ] init ];
[captureSession addOutput:output error:&error];

if ( error != nil ) return ;

[ self setSession:captureSession];

}

}

This relatively small amount of code is quite amazing in what it provides. This abstrac-
tions Apple enables you to easily capture and display frames in real time. With
QTCaptureSession created, the next thing to do is obtain a frame at any given time
by setting a delegate for the QTCaptureDecompressedVideoOutput object. After the
QTCaptureDecompressedVideoOutput object has been allocated, set its delegate to self
using the following:

[output setDelegate:self];

This enables you to capture the output as an image file or to a QuickTime movie object.
First, however, let's take a closer look at how QTCaptureLayer was initialized for the
capture session.

Creating and Displaying the QTCaptureLayer
Although it is possible to create a QTCaptureLayer object directly with alloc and init , or
with a convenience function such as +layerWithSession , we're going to subclass
QTCaptureLayer so that we can hide QTCaptureSession 's initialization in the init . We do