Developer Documentation

QuickTime 4 API Documentation

Inside Macintosh: QuickTime Components

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Previewing

Previewing captured data involves playing that data for the user as it is digitized. For video data, this means displaying the video images on the computer screen. For audio data, this means playing the sound through the computer's sound system. The following paragraphs outline the steps the sequence grabber component follows to preview captured data.

  1. First, the sequence grab ber component opens a connection to your channel component, using the Component Manager's OpenComponent function. The sequence grabber component then calls your SGInitChannel function to initialize your component. For more on SGInitChannel , see SGInitChannel .
  2. The sequence grabber component then configures your channel component for the preview operation. The SGSetGWorld function (described on SGSetGWorld ) sets the graphics world in which the preview is to be displayed. The SGSetChannelUsage function (described on SGSetChannelUsage ) specifies that your channel is to be used for previewing. The application can then use the appropriate channel configuration functions to prepare your channel for the preview operation. For video channels, it uses the functions discussed in "Configuration Functions for Video Channel Components," . For sound channels, the sequence grabber uses the functions discussed in "Configuration Functions for Sound Channel Components," .
  3. The sequence grabber component starts the preview operation by calling your SGStartPreview function (described on SGStartPreview ). The sequence grabber component then begins collecting data from all of the channels participating in the preview and plays that data appropriately. The sequence grabber component can pause and restart the preview by calling the SGPause function (described on SGPause ). The sequence grabber component uses the SGStop function (described on SGStop ) to stop the preview. During the preview operation, the sequence grabber component calls your SGIdle function (described on SGIdle ) frequently, so that your channel can perform its operation.
  4. When the application is done previewing, the sequence grabber component can start recording or close its connection to your component.
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