QuickTime 4 Reference

About the Text Channel Component

The QuickTime text channel component allows an application to obtain text from an external source. Once obtained, this text can be previewed or recorded into a QuickTime movie. The source of the text is unknown to the text channel component; a text digitizer component ('tdig' ) is responsible for acquiring the text from the external source. The text channel component is provided by QuickTime.

Text digitizers are separate components; they are the mechanism for presenting new sources of text data to QuickTime. Several text digitizer components are available, including one that captures closed-captioned data using an Apple TV Tuner card. For more information on creating a component, see the chapter "Component Manager" in Mac OS For QuickTime Programmers.

To retrieve text for previewing or for recording in a QuickTime movie, the application uses the text channel the same way in which it would use a video channel. The application calls a sequence grabber component, which, in turn, calls the text channel component. The text channel component calls the appropriate text digitizer component to retrieve the text. For more information on how to use sequence grabber components, see the chapter "Sequence Grabber Components" in Inside Macintosh: QuickTime Components.

Once text has been retrieved, the application can request that the sequence grabber component store the text in a text track of a QuickTime movie. For more information on the text media handler, see chapter "Movie Toolbox" in Inside Macintosh: QuickTime.

The QuickTime text channel component supports some, but not all, functions defined for sequence grabber channel components and sequence grabber panel components. The supported functions are described in Table 1 .

In addition, the text channel component provides new functions implemented specifically for text; you use these functions to format captured text to be viewed or added to a text track of a movie. The new functions are described in "Text Channel Component Reference" .

Table 1 Functions supported by the text channel component
Usage	Supported
General sequence grabber component functions	`SGSetGWorld`
	`SGNewChannel`
	`SGStartPreview`
	`SGStartRecord`
	`SGIdle`
	`SGStop`
	`SGPause`
	`SGPrepare`
	`SGRelease`
	`SGGetChannelDeviceList`
	`SGUpdate`
Functions for getting and setting channel characteristics	`SGSetChannelUsage`
	`SGGetChannelUsage`
	`SGSetChannelBounds`
	`SGGetChannelBounds`
	`SGGetChannelInfo`
	`SGSetChannelClip`
	`SGGetChannelClip`
	`SGGetChannelSampleDescription`
	`SGSetChannelDevice`
	`SGSetChannelMatrix`
	`SGGetChannelMatrix`
	`SGGetChannelTimeScale`
Text channel component functions called by sequence grabber components	`SGInitChannel`
	`SGWriteSamples`
	`SGGetDataRate`
Sequence grabber panel component functions	`SGPanelGetDitl`
	`SGPanelInstall`
	`SGPanelEvent`
	`SGPanelRemove`
	`SGPanelGetSettings`
	`SGPanelSetSettings`
	`SGPanelItem`