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Important: This document contains legacy content. Apple recommends that developers explore AV Foundation and Core Video for new development in this technology area. See AV Foundation Framework Reference for Mac and Core Video Programming Guide for more information.

Text Channel Components

Text channel components are a type of sequence grabber channel component. A text channel component captures text for use in QuickTime movies. It is controlled by a sequence grabber component. Applications programmers will normally interact with the higher-level sequence grabber component, and do not need to read this chapter.

Text channel components make use of text digitizer components, which digitze text from particular sources, such as the closed-caption text from a video input. Text channel components abstract this level of detail, allowing the sequence grabber component to work with a stream of text without regard to its source.

You should read this chapter if you are developing a text channel component, a text digitizer, or a sequence grabber component.

About the QuickTime 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.

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.

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.

Text Channel Component Functions

The following channel component functions are unique to text channel components. These functions allow captured text to be formatted prior to being previewed or added to a movie.

SGSetFontName
SGSetFontSize
SGSetTextForeColor
SGSetTextBackColor
SGSetJustification
SGGetTextReturnToSpaceValue
SGSetTextReturnToSpaceValue

The QuickTime text channel component also supports some, but not all, functions defined for sequence grabber channel components and sequence grabber panel components. The supported functions are the following:

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

For further information about these functions, see Sequence Grabber Component Functions.

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