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Inside Macintosh: QuickTime Components

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Previewing

Previewing captured data involves playing that data for the user as it is captured. 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 you must follow to preview captured data.

1. First, you must open a connection to the sequence grabber component. Use the Component Manager's OpenDefaultComponent or OpenComponent function.
2. Once you have a connection to a sequence grabber component, you must configure the component for the preview operation. Use the SGSetGWorld function (described on SGSetGWorld ) to set the graphics world in which the preview is to be displayed. Allocate the appropriate channels by calling the SGNewChannel function (described on SGNewChannel ). You must call this function once for each channel to be used by the sequence grabber component. Use the SGSetChannelUsage function (described on SGSetChannelUsage ) to specify that each channel is to be used for previewing. You can then use the appropriate channel configuration functions to prepare the channel for the preview operation. For video channels, use the functions discussed in "Working With Video Channels," . For sound channels, use the functions discussed in "Working With Sound Channels," .
3. You start the preview operation by calling the SGStartPreview function (see SGStartPreview ). The sequence grabber component then begins collecting data from the channels that you have created and plays that data appropriately. You can pause and restart the preview by calling the SGPause function (see SGPause ). Use the SGStop function (see SGStop ) to stop the preview. During the preview operation, be sure to call the SGIdle function (see SGIdle ) frequently, so that the sequence grabber and its channels can perform the operation.
4. When you are done previewing, you can start recording or close your connection to the sequence grabber component. When you close the sequence grabber component, it automatically disposes of the channels you created.

See the sample program in Listing 1 for an example of the preview operation.

Recording

During a record operation, a sequence grabber component collects the data it captures and formats that data into a QuickTime movie. During a record operation, the sequence grabber can also play the captured data for the user. However, the sequence grabber tries to prevent the playback from interfering with the quality of the recording process.

The following paragraphs discuss the steps you must follow to record captured data.

1. As with a preview operation, your application must establish a connection to a sequence grabber component. Use the Component Manager's OpenDefaultComponent or OpenComponent function.
2. Once you have a connection to a sequence grabber component, you must configure the component for the record operation. Use the SGSetGWorld function (see SGSetGWorld ) to set the graphics world in which the data is to be displayed. Allocate the appropriate channels by calling the SGNewChannel function (see SGNewChannel ). You must call this function once for each channel to be used by the sequence grabber component. Use the SGSetChannelUsage function (see SGSetChannelUsage ) to specify that each channel is to be used for recording. At this time, you can specify whether the sequence grabber is to play that channel's data while recording. You can then use the appropriate channel configuration functions to prepare the channel for the record operation. For video channels, use the functions discussed in "Working With Video Channels," . For sound channels, use the functions discussed in "Working With Sound Channels," .
3. You must specify a movie file for use by the sequence grabber during the record operation. Use the SGSetDataOutput function (see SGSetDataOutput ) to specify this movie file. This function also allows you to control whether the sequence grabber adds the movie resource to the movie file and whether it replaces existing data or appends the new movie to the file.
4. You can limit the amount of data that is captured during a record operation. The SGSetMaximumRecordTime function (see SGSetMaximumRecordTime ) establishes a time limit for the record operation. The SGSetChannelMaxFrames function (see SGSetChannelMaxFrames ) limits the number of frames of data that the sequence grabber collects from a specific channel.
5. You start the record operation by calling the SGStartRecord function (see SGStartRecord ). The sequence grabber component then begins collecting data from the channels you have created, stores the data in a QuickTime movie, and, optionally, plays that data appropriately. You can pause and restart the record process by calling the SGPause function (see SGPause ). During the record operation, be sure to call the SGIdle function (see SGIdle ) frequently, so that the sequence grabber and its channels can perform the operation. Use the SGStop function (see SGStop ) to stop recording. At this time, the sequence grabber saves the movie in your movie file, if you have chosen to do so.
6. When you are done recording, you can go back to previewing or close your connection to the sequence grabber component. When you close the sequence grabber component, it automatically disposes of the channels you created as well as any movies it has created.