QuickTime 4 Reference

Using Image Transcoder Components

The Image Compression Manager uses an image sequence when compressing or decompressing data. An image sequence allows QuickTime to make certain optimizations because it knows that a similar operation will be repeated multiple times (that is, images will be repeatedly compressed to the same image data format). Similarly, the Image Compression Manager's support for image transcoding is based on an image transcoding sequence. The image transcode sequence identifier is an opaque value as shown below.



 
typedef long ImageTranscodeSequence;

All transcoding functions called by applications are described in Chapter 3, "Image Compression Manager." Image transcoder component functions are described later in this chapter.

To create an image transcoding sequence, use the ImageTranscodeSequenceBegin function. To transcode a frame of image data, use the ImageTranscodeFrame function. The caller of this routine is responsible for disposing of the transcoded data returned by ImageTranscodeFrame using the ImageTranscodeDisposeFrameData routine.

When the transcoded image data returned by ImageTranscodeFrame is no longer needed, call ImageTranscodeDisposeFrameData to dispose of the data. When an image transcoding sequence is complete, use ImageTranscodeSequenceEnd to dispose of the image transcoding sequence.