Inside Macintosh: QuickTime Components /

Chapter 8 - Video Digitizer Components / Video Digitizer Components Reference

Video Digitizer Component Functions / Controlling Compressed Source Devices

VDCompressDone

The VDCompressDone function allows an application to determine whether the video digitizer has finished digitizing and compressing a frame of image data. An application starts the digitizing process by calling the VDCompressOneFrameAsync function, which was just discussed.

pascal VideoDigitizerError VDCompressDone 
                           (VideoDigitizerComponent ci, 
                            Boolean *done, Ptr *theData, 
                            long *dataSize, 
                            unsigned char *similarity, 
                            TimeRecord *t);

ci

Identifies the application's connection to the video digitizer component. An application obtains this value from the Component Manager's OpenComponent function.

done

Contains a pointer to a Boolean value. Applications set this value to true when they are done, and set it to false if the operation is incomplete.

theData

Contains a pointer to a field that is to receive a pointer to the compressed image data. The digitizer returns a pointer that is valid in the application's current memory mode.

The digitizer allocates the memory into which it places the digitized data. An application must call the VDReleaseCompressBuffer function to dispose of this memory; this function is discussed next.

dataSize

Contains a pointer to a field to receive a value indicating the number of bytes of compressed image data.

similarity

Contains a pointer to a field to receive an indication of the relative similarity of this image to the previous image in a sequence. A value of 0 indicates that the current frame is a key frame in the sequence. A value
of 255 indicates that the current frame is identical to the previous frame. Values from 1 through 254 indicate relative similarity, ranging from very different (1) to very similar (254). This field is only filled in if the temporal quality passed in with the VDSetCompression function (described on page 8-44) is not 0--that is, if it is not frame-differenced.

t

Contains a pointer to a time record. When the operation is complete, the digitizer fills in this structure with information indicating when the frame was grabbed. The time value stored in this structure is in the time base that the application sets with the VDSetTimeBase function (see page 8-51 for more information about this function). The format and content of this structure are discussed in the chapter "Movie Toolbox" in Inside Macintosh: QuickTime.

DESCRIPTION

An application can determine when the digitizer is done with the frame by calling the VDCompressDone function. When the digitizer is done, it sets the Boolean value referred to by the done parameter to true, and then returns information about the digitized and compressed frames via the theData, dataSize, similarity, and
t parameters.

If the digitizer is not yet done, it sets the Boolean value to false. In this case, the digitizer does not return any other information.

Note that the digitizer is careful to return the frames in temporal order, and to avoid returning two frames with the same time value (unless the rate is set to 0).

RESULT CODES

noErr	0	No error
digiUnimpErr	-2201	Function not supported

SEE ALSO

Applications must use the VDReleaseCompressBuffer function to free the memory that contains the compressed image data. This function is described in the next section.

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