QuickTime 4 Reference

Creating a Sequence Grabber Component that Captures Multiple Files

You can create a sequence grabber component that can capture to multiple files by doing the following in your sequence grabber component:

Use SGAddExtendedMovieData rather than SGAddMovieData to write data.
In the SGWriteSamples routine, instead of using SGGetNextFrameReference , use SGGetNextExtendedFrameReference .

An example of how to do this is shown in Listing 1 . This example also shows how to use the SGAddOutputDataRefToMedia helper routine to easily manage the multiple files in which the captured data is stored.

Listing 1 Channel capture and managing multiple output files



 
Track aTrack = NewMovieTrack(theMovie, width, height, 0);

Media aMedia = NewTrackMedia(aTrack, TextMediaType,

                        kMediaTimeScale, nil, 0);

SeqGrabExtendedFrameInfo fi;

SGOutput lastOutput = nil;

long i;

OSErr err;

fi.frameChannel = store->self;

i = -1;

do {

    TimeValue frameDuration;

    err = SGGetNextExtendedFrameReference(store->grabber, &fi,

            &frameDuration, &i);

            if (err) {

                if (err == paramErr)

                err = noErr;

                break;

            }

    // switch to the next data reference

    if (lastOutput != fi.frameOutput) {

        err = SGAddOutputDataRefToMedia(store->grabber,

            fi.frameOutput, aMedia, sampleDescription);

        if (err) goto exit;

        lastOutput = fi.frameOutput;

    }

    //note that only the low 32 bits of the file offset are used here

    err = AddMediaSampleReference(aMedia,

            fi.frameOffset.lo, fi.frameSize,

            frameDuration,

            sampleDescription, 1,

            0, 0);

} while (err == noErr);

exit:

    if (alias) DisposeHandle((Handle)alias);

    return err;

In this example, the default data reference is not defined when NewTrackMedia is called. Instead, the default data reference is defined by the first call to SGAddOutputDataRefToMedia . This approach provides added flexibility by allowing movies to be captured to data handlers other than the standard file system data handler.