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QuickTime 4 API Documentation

QuickTime 4 Reference

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The Compression Parameters Structure

These new fields have been added to the compression parameters structure originally documented in Inside Macintosh: QuickTime Components .

struct CodecCompressParams
{
...
    /* The following fields are defined in QuickTime 2.1 or later */
    UInt16                      majorSourceChangeSeed;
    UInt16                      minorSourceChangeSeed;
    CDSequenceDataSourcePtr     sourceData;

    /* The following field is defined in QuickTime 2.5 or later */
    long                        preferredPacketSizeInBytes;

    /* The following fields are defined in QuickTime 3 or later */
    long                        requestedBufferWidth;
    long                        requestedBufferHeight;
}

Field description

majorSourceChangeSeed
Contains an integer value that is incremented each time a data source is added or removed. This provides a fast way for a codec to know when it needs to redetermine which data source inputs are available.

minorSourceChangeSeed
Contains an integer value that is incremented each time a data source is added or removed, or the data contained in any of the data sources changes. This provides a way for a codec to know if the data available to it has changed.

sourceData
Contains a pointer to a CDSequenceDataSource structure. This structure contains a linked list of all data sources. Because each data source contains a link to the next data source, a codec can access all data sources from this field.

preferredPacketSizeInBytes
Specifies the preferred packet size for data.

requestedBufferWidth
Specifies the the width of the image buffer to use, in pixels. For this value to be used, the codecWantsSpecialScaling flag in the CodecCapabilities record must be set.

requestedBufferHeight
Specifies the the height of the image buffer to use, in pixels. For this value to be used, the codecWantsSpecialScaling flag in the CodecCapabilities record must be set.

© 1999 Apple Computer, Inc.

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