Inside Macintosh: QuickTime Components /

Chapter 8 - Video Digitizer Components / Video Digitizer Components Reference

Video Digitizer Component Functions / Controlling Compressed Source Devices

VDGetCompressionTypes

The VDGetCompressionTypes function allows an application to determine the image-compression capabilities of the video digitizer.

pascal VideoDigitizerError VDGetCompressionTypes 
                           (VideoDigitizerComponent ci,
                           VDCompressionListHandle h);

ci

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

h

Identifies a handle to receive the compression information. The video digitizer returns information about its capabilities by formatting one or more compression list structures in this handle (the format and content of the compression list structure are discussed later). If the digitizer supports more than one compression type, it creates an array of structures in this handle.

The video digitizer sizes this handle appropriately. It is the application's responsibility to dispose of this handle when it is done with it.

DESCRIPTION

The video digitizer places its preferred, or default, compression options in the first compression list structure in the returned array.

Note that there must be a decompressor component of the appropriate type available in the system if an application is to display images from a compressed image sequence.

The VDCompressionList data type defines the format and content of the compression list structure:

typedef struct VDCompressionList {
   CodecComponent    codec;         /* component ID */
   CodecType         cType;         /* compressor type */
   Str63             typeName;      /* compression algorithm */
   Str63             name;          /* compressor name string */
   long              formatFlags;   /* data format flags */
   long              compressFlags; /* capabilities flags */
   long              reserved;      /* set to 0 */
} VDCompressionList, *VDCompressionListPtr, 
**VDCompressionListHandle;

Field Description

codec

Contains the component identifier for the video digitizer's compressor component. Some video digitizers may also implement their image-compression capabilities in an Image Compression Manager compressor component. In this case, the digitizer may allow the application to connect to and use the compressor. If so, the digitizer provides the compressor component's identifier here. If not, the digitizer sets this field to nil.

cType

Identifies the compression algorithm supported by the video digitizer. See the chapter "Image Compression Manager" in Inside Macintosh: QuickTime for a list of values supported by Apple.

typeName

Contains a text string that identifies the compression algorithm. An application may display this string to the user to identify the type of image compression being performed. See the chapter "Image Compression Manager" in Inside Macintosh: QuickTime for a list of values supported by Apple.

name

Specifies the name of the compressor. The developer of the video digitizer assigns this name. An application may display this string to the user.

formatFlags

Contains flags that describe the data formats supported by the video digitizer. Typically, these flags are of interest only to developers of video digitizers and image compressors. See the chapter "Image Compressor Components" in this book for more information.

compressFlags

Contains flags that describe the compression capabilities of the video digitizer. Typically, these flags are of interest only to developers of video digitizers and image compressors. See the chapter "Image Compressor Components" in this book for more information.

reserved

Reserved for Apple. Always set to 0.

RESULT CODES

noErr	0	No error
digiUnimpErr	-2201	Function not supported

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