Controlling Compressed Source Devices(IM: QC)

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Chapter 8 - Video Digitizer Components / Video Digitizer Components Reference

Controlling Compressed Source Devices
Some video digitizer components may provide functions that allow applications to work with digitizing devices that can provide compressed image data directly. Such devices allow applications to retrieve compressed image data without using the Image Compression Manager. However, in order to display images from the compressed data stream, there must be an appropriate decompressor component available to decompress the image data.
Video digitizers that can support compressed source devices set the digiOutDoesCompress flag to 1 in their capability flags (see "Capability Flags" beginning on page 8-14 for more information about these flags).
Applications can use the VDGetCompressionTypes function to determine the image-compression capabilities of a video digitizer. The VDSetCompression function allows applications to set some parameters that govern image compression.
Applications control digitization by calling the VDCompressOneFrameAsync function, which instructs the video digitizer to create one frame of compressed image data. The VDCompressDone function returns that frame. When an application is done with a frame, it calls the VDReleaseCompressBuffer function to free the buffer. An application can force the digitizer to place a key frame into the sequence by calling the VDResetCompressSequence function. Applications can turn compression on and off by calling VDSetCompressionOnOff.
Applications can obtain the digitizer's image description structure by calling the VDGetImageDescription function. Applications can set the digitizer's time base by calling the VDSetTimeBase function.
All of the digitizing functions described in this section support only asynchronous digitization. That is, the video digitizer works independently to digitize each frame. Applications are free to perform other work while the digitizer works on each frame.
The video digitizer component manages its own buffer pool for use with these functions. In this respect, these functions differ from the other video digitizer functions that support asynchronous digitization (see "Controlling Digitization" beginning on page 8-52 for more information about these functions).

Subtopics

VDGetCompressionTypes

VDSetCompression

VDSetCompressionOnOff

VDCompressOneFrameAsync

VDCompressDone

VDReleaseCompressBuffer

VDGetImageDescription

VDResetCompressSequence

VDSetTimeBase