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The GetVideoPortBandwidthcallback function informs clients of bandwidth requirements for any specified format, helping them to chose a format and better understand its limitations. This information can only be given after the video port object is created because the information in the DDVIDEOPORTDESCstructure is required before accurate bandwidth information can be supplied. This callback is required.
DWORD __stdcall GetVideoPortBandwidth( LPDDHAL_GETVPORTBANDWIDTHDATA pgvpbd );
Returns one of the following values:
The available bandwidth for some devices depends primarily on the amount of pre-scaling and on the amount that the overlay is zoomed. The available bandwidth for other devices depends primarily on the source size of the overlay. This function supports both types of devices.
If this function is called with the DDVPB_TYPEflag set in the DDHAL_GETVPORTBANDWIDTHDATAstructure, the HAL should indicate which type of device it is by setting the DDVPBCAPS_SOURCEor DDVPBCAPS_DESTINATIONflags in the DDVIDEOPORTBANDWIDTHstructure. The DDVPBCAPS_SOURCEsize indicates that the bandwidth depends on the overlay source size, and the DDVPBCAPS_DESTINATIONsize indicates that the bandwidth depends on the overlay destination size.
When this function is called with the DDVPB_VIDEOPORTflag set, the dwWidth and dwHeight members in the DDHAL_GETVPORTBANDWIDTHDATAstructure refer to the video port pre-scale parameters. The HAL should return the overlay stretch factors at which it is possible to perform the various levels of support (1X = 1000, 2X = 2000, and so on). This flag assumes that the device is best described using the DDVPBCAPS_DESTINATIONflag. If this is not the case, the HAL should fail the call.
When this function is called with the DDVPB_OVERLAYflag set, the dwWidth and dwHeight members in the DDHAL_GETVPORTBANDWIDTHDATAstructure refer to the overlay source size, and the HAL should return the percentage of the original overlay size required to perform the various levels of support (none = 1000, 3/4 = 750, and so on) This flag assumes that the device is best described using the DDVPBCAPS_SOURCEflag. If this is not the case, the HAL should fail the call.
Last updated on Tuesday, July 13, 2004