DXVA_TCoefSingle structure (dxva.h)

Artikel
04/01/2021

The DXVA_TCoefSingle structure is sent by the host decoder to the accelerator to specify IDCT coefficient values.

Syntax

typedef struct _DXVA_TCoefSingle {
  WORD  wIndexWithEOB;
  SHORT TCoefValue;
} DXVA_TCoefSingle, *LPDXVA_TCoefSingle;

Members

wIndexWithEOB

This member contains two fields: TCoefIDX and TCoefEOB.

TCoefIDX

Specifies the scan index of the coefficient in the block, as determined from the bConfigHostInverseScan member of the DXVA_ConfigPictureDecode structure. This field is in the 15 most significant bits of the wIndexWithEOB member.

There are two ways that TCoefIDX can be used:

Run-length ordering: When bConfigHostInverseScan is zero, the MBscanMethod element of the macroblock control command indicates a zigzag, alternate-vertical, or alternate-horizontal inverse scan. These macroblock control commands are defined in the following structures: DXVA_MBctrl_I_OffHostIDCT_1 or DXVA_MBctrl_P_OffHostIDCT_1. In this case, TCoefIDX contains the number of zero-valued coefficients that precede the current coefficient in the specified scan order, subsequent to the last transmitted coefficient for the block (or relative to the start of the block if none precede it). Any remaining coefficients after the last sent coefficient in the inverse-scan order are implied to have the value zero.
Arbitrary ordering: When bConfigHostInverseScan is 1, the MBscanMethod element of the macroblock control command indicates arbitrary ordering. These macroblock control commands are defined in the following structures: DXVA_MBctrl_I_OffHostIDCT_1 and DXVA_MBctrl_P_OffHostIDCT_1. In this case, TCoefIDX simply contains the raster index of the coefficient within the block (TCoefIDX = u + 8 * v, where u and v are the transform-domain horizontal and vertical frequency coordinates), and any coefficients that are not sent are implied to have the value 0.

TCoefIDX must always be less than 64.

TCoefEOB

Indicates whether the current coefficient is the last one associated with the current block of transform coefficients. A value of 1 indicates that the current coefficient is the last one for the block and a value of zero indicates that it is not. This field is in the least significant bit of the wIndexWithEOB member.

TCoefValue

Indicates the value of the coefficient in the block. TCoefValue must be clipped to the appropriate range as specified in Low-Level IDCT Processing Elements by the host prior to passing the coefficient value to the accelerator for IDCT operation. MPEG-2 mismatch control, if necessary, is also the responsibility of the host, not the accelerator. (This might require the creation of extra "phantom" nonzero coefficients.)

Remarks

The DXVA_TCoefSingle structure is used whenever the HostResidDiff flag (bit 10 in the wMBtype member of the DXVA_MBctrl_P_OffHostIDCT_1 or DXVA_MBctrl_I_OffHostIDCT_1 structure) is 1 and the bConfig4GroupedCoefs member of the DXVA_ConfigPictureDecode structure is zero.

Requirements

Requirement	Value
Header	dxva.h (include Dxva.h)

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