Understanding VC-1 - Revision history

Hopper: /* vc1DECBLK_UnpackIntraBlock */

2007-12-10T03:11:32Z

vc1DECBLK_UnpackIntraBlock

← Older revision		Revision as of 20:11, 9 December 2007
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	== vc1DECBLK_UnpackIntraBlock ==		== vc1DECBLK_UnpackIntraBlock ==
			This function decodes an intra-coded block in a macroblock.

	* zero out the 64-element coefficient array		* zero out the 64-element coefficient array
	* if (overlap filter ~~is enabled for this macroblock~~) or (~~this~~ is not an intra-coded ~~frame~~) or (profile is advanced)		* if (macroblock enables overlap filter) or (frame is not intra-coded) or (profile is advanced)
	** ~~call~~ [[Understanding VC-1#vc1PREDDCAC_DCDefault\|vc1PREDDCAC_DCDefault]] with a ~~parameter~~ of 128		** [[Understanding VC-1#vc1PREDDCAC_DCDefault\|vc1PREDDCAC_DCDefault]] with a bias of 128
	* else		* else
	** ~~call~~ [[Understanding VC-1#vc1PREDDCAC_DCDefault\|vc1PREDDCAC_DCDefault]] with a ~~parameter~~ of 0		** [[Understanding VC-1#vc1PREDDCAC_DCDefault\|vc1PREDDCAC_DCDefault]] with a bias of 0
	* block_type = [[Understanding VC-1#vc1PREDDCAC_PredictDCAC\|vc1PREDDCAC_PredictDCAC]]		* block_type = [[Understanding VC-1#vc1PREDDCAC_PredictDCAC\|vc1PREDDCAC_PredictDCAC]] in pred[] array
	* ~~save~~ block ~~type (associate with the current block)~~		* set block's block_type = block_type
	* [[Understanding VC-1#vc1DECBLK_UnpackDCDifferential\|vc1DECBLK_UnpackDCDifferential]]		* [[Understanding VC-1#vc1DECBLK_UnpackDCDifferential\|vc1DECBLK_UnpackDCDifferential]] in dc_differential
	* if ~~the current~~ block is marked as coded		* if block is marked as coded
	** NZC = 1		** set block's NZC = 1
	** ~~unpack AC coeffs into a temporary 64-element array with~~ [[Understanding VC-1#vc1DEC3DH_DecodeACRunLevel\|vc1DEC3DH_DecodeACRunLevel]]		** [[Understanding VC-1#vc1DEC3DH_DecodeACRunLevel\|vc1DEC3DH_DecodeACRunLevel]]
	** [[Understanding VC-1#vc1DECZZ_DeZigZagBlock\|vc1DECZZ_DeZigZagBlock]]		** [[Understanding VC-1#vc1DECZZ_DeZigZagBlock\|vc1DECZZ_DeZigZagBlock]]
	* else		* else
	** ~~no AC coefficients in this~~ block (NZC = 0)		** set block's NZC = 0
	* if ~~AC prediction~~ is enabled ~~for this MB~~		* if macroblock's ACPRED is enabled
	** [[Understanding VC-1#vc1DECBLK_ApplyACPrediction\|vc1DECBLK_ApplyACPrediction]]		** [[Understanding VC-1#vc1DECBLK_ApplyACPrediction\|vc1DECBLK_ApplyACPrediction]]
	* ~~compute quantized~~ DC coefficient		* set DC coefficient coeff[0] = pred[0] + dc_differential
	* [[Understanding VC-1#vc1PREDDCAC_CopyDCAC\|vc1PREDDCAC_CopyDCAC]]		* [[Understanding VC-1#vc1PREDDCAC_CopyDCAC\|vc1PREDDCAC_CopyDCAC]]

Hopper: /* vc1DECBLK_DecodeBlockLayer */

2007-12-10T02:57:49Z

vc1DECBLK_DecodeBlockLayer

← Older revision		Revision as of 19:57, 9 December 2007
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	== vc1DECBLK_DecodeBlockLayer ==		== vc1DECBLK_DecodeBlockLayer ==
	This function unpacks and reconstructs a macroblock.		This function unpacks and reconstructs a macroblock. The macroblock is read from the current position in the bitstream. VC-1 only allows YUV 4:2:0 so there are always 6 blocks in a macroblock.

	* foreach block (Y0, Y1, Y2, Y3, U, V) in a macroblock		* foreach block (Y0, Y1, Y2, Y3, U(Cr), V(Cb)) in a macroblock
	** if the ~~current~~ macroblock is not skipped		** if the macroblock is not skipped
	*** if the block is intra-coded		*** if the block is intra-coded
	**** [[Understanding VC-1#vc1DECBLK_UnpackIntraBlock\|vc1DECBLK_UnpackIntraBlock]]		**** [[Understanding VC-1#vc1DECBLK_UnpackIntraBlock\|vc1DECBLK_UnpackIntraBlock]]

Hopper: /* vc1ITRANS_InverseTransform_AnnexA1 */

2007-12-05T00:20:28Z

vc1ITRANS_InverseTransform_AnnexA1

← Older revision		Revision as of 17:20, 4 December 2007
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	VC-1 block sizes are 4x4, 4x8, 8x4, and 8x8. The transform takes 4 parameters: input[64], output[64], width, and height. For the transform matrices and constants, see [[VC-1 Tables#Transform Tables\|VC-1 Tables-- Transform Tables]]		VC-1 block sizes are 4x4, 4x8, 8x4, and 8x8. The transform takes 4 parameters: input[64], output[64], width, and height. For the transform matrices and constants, see [[VC-1 Tables#Transform Tables\|VC-1 Tables-- Transform Tables]]

			''note: The SRD comments ''Equation: E = (M * T + 4) >> 3'' in this function. This is incorrect. The correct equation is ''E = (D * T + 4) >> 3'' as so it is defined and implemented.''

	* declare temp_matrix[64]		* declare temp_matrix[64]

Hopper: /* vc1DECBLK_ApplyACPrediction */

2007-12-04T21:36:11Z

vc1DECBLK_ApplyACPrediction

← Older revision		Revision as of 14:36, 4 December 2007
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	This function takes an 8x8 block of transform coefficients, an array of 7 AC coefficient predictors and a flag indicating the block type.		This function takes an 8x8 block of transform coefficients, an array of 7 AC coefficient predictors and a flag indicating the block type.

	* if ~~then~~ block type if INTRA_TOP		* if the block type is INTRA_TOP
	** add 7 AC coefficients to the 7 top row coefficients of the 8x8 block without the first (left-top corner)		** add 7 AC coefficients to the 7 top row coefficients of the 8x8 block without the first (left-top corner)
	* if ~~then~~ block type if INTRA_LEFT		* if the block type is INTRA_LEFT
	** add 7 AC coefficients to the 7 left column coefficients of the 8x8 block without the first (left-top corner)		** add 7 AC coefficients to the 7 left column coefficients of the 8x8 block without the first (left-top corner)

Hopper: /* vc1DECBITPL_DecodeNorm2Bits */

2007-12-04T15:55:14Z

vc1DECBITPL_DecodeNorm2Bits

← Older revision		Revision as of 08:55, 4 December 2007
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	* foreach i in MBcount/2		* foreach i in MBcount/2
	** decode a VLC from the bitstream using the Norm-2 [[(VC-1 Tables\|VLC table]]		** decode a VLC from the bitstream using the Norm-2 [[(VC-1 Tables\|VLC table]]
	** the decoded VLC contains values for the next 2 MBs, 1 bit each starting with the msb
	** if the invert flag is set		** if the invert flag is set
	*** invert the value		*** invert the decoded value
			** the 2-bit value is laid out as a 'ab' bit sequence (msb first) and applied to the next 2 MBs

			''note that the bits are applied differently to Norm-6. Norm-2 uses msb first but Norm-6 uses lsb first.

	== vc1DECBITPL_DecodeNorm6Bits ==		== vc1DECBITPL_DecodeNorm6Bits ==

Hopper: /* vc1DECBITPL_DecodeNorm6Bits */

2007-12-04T15:47:44Z

vc1DECBITPL_DecodeNorm6Bits

← Older revision		Revision as of 08:47, 4 December 2007
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	== vc1DECBITPL_DecodeNorm6Bits ==		== vc1DECBITPL_DecodeNorm6Bits ==
	This function takes a bitplane data structure, an invert bit, and the width and height of the frame in macroblocks. It decodes 1 bit per MB~~. The bitplane data structure is assumed to be arranged as a macroblock frame with (width x height) macroblocks~~.		This function takes a bitplane data structure, an invert bit, and the width (MBwidth) and height (MBheight) of the frame in macroblocks. It decodes 1 bit per MB.
	* if the MBheight is divisible by 3 but the MBwidth is not		* if the MBheight is divisible by 3 but the MBwidth is not
	** decode using 2x3 tiles		** decode using 2x3 tiles as follows...
	** ~~compute ResidualX as MBwidth & 1~~		**: a b
	** ~~set ResidualY 0~~		**: c d
	** foreach 2x3 tile in bitplane data structure progressing from left -> right, top -> bottom		**: e f
	*** [[VC-1 Tables\|VLC]]~~: 6-bit~~ decoded value		** foreach 2x3 tile in bitplane data structure progressing from left → right and top → bottom
	*** the ~~decoded~~ 6-bit value is laid out as '~~abcdef~~' ~~which corresponds to~~ the ~~following~~ arrangement ~~in the bitplane:~~		*** decode a VLC from the bitstream using the Norm-6 [[VC-1 Tables\|VLC table]]
	~~f e~~		*** if the invert flag is set
	~~d c~~		**** invert the decoded value
	~~b a~~		*** the 6-bit value is laid out as a 'fedcba' bit sequence (lsb first) and applied in the arrangement given above
	*** apply invert flag as necessary		** ResidualX = MBwidth modulo 2
			** ResidualY = MBheight modulo 3 ''which is always 0''
	* else		* else
	** decode using 3x2 tiles		** decode using 3x2 tiles as follows...
	** ~~compute ResidualX as MBwidth % 3~~		**: a b c
	** ~~compute ResidualY as MBwidth & 1~~		**: d e f
	** foreach 3x2 tile in bitplane data structure progressing from left -> right, top -> bottom		** foreach 3x2 tile in bitplane data structure progressing from left → right and top → bottom
	*** [[VC-1 Tables\|VLC]]~~: 6-bit~~ decoded value		*** decode a VLC from the bitstream using the Norm-6 [[VC-1 Tables\|VLC table]]
	*** the ~~decoded~~ 6-bit value is laid out as '~~abcdef~~' ~~which corresponds to~~ the ~~following~~ arrangement ~~in the bitplane:~~		*** if the invert flag is set
	~~f e d~~		**** invert the decoded value
	~~c b a~~		*** the 6-bit value is laid out as a 'fedcba' bit sequence (lsb first) and applied in the arrangement given above
	*** ~~apply invert flag~~ as ~~necessary~~		** ResidualX = MBwidth modulo 3
	* ~~decode residual bits of frame edges using colskip and~~ rowskip ~~algorithms~~		** ResidualY = MBheight modulo 2
	~~'''(UNFINISHED)'''~~		* foreach i in ResidualX
			** read the column as defined in colskip
			* foreach i in ResidualY
			** read the row as defined in rowskip

	== vc1DECBITPL_DecodeRawBits ==		== vc1DECBITPL_DecodeRawBits ==

Hopper: /* vc1DECBITPL_DecodeNorm2Bits */

2007-12-04T15:13:57Z

vc1DECBITPL_DecodeNorm2Bits

← Older revision		Revision as of 08:13, 4 December 2007
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	== vc1DECBITPL_DecodeNorm2Bits ==		== vc1DECBITPL_DecodeNorm2Bits ==
	This function takes a bitplane data structure, an invert bit, and the width and height of the frame in macroblocks. It decodes 1 bit per MB.		This function takes a bitplane data structure, an invert bit, and the width (MBwidth) and height (MBheight) of the frame in macroblocks. It decodes 1 bit per MB.
	* MBcount = MBwidth * MBheight		* MBcount = count of MBs in frame (MBwidth * MBheight)
	* if MBcount is odd		* if MBcount is odd
	** 1 bit: first ~~bitplane~~ flag		** 1 bit: value defines the first MB
	** ~~apply~~ invert ~~flag as necessary~~		** if the invert flag is set
	** ~~count--~~		*** invert the value
	* foreach i in ~~count~~/2		** decrement MBcount
	** [[VC-1 Tables\|VLC]]~~: Norm-2 table VLC~~		* foreach i in MBcount/2
	** the decoded VLC contains the next 2 ~~bits~~, ~~xy: x represents~~ the ~~1st of~~ the ~~2 bits and y~~ is ~~the second~~		** decode a VLC from the bitstream using the Norm-2 [[(VC-1 Tables\|VLC table]]
	** ~~apply~~ invert ~~flag as necessary~~		** the decoded VLC contains values for the next 2 MBs, 1 bit each starting with the msb
			** if the invert flag is set
			*** invert the value

	== vc1DECBITPL_DecodeNorm6Bits ==		== vc1DECBITPL_DecodeNorm6Bits ==

Hopper: /* vc1DECBLK_ApplyACPrediction */

2007-12-03T21:28:16Z

vc1DECBLK_ApplyACPrediction

← Older revision		Revision as of 14:28, 3 December 2007
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	== vc1DECBLK_ApplyACPrediction ==		== vc1DECBLK_ApplyACPrediction ==
	This function takes an 8x8 block of transform coefficients, an array of 7 AC coefficient predictors and a flag indicating ~~whether~~ the ~~predictors should be applied along~~ the ~~left column or~~ top row of AC coefficients of the block.		This function takes an 8x8 block of transform coefficients, an array of 7 AC coefficient predictors and a flag indicating the block type.

			* if then block type if INTRA_TOP
			** add 7 AC coefficients to the 7 top row coefficients of the 8x8 block without the first (left-top corner)
			* if then block type if INTRA_LEFT
			** add 7 AC coefficients to the 7 left column coefficients of the 8x8 block without the first (left-top corner)

	== vc1DECBLK_DecodeBlockLayer ==		== vc1DECBLK_DecodeBlockLayer ==

Hopper: /* vc1DECBLK_UnpackDCDifferential */

2007-12-03T21:22:05Z

vc1DECBLK_UnpackDCDifferential

← Older revision		Revision as of 14:22, 3 December 2007
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	== vc1DECBLK_UnpackDCDifferential ==		== vc1DECBLK_UnpackDCDifferential ==
	This function unpacks from the encoded bitstream the DC transform coefficient differential value for an intra-coded block ~~using the following algorithm:~~		This function unpacks from the encoded bitstream the DC transform coefficient differential value for an intra-coded block.
	* select one of 4 VLC tables ~~based on whether the block is a Y block or a C block and whether the picture parameters data structure specifies low motion or high motion~~ (see [[VC-1 Tables#DC Differential VLC Tables\|VC-1 Tables]])		* select one of 4 VLC tables (see [[VC-1 Tables#DC Differential VLC Tables\|VC-1 Tables]]) based on
	* decode VLC from bitstream ~~as DC differential~~		** block is a Y or C block
			** picture parameters specify intra transform DC (high/low motion)
			* decode DC differential as a VLC from the bitstream using that table
	* if the DC differential is not 0		* if the DC differential is not 0
	** if the DC differential value is ~~actually an~~ escape code ~~(the SRD used -2 to indicated this)~~		** if the DC differential value is the escape code
	*** ~~decide how many bits to retrieve from the bistream based on~~ the current ~~MB position's~~ quantizer ~~structure's Quant value:~~		*** if the current macroblock quantizer is
	**** ~~if the value is~~ 1~~, the~~ DC differential ~~is the~~ next 10 bits		**** 1: DC differential = next 10 bits in bitstream
	**** ~~else if the value is~~ 2~~, the~~ DC differential ~~is the~~ next 9 bits		**** 2: DC differential = next 9 bits in bitstream
	**** else ~~the~~ DC differential ~~is the~~ next 8 bits		**** else DC differential = next 8 bits in bitstream
	** else		** else
	*** if the current ~~MB position's~~ quantizer ~~structure's Quant value~~ is		*** if the current macroblock quantizer is
	**** 1: value = next 2 bits in bitstream; DC differential ~~value~~ = ~~dcdiff~~ * 4 + value - 3		**** 1: value = next 2 bits in bitstream; DC differential = DC differential * 4 + value - 3
	**** 2: value = next bit in bitstream; DC differential ~~value~~ = ~~dcdiff~~ * 2 + value - 1		**** 2: value = next bit in bitstream; DC differential = DC differential * 2 + value - 1
	** the ~~next~~ bit ~~in the bitstream~~ is the ~~sign bit; a 1 bit indicates a negative~~ DC differential ~~value~~		** 1 bit: sign
			** if the sign bit is set
			*** negate the DC differential

	== vc1DECBLK_UnpackInterBlock ==		== vc1DECBLK_UnpackInterBlock ==

Hopper: /* vc1DEC3DH_DecodeACRunLevel */

2007-12-03T21:05:31Z

vc1DEC3DH_DecodeACRunLevel

← Older revision		Revision as of 14:05, 3 December 2007
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	** advance to the next block in the coefficient buffer		** advance to the next block in the coefficient buffer

	''Note that there is no check if run is larger than the maximum number of coefficients per subblock. It is ~~unclean~~ what the specification states in such case.''		''Note that there is no check if run is larger than the maximum number of coefficients per subblock. It is unclear what the specification states in such case.''

	== vc1DEC3DH_UnpackTransformACCoef ==		== vc1DEC3DH_UnpackTransformACCoef ==