DCT Block

The Y, U, V pixels in one frame shall be divided into DCT blocks. All DCT blocks for 625-50 system and DCT blocks except for rightmost DCT blocks in U and V for 525-60 system are structured with a rectangular area of eight vertical lines and eight horizontal pixels in a frame.

For 525-60 system, the rightmost DCT blocks in U and V are structured with 16 vertical lines and four horizontal pixels. The rightmost DCT block is reconstructed to eight vertical lines and eight horizontal pixels by moving the lower part of eight vertical lines and four horizontal pixels to the higher part of eight vertical lines and four horizontal pixels.

DCT Block Structure

Six DCT blocks Y0, Y1, Y2, Y3, U, V form a macroblock.

Macroblock Structure for 525-60 System (Except Rightmost Macroblock)

Macroblock Structure for 625-50 System and Rightmost Macroblock of 525-60 System

27 DCT macroblocks form a superblock. (Each cell stands for one macroblock).

DCT Superblock Structure for 525-60 System

System 525-60 has three types of superblocks.

DCT Superblock Structure for 625-50 System

All superblocks of 625-50 system are of the same type.

A video segment consists of five macroblocks, which are gathered from various areas as below:

Macroblock Absolute Coordinates

where k is within the interval [0,26], n = 10 for 525-60 system, n = 12 for 625-50 system, and j is the vertical order in the superblock.

Data in a video segment is compressed and transformed to the data of 385 bytes ( compressed segment). A compressed segment consists of five compressed macroblocks. Each compressed macroblock consists of 77 bytes.

Arrangement of Compressed Macroblock

Arrangement of Compressed Macroblock Header (H)

Arrangement of Y compressed blocks cbY0, cbY1, cbY2, cbY3

Arrangement Cr compressed blocks cbU, cbV

Type of block is equal to 1 when the difference between two fields is small (m0=0). Type of block is equal to 2 when the difference between two fields is big (m0=1).

Each DCT block is classified into four classes. For selecting quantization step, class number is used.

DV Functions
Function Short Name	Description
Decoding
Variable Length Decoding
InitAllocHuffmanTable_DV	Allocates memory and initializes the table that contains codes for DCT coefficients (Run-Level codes).
HuffmanDecodeSegment_DV	Decodes and rearranges a segment block, multiplies the first block element by 2.
HuffmanDecodeSegment_DV100	Decodes and rearranges a DV100 segment block, multiplies the first block element by 128.
HuffmanDecodeSegmentOnePass_DV	Performs the first pass of video segment decoding, rearranges the segment block, multiplies the first block element by 128.
FreeHuffmanTable_DV	Frees the memory allocated for VLC table.
Inverse Quantization
QuantInv_DV	Performs inverse quantization on a block.
QuantWeightBlockInv_DV	Performs inverse quantization and inverse weighting on a block.
QuantWeightBlockInv_DV100	Performs inverse quantization and inverse weighting on a block according to DV100 standard.
Inverse Discrete Cosine Transformation
DCT2x4x8Inv	Performs the inverse DCT for block of type 2 ( m0=1).
DCT8x4x2To4x4Inv_DV	Performs the inverse DCT for block 2x4x8 and then creates block 4x4.
Encoding
Discrete Cosine Transformation
DCT2x4x8Frw	Performs DCT for a block of type 2.
CountZeros8x8	Evaluates number of zeros in a block.
Color Conversion
YCrCb411ToYCbCr422_5MBDV, YCrCb411ToYCbCr422_ZoomOut2_5MBDV, YCrCb411ToYCbCr422_ZoomOut4_5MBDV, YCrCb411ToYCbCr422_ZoomOut8_5MBDV	Convert five macroblocks from YUV411 format into YUV2 format.
YCrCb411ToYCbCr422_16x4x5MB_DV, YCrCb411ToYCbCr422_8x8MB_DV	Convert five reduced YCrCb411 macroblocks into YCrCb422 reduced macroblocks.
YCrCb411ToYCbCr422_EdgeDV, YCrCb411ToYCbCr422_ZoomOut2_EdgeDV, YCrCb411ToYCbCr422_ZoomOut4_EdgeDV, YCrCb411ToYCbCr422_ZoomOut8_EdgeDV	Convert a YCrCb411 macroblock into a YCrCb422 macroblock at the right edge of destination image.
YCrCb420ToYCbCr422_5MBDV, YCrCb420ToYCbCr422_ZoomOut2_5MBDV, YCrCb420ToYCbCr422_ZoomOut4_5MBDV, YCrCb420ToYCbCr422_ZoomOut8_5MBDV	Convert five YCrCb420 macroblocks into YCrCb422 macroblocks.
YCrCb420ToYCbCr422_8x8x5MB_DV	Converts five reduced YCrCb420 macroblocks into YCrCb422 reduced macroblocks.
YCrCb422ToYCbCr422_5MBDV, YCrCb422ToYCbCr422_ZoomOut2_5MBDV, YCrCb422ToYCbCr422_ZoomOut4_5MBDV, YCrCb422ToYCbCr422_ZoomOut8_5MBDV	Convert five YCrCb422 macroblocks into YCbCr422 macroblocks.
YCrCb422ToYCbCr422_8x4x5MB_DV	Converts five reduced YCrCb422 macroblocks into YCrCb422 reduced macroblocks.
YCrCb422ToYCbCr422_10HalvesMB16x8_DV100	Converts ten YCrCb422 half-macroblocks into YCrCb422 half-macroblocks.