Macroblock
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Macroblock is a term used in video compression, which represents a block of 16 by 16 pixels. Each macroblock contains 4 Y block, 1 Cb block, 1 Cr block (4:2:0). (It also could be represented by 4:2:2 or 4:4:4 YCbCr format). Macroblocks can be subdivided further into smaller blocks, called partitions. H.264, for example, supports block sizes as small as 4x4.
[edit] Macroblock coding
+------+------+-------+--------+-----+----+----+--------+
| ADDR | TYPE | QUANT | VECTOR | CBP | b0 | b1 | ... B5 |
+------+------+-------+--------+-----+----+----+--------+
* ADDR .... address of block in image
* TYPE .... identifies type of macroblock (intra-frame, inter frame, bi-directional inter frame)
* QUANT ... quantization value to vary quantization
* VECTOR... motion vector
* CBP...... Coded Block Pattern, some blocks in macroblock match well, some match poorly - this is bit mask indicating which one is present.
* the blocks (4 Y, 1 Cr, 1 Cb)
[edit] Macroblocking
This is a non-technical term used when macroblocks are missing and show up as video errors. Square areas of the picture do not show the correct portion of the image, but instead show a single color block. Advanced decoders hide these types of errors with a technique called error concealment. This effect is also referred to as microblocking.
