In H.261, the first video codec to use macroblocks, transform blocks have a fixed size of 8×8 samples.
In more modern macroblock-based video coding standards such as H.263 and H.264/AVC, transform blocks can be of sizes other than 8×8 samples.
[1][2] In more modern standards such as H.264/AVC, a macroblock can be split into multiple variable-sized prediction blocks, called partitions.
[4] In H.264/AVC, prediction partition size ranges from 4×4 to 16×16 samples for both inter-prediction (motion compensation) and intra-prediction.
[4] A possible bitstream representation of a macroblock in a video codec which uses motion compensation and transform coding is given below.