Enable some optional macroblocktypes (default:p8x8,b8x8,i8x8,i4x4).
p8x8 Enable types p16x8, p8x16, p8x8.
p4x4 Enable types p8x4, p4x8, p4x4. p4x4 is recommended only
with subq >= 5, and only at low resolutions.
b8x8 Enable types b16x8, b8x16, b8x8.
i8x8 Enable type i8x8. i8x8 has no effect unless 8x8dct is enabled.
i4x4 Enable type i4x4.
all Enable all of the above types.
none Disable all of the above types.
Regardless of this option, macroblock types p16x16, b16x16, and
i16x16 are always enabled.
The idea is to find the type and size that best describe a cer-
tain area of the picture. For example, a global pan is better
represented by 16x16 blocks, while small moving objects are bet-
ter represented by smaller blocks.
