Flexible Macroblock Ordering or FMO is one of several error resilience tools defined in the Baseline profile of the H.264/MPEG-4 AVC video compression standard.
Nearly all video codecs allow Region of Interest coding, in which specific macroblocks are targeted to receive more or less quality, the canonical example being a newscaster's head being given a higher ratio of bits than the background.
[3] With these patterns, FMO allows one retain a better localized visual context so that error-concealment algorithms can reconstruct missing content.
Rather than create a slice in order to periodically refresh entirely with I or IDR frames, I-blocks can be sent in any desired pattern while predicted blocks make up the rest of the picture.
Although errors will still propagate horizontally, I-blocks can be sent in patterns, such as favoring a region of interest or a scattered checkerboard, to simulate shaped slice refreshes.
The much more common Constrained Baseline, Main, and all High profiles do not support it, and software that can create or decode it is rare.