- /** Offset to the next free data block. The mv_blocks hold a number
- pointing to the data blocks.
- - application - zeroes it on get_buffer() and after successful
- ff_draw_horiz_band().
- - libavcodec - each macroblock increases it with the number
- of coded blocks in it.
+ /** Number of the next free data block; one data block consists of
+ 64 short values in the data_blocks array.
+ All blocks before this one have already been claimed by placing their
+ position into the corresponding block description structure field,
+ that are part of the mv_blocks array.
+ - application - zeroes it on get_buffer().
+ A successful ff_draw_horiz_band() may zero it together
+ with start_mb_blocks_num.
+ - libavcodec - each decoded macroblock increases it by the number
+ of coded blocks it contains.