> Thread 0 encodes row 0 (mb 0-21). > When thead 0 finishes mb 1, start thread 1 encoding row 1 (mb 22-43), > making sure that it stays >= 2 mbs behind all the way. > When thread 0 finishes row 0, start it on row 2 (mb 44-65). > When thread 1 finished row 1 or thread 0 finishes mb 45 (whichever is > later), thread 1 starts row 3.