Add support for mpeg2dec's 4:2:2 and 4:4:4 formats. This hasn't been tested
yet (4:2:2 is a HP feature not implemented yet in mpeg2enc). Traditional 4:2:0 has been tested and works the same as it always has.
Authored by: sms00 2004-05-07
Parent: [r2349]
Child: [r2351]
