1) This is a bug:
The V101 specification defines the legal CDCI horizontal
chrominance subsampling values as 1, 2, and 4.
only accepts the values 1 and 2.
2) This is just a comment:
The horizontal and vertical chroma subsampling values
map to the following: 4:4:4 (V=1 H=1), 4:2:2 (V=1 H=2),
4:1:1 (V=1 H=4), and 4:2:0 (V=2 H=2).
To the best of my knowledge, the following V/H pairs are
not in common use: V=2 H=1, and V=2 H=4.
Since the individual H/V values are enforced, perhaps
that should also be enforced? It may be troublesome to
do so, however, since the values are set independently