In this mode, all YUV4MPEG2 chroma types are accepted in input
(versus 4:4:4 only), and the output has all of the channels
tiled side-by-side in one grayscale image. No colorspace
conversion is performed --- the bytes are emitted just as
they were encountered in the input, merely rearranged.
This overall effect is akin to the "pgmpipe" format of mplayer.
Its intended use is for debugging streams, since it allows you
to inspect each raw channel in the Y'CbCr space using good old
R'G'B' graphics programs.
