Utterly useless, but the intention is to make dealing with corner case
pixel formats (forced upon us by FFmpeg, very rarely) less of a pain.
The zimg wrapper will use them. (It already supports these formats
automatically, but it will help with its internals.)
Y1 is considered RGB, even though gray formats are generally treated as
YUV for various reasons. mpv will default all YUV formats to limited
range internally, which makes no sense for a 1 bit format, so this is a
problem. I wanted to avoid that mp_image_params_guess_csp() (which
applies the default) explicitly checks for an image format, so although
a bit janky, this seems to be a good solution, especially because I
really don't give a shit about these formats, other than having to
handle them. It's notable that AV_PIX_FMT_MONOBLACK (also 1 bit gray,
just packed) already explicitly marked itself as RGB.
Again worthless, slow, and only for libswscale parity.
With this, we support all formats libswscale supports, except bayer
input, and rgb4/bgr4 output. We even support some formats libswscale
doesn't.
It's possible that the zimg wrapper isn't always as fast as libswscale.
But there is optimization potential: the inner repack loops are
self-contained enough that they could be reasonably be implemented in
assembler (probably), and doing everything slice-wise should reduce the
overhead of the separate pack/unpack stages.
Just lazily tested.
The comment on AV_PIX_FMT_Y210LE seems to be wrong. It claims it's "like
YUYV422", bit it seems more like YVYU422, at last the way libswscale
input treats it. Maybe Intel pays its developers too much?
The repacker inner lop is probably rather inefficient. In theory we
could optimize it by reading the packed pixels as words, doing the
component reshuffling using compile time values etc., but I'd rather
keep the code size small. It's already bad enough that we have to
support 16 bit per component variants, just because this one Intel guy
couldn't keep it in his pants. In general, I can't be bothered to spend
time on optimizing it; I'm only doing this for fun (i.e. masochistic
obligation).
Generic statement about how this is not really appropriate, etc., and
only useful for temporary debugging things, and how I commit it anyway
despite violating my own principles (and how I'd reject this change if
it came from you).
wm4