[MPlayer-dev-eng] swScaler interlaced support?

[D Richard Felker III]

Hey Michael (or anyone else interested),

I've been thinking about some issues with interlaced video and
scaling. In particular, this comes out of the fact that bttv has a
huge bug, whereby you can only capture interlaced video properly in
yuy2/uyvu mode (if you pick yv12 the chroma is corrupted). Then, since
you're (of course) going to write it to yv12 (mpeg1/2/4), you have to
resample (with swScaler) to 4:2:0, while preserving the interlacing.
The only way to do this right now is with the horrible, slow command
line:

mencoder -tv outfmt=yuy2 -vf il=d:d,scale,format=yv12,il=i:i ...

This does lots of unnecessary copying just to keep from ruining the
interlacing of the chroma plane.

Would it be possible to adapt swScaler internally so that it can
handle interlaced video, or else improve the vf_scale wrapper so that
it optionally (if an interlacing option is set) operates on the two
fields independently (using stride arithmetic hacks)?

Rich