[MPlayer-dev-eng] New inverse-telecine filter

[Zoltan Hidvegi]

> > So if there are two algorithms for upsampling, there must be two
> > algorithms for downsampling as well, the problem is there are no flags
> > in broadcast TV to tell you which one to use.
> 
>   Of course not, because you don't need to.  Broadcast TV is sent as
> 4:2:2.  The bttv driver converts this from 4:2:2 to 4:2:0, currently by
> dropping every second line of chroma.  This happens to be reasonable
> (but poor quality - should be filtered!)  if the field happens to be
> from a progressive frame.  But since it might not be, the bttv driver
> should use a standard for interlaced chroma, basically, every second
> scanline of chroma should be from the next field (again poor, but better
> for interlaced content).

With interlaced downsampling the color samples will come from lines 0,
1, 4, 5, 8, 9, ..., i.e., keep two lines, drop two lines.  If you do
that on a progressive frame, it will look bad, since every second
chroma line would be 1 luma pixel higher than normal, so you would
have to interpolate them back to the right place.  Probably you end up
losing 2/3 of the vertical chroma resolution instead of only losing
half if you did progressive downscale to begin with.

Zoli