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

Billy Biggs vektor at dumbterm.net
Thu Dec 4 23:01:44 CET 2003

Zoltan Hidvegi (mplayer at hzoli.2y.net):

> > Are you asking how to convert 4:2:2 to 4:2:0 ?  There are
> > specifications for this depending on what 4:2:0 standard you are
> > going to.  The MPEG2 spec has some details on the filter to use.
> Yes, but the MPEG standard actually has two algorithms you have to use
> depending on whether the content is progressive or interlaced.  And
> many (if not most) progressive DVD players do not do it right, which
> is known as the chroma bug.  See
> http://www.hometheaterhifi.com/volume_8_2/dvd-benchmark-special-report-chroma-bug-4-2001.html
> for a detailed discussion.  It mostly talks about upsampling for
> playback, but downsampling has the same problems.

  I'm aware of this problem (and that article is a great reference), but
my point is that the spec is not ambiguous, especially for downsampling.

  Why do you care about 4:2:2 to 4:2:0 anyway though?  Let's bring this
back to bttv and what it should do.  If you ask bttv for 4:2:0, it
should _always_ mean that we want interlaced chroma, since this is the
only intelligent choice.  Furthermore, using the definition of
interlaced chroma from MPEG2 is well defined, with how to go from 4:2:2.
This is the correct choice regardless and it works just fine for
progressive material: you deinterlace as normal, if you detect 2-2
pulldown (or 2-3 pulldown), you know how to convert these to get good
output.  You have not screwed yourself in any way.


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