[MPlayer-users] Re: [-] Re: [-] Crop before deinterlacing OK?

[Rich Felker]

On Fri, Jul 08, 2005 at 09:44:38AM +0200, Matthias Wieser wrote:
> > > > Those of us using NTSC need to inverse telecine first
> > >
> > > I thought you only need to inverse teleine when capturing NTSC
> > > movies. Normal NTSC TV broadcasts can be deinterlaced with
> > > pp=[md|lb...], right?
> >
> > It depends on the content. You have to painstakingly check every
> > single thing you encode.
> 
> If I do not want to do this, it should have no disadvantage to always use 
> "pullup" (maybe except some higher CPU usage)?

No. pullup will give completely random/broken output on true
interlaced material. It will look very bad and choppy, and still be
combed. On the other hand, filmdint will deinterlace in these cases,
but the results will have ugly flicker.

The problem is very fundamental: different sources of video are
completely different formats, and the only way to get a smooth,
non-stuttering, non-aliased, non-flickering encode is to restore them
to the original format, rather than the "formatted for analog crt
television" format, which of course requires _knowing_ the original
format.

If you don't want to do this, the only way to make a decent-looking
encode is to duplicate what the television does: -vf
softpulldown,tfields=4. I think you'll need -ofps 60000/1001 and -fps
60000/1001 to get correct a/v sync, and perhaps -mc 0 and/or -noskip.
This will flicker/alias like an ordinary television set does, but at
least you'll have the full temporal smoothness and it works (albeit
nowhere near as pretty as inverse telecine) even for telecined
content. (BTW, using high-power temporal denoise3d at the end of the
chain can improve quality a good bit if you do this..).

> 
> > > >, and those
> > > > filters (eg. pullup) really do need to come before croping (or
> > > > anything else).
> > >
> > > Mplayer HTML documentation says: "[...]you must crop vertically by
> > > multiples of four or else the inverse-telecine filter will not have
> > > proper data." Which informations included in the TV signal are lost
> > > when cropping? I think DVD has something like a soft-telecine flag
> > > but TV?
> >
> > No, the problem is that the chroma will no longer correspond to the
> > right field. If you don't understand it, just accept it. YOU MUST USE
> > MULTIPLES OF 4 WHEN CROPPING INTERLACED (any field-based) CONTENT!
> 
> I do understand the multiples of four thing very well. That's why I wrote 
> in my initial email that I use a vertical offset which is a multiple of 
> four. What made me wonder is that RC wrote "those filters (eg. pullup) 
> really do need to come before croping (or anything else)."

If the source is mixed hard/soft telecine, pullup needs to see the
soft telecine flags on the frames. MPlayer's filter layer sucks and
most filters strip this information (actually fail to copy it), so
pullup (and similarly filmdint) need to be first if you want them to
use it.

> So: Is it ok to crop (multiple of four) before pullup or do I *have* to 
> use pullup before crop? That's my question.

Pure hard telecine: either is ok.
Mixed hard/soft: cannot crop first (unless you fix the crop filter to
preserve the flags. :)

BTW pullup has options you can pass to it to tell it to ignore junk at
the sides of the frames. This will speed it up a bit and improve
telecine matching, so it might be what you're looking for. And...
filmdint has builtin crop functionality for this very purpose, if you
want to use it instead!

Rich