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

[Rich Felker]

On Thu, Jul 07, 2005 at 10:34:40AM +0200, Matthias Wieser wrote:
> Am Donnerstag, 7. Juli 2005 03:08 schrieb RC:
> > On Wed, 6 Jul 2005 11:08:17 +0200
> >
> > Matthias Wieser <mwieser at gmx.de> wrote:
> > > Is there any disadvantage in doing crop before deinterlacing?
> >
> > Is there any advantage in doing crop before deinterlacing?
> 
> Less work for the deinterlacing filter.

Yep. It can be useful, however you must do it right..

> > As long as 
> > you stick to multiples of 4 you should be fine.
> 
> For normal PAL and NTSC broadcasts, but not for telecined NTSC movies, am 
> I right?

No. It must ALWAYS be a multiple of 4 if the input is field-based.
Whether the original source was progressive frames or video is
irrelevant.

> > 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.

> >, 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!

Rich