[MPlayer-users] rescaling NTSC video streams

[Florin Andrei]

On Sun, 2003-03-02 at 20:04, D Richard Felker III wrote:
> On Sun, Mar 02, 2003 at 01:46:45PM -0800, Florin Andrei wrote:
> > 
> > (using mplayer-0.90rc4)
> > VIDEO:  [dvsd]  720x480  24bpp  29.97 fps  28771.8 kbps (3512.2 kbyte/s)
> > I'm playing them with mplayer, using -aspect 4:3.
> > mplayer performs the rescale by bumping up the vertical size from 480 to
> > 540:
> > I feel that it is somewhat unnatural to rescale NTSC streams this way. I
> > believe NTSC DV should be rescaled to 640x480. Here's why:
> > 1. NTSC DV has a frame size of 720x480 with non-square pixels which
> > coresponds to a real image of 640x480; that is, the _information_
> > contained in the 720x frame is really only 640x.
> 
> No. 640 is just the number that makes pixels square. [...] it's a
> continuous signal which you can sample at whatever rate you want. Only
> vertical resolution has an actual discrete number.

Pardon me? 720 _pixels_ = "continuous signal"? :-)

It may be continuous if you capture it with analog cameras (ancient
fully analog cameras, with a cathodic-ray tube and all that), but even
then, once you digitize it, you can kiss analogous bye-bye. And mplayer
doesn't plug into an analog feed :-) but it operates on digital video
streams.
And if you use CCDs (and all modern cameras use that kind of stuff)
there's no continuousness anywhere near, to begin with.

Anyways... we seem to agree that the vertical resolution is slightly
more important, and that was actually the essence of my suggestion:
don't mess with it when you can avoid it. Change the horizontal
resolution instead.

> Normally only the hardware scaler will be doing any auto-scaling.

Well, it depends on the hardware/software, doesn't it? :-)
The -aspect switch seems to play the same role in mplayer as some manual
settings in hardware decoders (force the aspect when you know it better
than the player), and that's why i made the suggestion.

> Apparently you're using -zoom or something.

No. If you re-read my message more carefully this time, you'll notice i
use -aspect. I was only talking about -aspect all the time.

> Why not just use -vop
> scale=640:480 instead? Or use -vop scale=-2:480 so everything gets
> scaled to ???x480 automatically based on aspect.

Yes, that should work. But, again, i was talking about the behaviour of
the -aspect switch.

> Or better yet, why not avoid scaling altogether and just set the video
> mode to 720x480?!?

Provided that the hardware supports it.
But yes, it's a good idea.

> > This is why i suggest to modify the -rescale parameter so that
> 
> Since when is there a -rescale parameter?

Brain typo.

-- 
Florin Andrei

http://florin.myip.org/