[MPlayer-users] rescaling NTSC video streams

D Richard Felker III dalias at aerifal.cx
Mon Mar 3 06:40:43 CET 2003

On Sun, Mar 02, 2003 at 08:47:30PM -0800, Florin Andrei wrote:
> [Automatic answer: RTFM (read DOCS, FAQ), also read DOCS/bugreports.html]
> 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"? :-)

No, the original signal is continuous, before sampling. So it's
nonsense to call 640 the "real" resolution. You said "the
_information_ contained in the 720x frame is really only 640x", and
this is blatently false.

> 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.

I agree that the default behavior is annoying, especially with
interlaced material. However, some hardware CANNOT scale down, so the
only reasonable/working default is to scale up vertical... :(

> > 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.

No, your output showed that you were using software scaler. -aspect
will not enable this by itself.

> > 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.

The -aspect option doesn't do anything in itself but override the
aspect from the file headers.

> > 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.

AFAIK all hardware supports it. If not then it's very broken hardware...


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