[MPlayer-users] Resizing video frame with mplayer for SVCD

[D Richard Felker III]

On Mon, Jan 19, 2004 at 11:07:40PM -0200, romildo at uber.com.br wrote:
> On Sat, Jan 17, 2004 at 08:26:54PM -0500, Matthew W. Miller wrote:
> > On Sat, Jan 17, 2004 at 09:58:07AM -0200, romildo at uber.com.br wrote:
> > >I want to know how to properly resize a movie for SVCD with mplayer. I
> > >have tried the expand and scale filters, but I did not get the expected
> > >result. The movie is an AVI with frame size 800x344.
> > 
> > Your logic sounds correct (expand to an appropriate 4:3 aspect ratio, 
> > then resize to 480x480), but you need to use a single -vf option with 
> > filters in order from first to last separated by commas.  Like this:
> > 
> > $ mencoder <others...> -vf expand=800:600,scale=480:480 <others...>
> > 
> > Personally, my preference is to use 0 chroma-skip and 0 sharpness 
> > parameter with scaler 2 (bicubic), so
> > 
> > $ mencoder <others...> -vf expand=800:600,scale=480:480:0:0 -sws 2 <others...>
> 
> I have another doubt. What would produce better quality:
> 
> 1) Expand first to bring the frame size to an aspect ratio 4:3
>    and then resize to 480x480. In this case the top and bottom
>    black borders will be added before scaling. Thus scaling
>    will work with that borders also.
> 
> 2) Scaling first to 480xH, and then expanding to bring the
>    frame size to 480x480. In this case scaling will be done
>    on the original video image, without any added black
>    borders.
> 
> Should I expect 2) to give better results than 1) ?

I expect 2 will be better as long as you align the black borders on
multiple-of-16 (macroblock) boundaries and 1 will probably be better
if you don't (because the smoothing from the scale filter will reduce
the severity of the sharp discontinuity the DCT has to deal with). But
there are lots of factors that go into 1, so I would stick with 2 and
always try to align the borders if possible.

Rich