[MPlayer-users] Re: AVI->DVD: Problem understanding expand and scale

[Rich Felker]

On Mon, Oct 10, 2005 at 10:38:53AM -0400, Giacomo Comes wrote:
> On Sun, Oct 09, 2005 at 10:16:53AM -0400, Rich Felker wrote:
> > On Sat, Oct 08, 2005 at 02:12:22PM -0400, Giacomo Comes wrote:
> > > On Sat, Oct 08, 2005 at 09:15:11AM +0200, Thomas Heuving wrote:
> > > > Nico Sabbi schrieb am Thu, 06 Oct 2005 10:10:04 +0200:
> > > > >>  mencoder -oac lavc -ovc lavc -of mpeg -mpegopts format=dvd -vf
> > > > >>  expand=672:378:16:4,dsize=16/9,scale=720:576,harddup
> > > > >>  -lavcopts aspect=16/9:acodec=ac3:abitrate=192:vcodec=mpeg2video:
> > > > >>  vrc_buf_size=1835:vrc_maxrate=9800:vbitrate=5000:keyint=18
> > > > >>  -o test.mpg -endpos 100 my.avi
> > > > >
> > > > > why not simply -vf scale=-1:-10,expand=720:576,harddup
> > > > > to keep the original width, or
> > > > 
> > > > that works, but I want some black borders as most DVD-Players seem
> > > > to cut some of the original content in order to present the material
> > > > on the Television. I think that's the reason why commercial content
> > > > tends to have black borders too (?).
> > > > Less complicated is
> > > > scale=-1:10:::::pal (or ntsc)
> > > > so you don't have to expand by yourself.
> > > > 
> > > > > -vf scale 720:-10,expand=720:576,harddup  to resize the width to 720
> > > > > and the height according to the A/R ?
> > > > 
> > > > This gives bad distortions.
> > > > 
> > > > > unnecessarily complicated
> > > > 
> > > > But it seems to be necessary to do two invokations, as I didn't find
> > > >  and nobody mentioned a working example of putting black borders and do
> > > >  a scaling in one go.
> > > 
> > > I already told you that that if you do scale-expand you can do it in one pass.
> > > 
> > > For you particular movie
> > > 
> > > -vf scale=684:547,expand=720:576  will add 5% border and
> > 
> > Scaling to odd height is _always_ invalid for 4:2:0 pictures. MPlayer
> > will do it anyway but it will make bad chroma artifacts at the edge.
> > Ideally you should line the borders up to mod-16 boundaries if you're
> > going to add borders, anyway.
> 
> Noted.
> By the way, if you want add a border probably it is because you intend to
> watch the movie on a TV. And many TV do not show a correct
> picture close to the borders. 
> The chroma artifacts usually go unnoticed.

Well it certainly matters for letterbox movies. In any case it's just
plain wrong, don't do it. The mod-16 thing is important too even if
you can't see the borders because it will waste bits and reduce
overall quality.

Rich