[MPlayer-users] Re: best encoder ?

[D Richard Felker III]

On Mon, Jul 22, 2002 at 11:30:36PM +0200, Martin Hoffmann wrote:
> > > + Correct Aspect Ratio sacling in case of 16:9 material (current is not
> > > exactly :-()
> >
> > Hopefully this will be a configurable option ? Since I crop my
> > "cinemascoped" movies an aspect ratio would be no good idea ;)
> Don't get me wrong, AVI alway has sqare pixels per definition - I'm not going 
> to break this for 16:9 material (for 4:3 i do, but that's another story) - I 
> had just some mistake when scaling 16:9 material !
> Now it does scale to the correct Y values: 720x405  or 480x270 and so on !
> Old versions did scale to 480x432 which in fact is NOT 16:9 assuming sqare 
> pixels !
> 
> Does this break anything you use ?
> If so, tell me how it should be ? Leave it 480x576 (original resolution) - or 
> what ?

If you're going to scale, you *must* deinterlace or you'll get
*horrible* artifacts. Unfortunately I've seen way too many movies
encoded this way -- please don't make the situation even worse. If
you'd like to see a sample movie or even just a screenshot from one,
let me know. Perhaps this can be fixed with a scaler that treats both
fields separately, but I've never heard of one of these, especially
not in mplayer, and I'm not sure the scaler would do a good job
keeping the image smooth with only every other line to work with.

Personally I would just recommend scaling down vertically by about
1/2, then there's no reason not to deinterlace since you're losing
half the lines anyway -- no additional "blurring" as you claim.

> > > So, cropping is heard to do automatically, since i have no way to analyze
> > > pictures :-( Rescaling could be added depending on wanted_size and length
> > > of
> >
> > You do have a way to analyse the pictures using something like
> >
> > mencoder -cropdetect -i mymovie.mpg -frames 500 -o yugga.avi
> >
> > but this is far away from being perfect since f.e. a TV stations logo
> > which appears in the black area lets "cropdetect" think, the movie
> > starts at that vertical position... But cropping by hand is *very*
> > effective resulting in a much smaller sized AVI :)
> Is the size gain really that much by cropping the bars ? I always thought this 
> would not be much gain ...

Yes, it's huge. The sharp border between solid black and the natural
image makes lots of coefficients that shouldn't be there blow up huge
when you transform to frequency space, and then lots of space is
wasted on them to keep the border sharp. Technically, if the black
border starts/stops exactly on a 16 pixel boundary you should be safe,
but it's much better to crop it.

Also, black borders make it impossible to play the movie on slow
computers since lots of memory bandwidth is wasted copying nothing.

Rich