[MPlayer-users] Re: mencoder/crop => image distortion
jonner at teegra.net
Fri Aug 1 06:17:30 CEST 2003
D Richard Felker III wrote:
>>Which is why I've been assuming rescaling is a bad thing.
> If you want to make a replica of the DVD, then it's bad, but like
> we've said that's usually not the purpose of encoding (if that's what
> you wanted you could just copy the .vob without reencoding). I'm not
> sure who added that paragraph to the DOCS, but IMO it should be
> removed. Scaling is pretty much ALWAYS required unless you want to
> make a 2-cd (or more likely 3-cd) rip, just because of bitrate
> considerations. So if you're scaling to begin with, you might as well
> make the pixels (almost) square while you're at it, unless that will
> result in a big waste of space (e.g. svcd, where you'd have to scale
> up to 640x480 from 480x480 -- that would pretty much negate the
> improved compression you get from using mpeg4).
That's exactly the policy I've used. I generally use mencoder
with lavc, scaling the movie to have pixels very close to square.
When I want to use a large frame size, I don't allow the
horizontal dimension to be scaled larger than the original (700 -
720 for a cropped DVD movie), so the pixels end up being slightly
taller than wide. I always add the aspect tag.
The result is that most of the movies will look correct in any
player, though a few will look a little odd in anything but
MPlayer. It is very disappointing that the aspect tag isn't
widely respected. I was especially disappointed to discover that
ffdshow (the DirectShow filter that uses lavc) doesn't respect
it, though it allows the user to manually change the aspect.
Maybe the author just isn't aware of it, so perhaps I should
submit a bug report.
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