[MPlayer-users] Re: mencoder/crop => image distortion

ROED,HAAVARD (HP-Norway,ex1) haavard.roed at hp.com
Thu Jul 31 13:10:18 CEST 2003

> From: D Richard Felker III [mailto:dalias at aerifal.cx]
> > 
> > 1. Round up to nearest acceptable Y, ie leaving (thin) black bands
> > above/below
> > 2. Round down ..., ie cropping a bit of the actual movie
> > 3. Crop and then rescale the movie for the encoder
> > 
> > None of the above yields satisfactory results, since #1 
> propably affect the
> > macroblocks and still consumes bandwidth due to edges, #2 
> obviously is not a
> Yes, #1 is a very horrible choice unless you want to make a 3- or 4-cd
> rip.

Good, then I atleast have gotten -something- absolutely right.

> > brilliant solution (to me, atleast, I want the whole thing, 
> not "most of
> Cut the perfectionism. Encoding a movie with lossy compression is not
> about getting a perfect quality copy. If you want to do that, rent the
> film reel and duplicate it.

True, but I'm in a learning process where I want to get the most out of
MEncoder/MPlayer, which is why I may be "dissing" methods you learned people
know to be the best. I'm not looking for a replica; if so, I wouldn't use
(lossy) compression, but make... well... replicas. I'm trying to figure out
how to use MEncoder to achieve maximum quality at any given

> > it"), and #3 would modify the aspect ratio, "mangling" the 
> original movie.
> > Scaling except in a player seems like a bad idea to me anyway.
> Why? This is nonsense. The standard way of dealing with movies that
> don't naturally come out to a perfect size is to scale to the nearest
> multiples of 16. Then encode the actual perfect aspect in the mpeg4
> headers, if you care, but no one will notice the difference anyway.

I was referring to the DOCS, section 7.3:

"Often the need to resize movie images' size emerges. Its reasons can be
many: decreasing file size, network bandwidth, etc. Most people even do
rescaling when converting DVDs or SVCDs to DivX AVI. This is bad. Instead of
even you doing so, read the Preserving aspect ratio section."

Which is why I've been assuming rescaling is a bad thing.

> > (Particularily since the new aspect cannot be saved in the 
> resulting file,
> > except for the proprietary MPlayer tag.)
> It is NOT a proprietary tag!!! It's in the mpeg4 standard!!!!! Crappy
> windows players just suck too much to read it.

Continuing with the DOCS, section 7.9;

"MPEG4 has an unique feature: the video stream can contain its needed aspect
ratio. Yes, just like MPEG1/2 files (DVD, SVCD). Regretfully, there are no
video players outside which support this attribute. Except MPlayer.

This feature can be used only with libavcodec's mpeg4 codec. Keep in mind:
although MPlayer will correctly play the created file, other players will
use the wrong aspect ratio."

lead me to believe that since the claim is that no video players except
MPlayer supports this attribute (the aspect ratio tag), this was MPlayer
proprietary tag. I understand now that it's a MPEG4 specific tag, but then
how can MPlayer claim that no other player supports it?

Now, to further explore this issue, I note that the ability to add this tag
is valid only when using libavcodec mpeg4 (DivX 4/5 only?). Which I'm not -
I'm using XViD, thus I stick to my previous "conclusion"; that #3
(rescaling, changing aspect) is a bad choice (when not using libavcodec).
Since XViD is in fact a mpeg4 codec (or at least claims to be), I would
expect it to support the mpeg4 aspect tag :( And finally, when a player is
able to play ie mpeg4 video, it would be nice if it actually supported the
-whole- standard.

> No one produces movies at 720x576.... The people doing this have much
> higher-end tools and don't really care how well it compresses, since
> they probably edit uncompressed video on huge clustered machines...



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