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

[ROED,HAAVARD (HP-Norway,ex1)]

> I can't remember where, but I'm pretty sure I've read that 
> MPEG-4 video 
> can have dimensions that are multiples of eight. It may be 
> that modern 
> encoders have no problem with it, though older, less 
> compliant ones did. 
> I've been sticking with sixteen, since I know it works and it's not a 
> hassle anyway.
> 
> Jonathan Rogers

I'd like to stick to 16 too (or even 8, if thats a 'good' number), but what
if cropdetect says to crop the movie at some odd dimension that's divisible
by neither 16 nor 8, or even 4 (or 2) if those numbers work with encoder "X"
version "Y", ie 720:549.

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
brilliant solution (to me, atleast, I want the whole thing, not "most of
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.
(Particularily since the new aspect cannot be saved in the resulting file,
except for the proprietary MPlayer tag.)

If I were to scale the encoded movie, does something like -vop
scale=720:560,crop=720:549:0:11 make sense? (the numbers are fictional, and
for illustration purposes only - the point being that the cropping is done
exactly at the edges of some funky movie with 11pxl black band above 12pxl
below)

Finally, I guess it's the actual production of the movie that leaves us with
problems such as these; In a really good (new, digital, precise) production,
I guess cropping always can be done in sensible (ie. encodable) dimensions.

Haavard