[MPlayer-users] Re: mencoder: ripping a dvd to a 700MB avi questions

Jason Lunz lunz at falooley.org
Fri Jul 5 16:01:01 CEST 2002

bugfood-ml at fatooh.org said:
> (Approximately, of course). So, cropping the X axis to 366 pixels and 
> then scaling down to 309 would be the minimum ideal. The nearest 
> multiple of 8 above 309 is 312, which means either scaling straight from 
> 366 to 312 (the aspect ratio is _very slightly_ messed up) or not 
> cropping as much so the scaling works out (a bit more math involved). I 
> choose the latter.
> 312 / 0.843 = 370
> -which means that if I crop to 370 the scaling will make the X 
> resolution a multiple of 8. 366 and 370 differ by 4 pixels, so I leave 
> 2-pixel bands at the top and bottom. Thus, the scale/crop section looks 
> like this: -vop scale=720:312, crop=720:370:0:52

When faced with this choice, I usually choose to _overcrop_ on the
theory that I'll get better compression. The videocoder not only has
fewer pixels to encode (because you've thrown away a narrow band at the
top and the bottom), but it also doesn't have to spend bits on
representing the transition from movie to black.  I'm under the
impression that it's things like edges and detail that stress an
encoder, so removing that black transition from the top and bottom of
*every* frame can only help. And no one's going to notice a couple of
pixels missing from the edge of the frame.


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