[MPlayer-users] mencoder: ripping a dvd to a 700MB avi questions
bugfood-ml at fatooh.org
Fri Jul 5 10:47:01 CEST 2002
Dominik Benninger wrote:
> [Automatic answer: RTFM (read DOCS, FAQ), also read DOCS/bugreports.html]
> On Freitag, 5. Juli 2002 01.17, Farrell Farahbod wrote:
>>no it doesnt, but i have some that do, and i forgot to ask how to crop
>>out the blackbars that result from dvd manufacturs that are too mean to
>>use anamorphic widescreen...
> use mplayer -voc cropdetect input.avi, but it's written in RTFM.
Actually, that's mplayer -vop cropdetect input.avi. (typo) :-)
Cropdetect tells the absolute maximum cropping, though, and as such is
only half the story: it's always best to keep the resolution as a
multiple of 8 (I've heard 16 is better, but I've never had trouble with
8). Anyway, this necessitates either scaling a bit differently or
padding the crop estimates slightly with very small black borders.
For instance, with a fairly typical 2.35:1 widescreen movie with bands
on top and bottom, the real resolution is 720x480, which is scaled up to
854x480. cropdetect might recommend crop=720:366:0:54 (with respect to
the real resolution).
On such movies I usually downscale on the Y axis rather than upscaling
on the X axis.
720 / 854 = 0.843
366 * 0.843 = 309
(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
I write down the end result each time I have to do these calculations,
so now I have sets of values for all the common resoluions - I just have
to tweak them slightly to compensate for movies that are positioned just
a little bit differently.
In any case, your preferences may vary, or someone will point out just
how wrong I'm doing this. :-P ...but you should at least have a basis
from which to start.
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