[MPlayer-users] DVD rip Crop & scale little problems

[JiHO]

Alain Barthélemy wrote:

> Thus how can I calculate manually the cropping and rescaling of the image? Or
> is scale=576:-2 the right way to do it?

don't you want to use the "autoaspect" option of mplayer?
do you absolutely want to scale down the movie?

if the answers are no and yes, in that order ;), the solutions I see are:

Crop and take care of the "16 rule" while scaling:
1/ use cropdetect and check that even the half black pixels of the edges 
are taken of. after that you come with cropping dimensions to feed to vf 
crop.
2/ play the dvd with mplayer dvd://1 -vf crop "your_dimensions"
in the output of mplayer you can see a line of the form:
VO: [xv] 706x426 => 1004x426 Planar YV12
if you are using xv for example.
3/ from this line you know which dimensions are to be used in order to 
have a correct aspect ratio: they are 1004x426 in that example. you can 
use a simple factor to scale these down to what you want. let say 576.
1004 -> 576
426  -> ?
the height should be: 426 x 576 / 1004 = 244,4 = 244
4/ then the problem is that the height is not likely to be divisible by 
16. you must choose the nearest 16 multiplier which is 15 x 16 = 240.

With this solution you loose no pixel of the video and you distort a 
little bit the scale. nevertheless, if the nearest 16 multiplier is 
close of your calculated height, you are likely to notice nothing.

Crop and care about the 16 rule before scaling:
same first three steps, then
4/ modify your cropping so that the calculated height is divisible by 
16. I looked for a formula that will allow you to calculate it easily 
but I can't find a solvable equations system. so I guess it's just trial 
and error.

With this method you are likely to crop much more than needed of the 
video but your output's scale will be perfect.

hope that helps.
-- 
JiHO
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   Windows, c'est un peu comme le beaujolais nouveau :
à chaque nouvelle cuvée on sait que ce sera dégueulasse,
     mais on en prend quand même, par masochisme.
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