[MPlayer-users] Converting 512:272 to 480:480 with aspect=4/3?
romildo at uber.com.br
romildo at uber.com.br
Sat Jan 17 17:37:06 CET 2004
On Thu, Jan 15, 2004 at 07:07:11PM -0500, D Richard Felker III wrote:
>
> On Thu, Jan 15, 2004 at 11:54:32PM +0100, Svante Signell wrote:
>
> > Need advise hoe to expand/scale/crop an avi clip of size 512x272 to an
> > mpeg2(SVCD) clip of size 480:480 expanded to 640:480 when displayed.
>
> You have to do the math to work out the right sizes,
Is the math the following?
width ------------------ height
640 ------------------ y
width * y = 640 * height
y = (640 * height)/width
In the example above of a frame size 512x272 we have y = 340.
> or else get
> mencoder to do it for you with fancy use of the automatic options for
> scale.
How would that be achieved?
> Try:
>
> -vf scale=480:340,expand=480:480
-vf scale=480:y,expand=:480
> Actually you should fudge the vertical scale slightly so that black
> borders end up _exactly_ at multiple-of-16 boundaries (in this case,
> scale to height 336 instead of 340) to maximize quality, but the above
> commandline will at least work.
That is not much clear to me. You say that the black borders should
end up exactly at multiple of 16 boundaries. What exactly a multiple
of 16 boundary mean?
0 -> +-------------------------------------------+
| |
| (top black border) | 70
| |
70 -> +-------------------------------------------+ <- boundary ?
| |
| |
| (movie image) | 340
| |
| |
410 -> +-------------------------------------------+ <- boundary ?
| |
| (bottom black border) | 70
| |
480 -> +-------------------------------------------+
Is a boundary an offset in the vertical axis?
Are the boundaries in the example 70 and 410? If so,
you are right. They are not multiples of 16.
Using a height of 336 instead of 340 will give the
boundaries (480-336)/2=72 and (480-336)/2+336=408, which
are not multiple of 16 neither.
In the example given, you say 336 is better than 340.
I see that the image height (336) is a multiple of 16,
but each black border height (72) is not. Is it
enough that the image height be a multiple of 16 to
get maximized quality?
Regards.
Romildo
PS: Which scaling method do you suggest for a good
speed/quality compromise?
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