[MEncoder-users] calculating SCALE

[RC]

On Wed, 24 Aug 2005 12:38:41 +0200
Tomáš Bažant <tomas.bazant at rozhlas.cz> wrote:

> thank you for this method, and then: how does mencoder calculate it 
> then? i need the equation genrally...

You calculate the height by dividing the width by the aspect.  eg.
640 / (4/3) = 480  Calculate the width by multiplying the height by the
aspect eg (4/3) * 480 = 640

It's complicated to do it manually, because a filter chain can require
a change of the aspect repeatedly, due to cropping and scaling.

Calculating the new aspect after cropping (high precision needed to
prevent noticable rounding errors):

(OrigAspect) / (OrigWidth/NewWidth) * (OrigHeight/NewHeight) = NewAspect