Video converter

Hey there,
What is the easiest way to decrease the aspect ratio of a video, without changing other things, as the sound quality or the video format, so that the picture would fit my galaxy s2 screen with less memory required i would greatly appreciate it if some one could recommend a program either working in android or Windows.

 

well, nobody answered, but at last i found my answer , moo0 videminimizer, free, stable and fast application