How to change video aspect ratio (ffmpeg)?

Hi there,

How can I change the aspect ratio of the video files uploaded/converted by ffmpeg?
They are default 4:3, but i need them to be 16:9.

I found some settings in this file:
\ray\modules\movie\inc\functions.inc.php

Convert function:

$sTempFile = $sUserId . TEMP_FILE_NAME;
$sInput = " -y -i ";
$sSize = " -s " . VIDEO_SIZE . " ";
$sRate = "-r 25 -ar 44100 ";
$sQuality = getSettingValue($sModule, "sameQuality") == TRUE_VAL ? "-sameq " : "";

Can I change the aspect ratio in this lines, or put a other default resolution in it?
Would be nice if somebody could help me on this?

Update:
FFmpeg seems not to be responsible for this problem, because the flv's in the /movie/files are the correct resolution and aspect ratio. But in the player the videos are still viewed squeezed..