Convert x264 (mkv file) into XVid with FFMPEG.

Example:

 ffmpeg -i Lockout.2012.x264.BDRip.720p.DUB.mkv -threads 4
        -vf scale=720:576 -aspect 2.40 -c:v libxvid -r:v 24
        -q:v 3 -c:a libmp3lame -ac 2 -ar 44100 -ab 128k -y Lockout.avi