How to convert a video to 4:3 or 16:9 aspect ratio without loss of video quality

Question

I uploaded my video to youtube and the highest resolution it appears as is 360p. This is much lower than what I uploaded. I believe that youtube isn't making higher resolutions available for my video because of its aspect ratio. The video is 720x400. How can I convert this to a different aspect ratio without losing any of the picture or picture quality? I don't care if blank space appears around the video so long as the picture doesn't get stretched horizontally or vertically.

Answer 1

try ffmpeg

ffmpeg -i mymovie.mpg -ar 22050 -acodec libmp3lame -ab 32K -r 25 -s 320x240 -vcodec flv mytarget.flv

ffmpeg has also option i.e.: -aspect 16:9