need help - first animation

Im doing an short animation for an assignment but when I upload it to youtube, I dont get 16:9 ratio but 4:3 instead.

I used Adobe Flash Pro CS6 to make the animation, Swivel to convert .swf into .mp4 and then uploaded it afterwards. But I still get 4:3 when the canvas is 720x480..

Is there anyway for me to fix this? Thank you!

If this is in the wrong section, Im very sorry..



http://www.youtube.com/watch?v=0Yp76tKj4SI

There is no audio on purpose.

 

i thank youtube compresses it and it might be changing the aspect ratio.