iOS - Video resolution on retina display?

Question

I am embedding local, short videos inside my app. The size of the video (width and height) are predefined to fit the view they will be played in.

Edited Let say I have a video 800 height & 650 width.

I want to display it in the iPhone on a 400 * 325 view, so i resize it to this size. Should I make an other version of 800 * 640 for the retina iPhone?

What are the rules for video resolution on retina display deices? will I benefit a better video on retina if I will double the resolution?

Thanks

Shani