Scaling optimal video frame dimensions I'm trying to setup my site to store uploaded user content in a 640x360 frame size, which will be presented back for viewing in that frame size and in a smaller frame size.

I'm trying to understand why this site (and others): http://www.encoding.com/what_are_the_best_flash_video_frame_dimensions recommend only the following values for smaller sizes:

384 x 216
128 x 72


when clearly others like:

320 x 180
256 x 144


also exist.

What is the mathematical reason behind recommending only these frame sizes?
According to the site you referred to:
http://www.encoding.com/what_are_the_best_flash_video_frame_dimensions

The math behind the "Best, Better, and Good" video formats are based on if both Horizontal and Vertical pixels are divided by 16 for best, 8 for better, and 4 for good.

Therefore 256x144 is best, while 384x216 &amp; 128x72 are better, while 320x180 is good.