Upload a video that's 480x270 (16:9) and go to watch page in MMM. Go to embed window.
Dimensions provided are 620x449, 540x404, 460x359, 380x314, 300x269. (16:11.6?, 16:12? ????)
And, it won't let me change to the ratio I want. If I type in 480 for width, it puts in 370 for height (16:12.3). If I try to change height to 270 , it changes the width to 302.
It provides variations on 16:9, and lets me put in whatever I want for custom size.