1280 pixels * 720 pixels * 30 frames per second * 12 bits per pixel (this would be 24 if the camera sends data in RGB and not YUV, that is, double) = 331776000 bits per second
Divide by 8: 41472000 bytes/second
divide by 1024*1024: 39.55... megabytes/second
Double that if it's RGB..