If I’m not mistaken, as a container format, MP4 videos should be able to contain videos that are 480p. Also, from what I am able to find, the MPEG-4 video format does not have a limitation that prevents 480p either.
Yet, MP4 videos on YouTube are only available at 360p, 720p, and 1080p, and 480p is only available as FLV or WebM (regardless of the video).
Am I missing something? At 4:3, a 480p video would need to be 640x480, but at 16:9, it would be 853.333…x480. Could that be the problem? Is there a tangible limitation preventing 480p MP4s?