Here are the extensions that are currently supported on the web and mobile devices.

Web: MP4, WebM, Ogg, MOV, m4v (All H.264 codec)

Mobile: MP4, WebM, Ogg, MOV, m4v (All H.264 codec) or mp4 with H.265 codec

Note: The H.265 codec is supported on limited devices and the extenstion must be on MP4 format.