Better banner file formats

Please allow uploading of banners in MP4 format, which is already used for media labeled as “gifs”. Tenor files are frequently delivered in such format. Ideally WebM would also be allowed, as I find it better (even if a “gif” hosting service converts it to MP4).

These formats are vastly superior to GIF and PNG for animated images, as their video compression allows for far longer or higher-quality animated images. What GIF can do in hundreds of megabytes, WebM can do in five.

With a bit of thoughtfulness, file space usage could be improved further by preventing resize of media when resizing increases file size (which happened with my profile banner; it also lowered quality).