I use Coverart to display whether a movie is HD or SD.
I have many 720p movies that might have been 4:3 originally. After the margins have been trimmed, the resulting 720p file has a width less than 1200. That appears to be the cut-off where CoverArt decides whether you have an HD or SD movie even though Emby labels it 720p.
Many movies end up with a width in the 960-1199 range that are clearly 720p (HD). A 4:3 720p movie will have a width of 960. On the movie's page, Emby displays