How can I tell iTunes that a .M4V (movie) is an HD movie? HD movies that I buy from iTunes appear in iTunes with the movie's name and a little "HD" symbol next to the movie. However, movies I've ripped from my BluRay discs, which are HD, aren't recognized by iTunes as being "HD". Of course they play fine via iTunes or AppleTV, in HD and everything, it's just I'd like to somehow edit the metadata or whatever it is that iTunes uses to identify a movie as being HD. I know it's just cosmetic, but it irritates me!
There is an HD flag you can set in the file's header. You can't set this flag from iTunes.

The best solution on mac is subler.

It was updated to support the 1080p value, so you can set the flag to 1 (720p) and 2 (1080p), the only values recognized by iTunes.

You will find the flag in the other settings tab: