DVD Annotations

Lots of DVDs allow you to watch the movie with or without subtitles. Of course, the DVD doesn't contain two copies of the movie --- it has one video track, and the subtitles (if selected) are overlaid on the video by the decoder. But why should we be limited to the subtitle tracks present on the physical disc? I should be able to download a set of subtitles from the net and tell the DVD player, "here, use these".

This would be useful for foreign movies which haven't been officially released in English. A lot of anime, for example, has fan-written translations available, but it should be possible to put these translations onscreen and automatically sync'd with the video. MST3K-style commentary would also be possible (as I understand it, the DVD overlay format allows shapes as well as text). Other uses include director's commentary, film-school instructional commentary, glosses and explanations for films from a distant culture (maybe the movie is in a language I understand, but from a time or place that is unfamiliar to me). You could even subtitle an English film with different dialogue (say, to make The Matrix or Star Wars Episode One less painful) or, with more effort, supply an entirely new audio track. Since these "annotation" files wouldn't contain any part of the original movie, they should be perfectly legal to distribute.

Although I doubt Sony will come out with this feature any time soon, there's no technical reason it should be difficult. Now that open-source DVD players are becoming usable this idea may be bakable.