So very cool. Someone has made videos which show which instruments are playing which notes as the music plays. Some examples:
These appear to have been done by the same YouTube user, but their page doesn't seem to link to all of the extant videos. (Warning: that page starts playing The Stars and Stripes Forever after a few seconds!) There does seem to be a playlists page, though, which gives a thematic/historical categorization and includes more of the recordings.
(I discovered these videos via Kristin Cashore's blog.)