Liner notes (the booklet included with a CD) can be excellent sources of information on composers, musicians, genres, musical styles, and more. These databases include full-text liner notes, along with streaming audio and video:
Provides streaming audio access, original liner notes, and essays from New World, Composers Recordings, and other independent labels with an emphasis on American music.
Provides streaming video access to a collection of opera performances, captured on video through staged productions, interviews, and documentaries.
Collection of streaming jazz music with thousands of artists, ensembles, and albums.