Complex sentence: It was performed in the film and on record by Glenn Miller and his orchestra, vocal by Ray Eberle and Pat Friday, although unreleased recordings of the song were made in 1941 for possible inclusion in the film Sun Valley Serenade.
Split into simpler sentences: It was performed in the film and on record by Glenn Miller and his orchestra, with vocals by Ray Eberle and Pat Friday. Unreleased recordings of the song, however, had been made in 1941 for possible inclusion in the film Sun Valley Serenade.