I don't know how it turned up on the web, but here it is, a wonderful episode of Make Mine Music, The Whale Who Wanted to Sing at the Met.
With Nelson Eddy as narrator and singer, Whale tells the story of the Metropolitan Opera looking for the sea monster reported in newspaper headlines, because this monster sings beautifully. The "monster" is actually Willie, a whale who can sing in several voices simultaneously.
A friend of his, a gull called Whitey, tells him about the searching ship, and Willie goes to audition, as it's been his ambition to perform on stage. Unfortunately, Professor Tetti Tatti from the Opera believes that one or more singers have been swallowed by the whale, and need to be rescued — and there will be no spoiler here of the outcome.
Other episodes of Make Mine Music, the film entered in the 1946 Cannes Film Festival: Blue Bayou, Without You, Casey at the Bat, Two Silhouettes, Peter and the Wolf, After You've Gone, Johnny Fedor, and Alice Blue Bonnett. All the Cats Join In is a jazz interlude featuring Benny Goodman and his orchestra.