A custom-made continuous audio cartridge used in the Disneyland Main Street Cinema. The Cinema was part of Disneyland from its opening in 1955. Originally, it played classic silent movies, but, starting in the 1980s, it featured a varying selection of six classic Mickey Mouse cartoons, including cartoons like Plane Crazy and The Moose Hunt. Five were shown without their original sound while generic background music on a cartridge like this one played continuously in the cinema. The sixth—Steamboat Willie— was shown with its soundtrack. Both the soundtrack and the background music were played at the same time, as can be heard in the YouTube video.

I'm not sure why the cartridge was custom-made—maybe because the music would be played constantly day in and day out. The mechanism is extremely simple—it has no springs or other moving parts beyond the reel itself. There's not much to go wrong. The transparent plastic cover shows the state of the tape clearly and a single screw holds it together, which would have made replacing a broken tape fairly easy.