The capture cassette is a special N64 cartridge that plugs into the top of the N64. It features a composite cable output on the back along with a microphone port. The microphone was included with the capture cassette.
The capture cassette's main use is within the Mario Artist series
In Mario Artist: Paint Studio, the player can use the capture cassette to import images into the game. They can also use it to export the created images out of the game.
In Mario Artist: Talent Studio, the player can use the capture cassette to export the movies that they created, import pictures of faces for use in the movies, and record audio with the microphone.
In Mario Artist: Polygon studio, the player can use the capture cassette to import textures and 3D models to be used within the game. It can also be used to export the player made models.