An NBS file contains an audio project created by Minecraft Note Block Studio (NBS), a third-party program used for making custom music for Minecraft. It stores "note blocks," which are musical notes that are organized to be played back as a song in the game. NBS files also contain metadata about the song, such as the song name, author, and length.

You will most likely only encounter NBS files if you play Minecraft and are creating custom music for the game with Minecraft Note Block Studio. While the files can be played back in the software to preview the music, they must be exported to the .MID format or to an MCEdit .SCHEMATIC file for inclusion in the Minecraft game. Along with note blocks and metadata, NBS files may save one or more tracks, which are known as "layers." The files may also store information about custom instruments featured in the song. NOTE: Minecraft Note Block Studio can import .MID files, so Minecraft users often use this feature to convert favorite MIDI songs and import them into Minecraft.