.UST File Extension
What is a UST file?
File created by UTAU, a vocal synthesizer similar to YAMAHA's VOCALOID and VOCALOID2 software; supports musical notes as well as dynamics, vibrato, pitch, and lyrics; often used for storing music for Japanese vocal androids, or "vocaloids," which are synthesized voices often used by sing and dance games.
UST files can be played back in the UTAU, and they can be exported to MIDI (.MID) or VOCALOID (.VSQ) formats or rendered to a .WAV file. UTAU can also import VSQ and MIDI files and convert them to UST files.