What is the audio file in the short message?

Music or something. This belongs to MMS.

You can accept MMS or send MMS.

Audio files are usually divided into two categories: sound files and MIDI files. The sound file is the original sound recorded by the sound input device, which directly records the binary sampling data of the real sound; MIDI file is a musical performance instruction sequence, which can be played through sound output devices or electronic instruments connected to a computer. Audio file is an important file in network multimedia.