Audio files typically use the suffix common for certain format (MP3, MP4 etc.), but sometimes software developers use unique file extensions, even just audio.
AUDIO file extension - Game sounds or other audio data
What is audio file? How to open audio files?
File type specification:
File extension audio is occasionally used in some small programs or indie games for files that contain music, sound or other audio data.
In most cases these files are actually in one of the common formats like MP3, MP4 or FMOD, but sometimes are encoded slightly differently and had their file extension renamed.