The Audio file formats for Spotify include the FLAC and WAV formats. It is good to use the FLAC format. When Spotify gets the audio files the Spotify team does the following things.
The team checks the track is clear and it isn’t corrupt and the format container is known. Then transcode the file into different delivery formats to ensure the audio quality.
Ogg/Vorbis, AAC, HE-AACV2, and then calculate the loudness of the whole release and individual tracks by the use of ITU 1770 standard. The Spotify team also encrypts the audio files before they deliver files to the platform.