FLAC format.

The sound quality of car music depends on many factors, including the quality of the car audio, the performance of the playback device, and the format of the audio files. FLAC is a lossless compression format that can completely copy the audio information on a music CD into a digital music file, thus retaining the integrity and authenticity of the music. Therefore, the FLAC format has the best sound quality, which is comparable to CD sound quality.