Beets - Music library manager and MusicBrainz tagger

Beets is the media library management system for obsessive-compulsive music geeks. The purpose of beets is to get your music collection right once and for all. It catalogs your collection, automatically improving its metadata as it goes. It then provides a bouquet of tools for manipulating and accessing your music.

Its features include

• Fetch or calculate all the metadata you could possibly need: album art, lyrics, genres, tempos, ReplayGain levels, or acoustic fingerprints.
• Get metadata from MusicBrainz, Discogs, and Beatport. Or guess metadata using songs' filenames or their acoustic fingerprints.
• Transcode audio to any format you like.
• Check your library for duplicate tracks and albums or for albums that are missing tracks.
• Clean up crufty tags left behind by other, less-awesome tools.
• Embed and extract album art from files' metadata.
• Browse your music library graphically through a Web browser and play it in any browser that supports HTML5 Audio.
• Analyze music files' metadata from the command line.
• Listen to your library with a music player that speaks the MPD protocol and works with a staggering variety of interfaces.