I just figured out how to do this, and didn’t see any other mention on these forums, so hopefully this will help someone else.
mt-daapd can use bpm (beats per minute) in smart playlists. The faster/more energetic a song, the higher the bpm. For example:
bpm >= 140
for high energy, good for workouts, etc.
1. Add some smart playlists based on bpm
2. Use MixMeister BPM Analyser (free!) to automatically add the BPM information to your entire MP3 collection.
3. Rescan in mt-daapd
You can use the same method to find medium energy, low energy, etc.
Andy