Update (2015-11-23): Spotify has this! Check out Spotify Running for tempo-based playlists and automatic tempo calculation.
Someone, somewhere has the metadata and music chops to deliver BPM-based radio streams. DJs and gym rats will follow. A couple ideas.
The closest are Echo Nest’s API (
get_tempo) and Last.fm’s API (
Track.getInfo). Echo Nest’s requires uploading the song audio data (which I don’t have). Last.fm’s can be queried with metadata (artist+song name) yet doesn’t provide BPM. This NYTimes Gadgetwise blog post has local file (MP3) and podcast options.
I prefer to exercise to music, and it’s much nicer when the beats per minute matches what I’m physically doing. I think this could happen 3 ways:
Faster/slower tempo adjustment of any station. This could be a really awesome subscriber feature.
Adding BPM as a new radio station “station type” (from http://www.last.fm/api/radio and exposing it in the UI as a Tempo dropdown. For example: lastfm://bpm/140
A third party app which creates/queues a playlist based on BPM. This would be almost entirely doable with the existing API (get similar artists, add to playlist) if
There’s lots of docs for estimating BPM for a bitstream, but short of someone with a huge music collection, Last.fm would need to pregenerate them and expose it in the API. This API is particularly well thought out: http://developer.echonest.com/docs/method/get_tempo/ (but it too needs the bits; it’s not an existing database).
Mass BPM calculations would be a killer use for Map/Reduce.