XSPF is an open-source music playlist format. It hit the bigtime this week when the Yahoo! Music Engine was released as the client for Yahoo! Music Unlimited. YME uses XSPF as its playlisting format. This is cooler and potentially a bigger deal than most people realize. Using an open playlisting format paves the way for various kinds of development (more on that in a minute). It's also smart on Yahoo!'s part, as that development will help distribute the Music Unlimited brand and YME experience.

One third-party extension that has already emerged is the MusicBlogs Publisher Web Plugin for Yahoo! Music Engine. When downloaded, installed, and YME rebooted, the plugin allows users to create and publish RSS feeds of their playlists. Anyone subscribing to the feed must have an XSPF-compliant music player (such as Yahoo! Music Engine or the open-source XSPF Web Music Player which can be bolted into Firefox). Thus equipped, anyone can listen to 30-second samples of the YME-derived playlist, or, if they are Music Unlimited subscribers, they can hear the full-song playlist. Music Unlimited users who really get into it can create entire blogs of one playlist after another—the blog entry is the playlist plus whatever commentary. Sound like podcasting? Well, it's not portable. But it is a legal, no-license-needed way of distributing one's musical taste.

This is extraordinary from Yahoo!'s viewpoint. To whatever extent things like this catch on, people will be strongly guided to the Yahoo! Music Engine to hear the music, and to Music Unlimited subscription to create their own playlist blogs.