It’s no secret that I like building music visualizers, or that I’ve been playing with HTML5 a fair amount lately. Given that, I thought I’d combine the two interests, and build a music visualizer using JS, the canvas & audio elements in HTML5, and the EaselJS framework.

The primary challenge was that Javascript doesn’t have any built in mechanism for accessing the volume of a playing audio tag. To address this I wrote a little AIR application that will read an MP3 file using Sound.extract() and export peak volume data as a text or JPG image file. I then wrote a JS class called VolumeData.js that reads in these files and provides access to the data via a simple interface (ex. myVolumeData.getVolume(time) ).

With those pieces in place and tested, I started putting together a demo of it in action using EaselJS. Two of the newest features were compositeOperation support (which let me approximate an “add” blend mode), and the drawPolyStar method, both of which I used to excess.

I think the end result is pretty cool, though it requires a fairly modern system, and will still melt your CPU – I was intentionally pushing things hard to try to find the performance limit. It requires an up to date browser to run.

I built two variations: Star Field and Atomic. Occasionally dynamic audio loading seems to break on certain browsers, just reload if it gets stuck on “loading music”.

If you’re interested in building your own music visualizers in HTML5/ Javascript, you can download the demo source, VolumeData.js class (MIT licensed) and VolumeData AIR application here. Also, be sure to check out the latest version of EaselJS (we just released v0.3.2 today).

Please let me know if you build anything cool with the code. I’d love to see it.