Get Relative Loudness Of Song, Javascript

I'm trying to build an mp3 player for my site using JavaScript (and any plugins/frameworks(jQuery)/libraries that are relevant) & html5. So I built the player (more accurately,

Solution 1:

You would need to be able to decode the MP3 yourself. The html5 audio element, and the browsers's implementations of it, don't expose this sort of data. For example, look at Firefox's exposed methods for JavaScript. The closest thing to what you want is the "volumechange" event. But that is in reference to the volume mixer on the browser's rendered control (i.e. output volume). It has nothing to do with the actual dB of the audio source.

I imagine that the only feasible way to do this is to render your waveform to a graphic ahead of time, and then "reveal" it as the song plays (e.g. with the "timeupdate" event).