Sorry I don't get it... 

There is no check before calling drawer.clearSelection(mark0, mark1).. or I'm missing something...

Just click on the waveform in your website (http://www.wavesurfer.fm/) with a js console opened and you will see this : 

![js_error](https://cloud.githubusercontent.com/assets/6024701/2982288/2807ec50-dc13-11e3-8d9c-63591941b7d9.png)

Am I missing something ?