If you're using Chrome from the dev or unstable channels, you probably have a bad Flash plugin enabled (this affects HTML5 audio as well for some obscure reason).

To fix it, go to chrome://plugins and disable all the flash plugins. Then click +Details to show the individual versions of Flash, enable them one at a time until the problem goes away.

This is the configuration that worked for me:

If you none of the versions you have work, you may need to install the adobe-flashplugin package:

sudo apt-get install adobe-flashplugin