Hey.
Now it works fine. I am playing a (rather) small set of mp3's.
I really like the toolbar interface. Everything looks good.
I am not too keen on your volume control. I prefer the slider to be visible, as the button-thing seems to add another step to changing the volume.
The texr-only toolbar is pretty useless, as it only opens the buttons when pressed. In my opinion lose it. Or make it a hide toolbar thing.
The small icons selection also seem redundant as the difference is very small. My opinion lose it or make the standard icons bigger.
Another piece of input. It would be great to make the currently playing song more visible. I mostly use cog for audiobooks, and often the tracks are called 1, 2, 3 etc. and they are quite hard to distinguish from the not playing songs (maybe a feature request).
Overall, looks good.
Happy working
Zitz