Steven,
Thank you very much.
I think this is a major improvement on the menu/min/max etc buttons. It just feels so much lighter and clean.
With the play-bar always showing, I think it is a very nice looking implementation but its background could be a bit lighter so that there is not such a sharp distinction between that and the main background (Unless this is what you are going after).
In cases like below, the smoother transition should prevent it from feeling like 'something is wrong'.

When the visualizer is visible, the visualizer space background could be more subtle. (It seems as though we had overcome this issue in the previous setup, but I do not recall). The gradient used there seems a bit rough, but I do not know if we could overcome that.

When the playbar is auto-hidden and the visualizer is in use, I realize that when one hovers it feels as if the player has frozen, because of course the visualizer is buried and not frozen.
Finally, I thought I would post these images below to see if there is anything we can pick up for handling transitions with lighter colors.:


They are not lazy... just more efficient.