Audio level slider does not change audio level while dragging

Note that this issue only appear in window mode. In fullscreen mode, the audio level slider works as expected.

Steps to reproduce:
1. Open a video with the Player
2. Drag the audio level slider for a while

Actual Results:
While dragging the audio level slider, the audio level is not changed.

Expected Results:
While dragging the audio level slider, the audio level should be changed (more or less) continuously so that the audio level slider does reflect the current audio level all the time.
Why? Imagine the user wants to lower the volume. He is now dragging the audio level slider to do so. Unfortunately, the user has no indication of how the audio level would be if he released the audio level slider at a given point. But how does the user know where the has to place the audio level slider to get the right volume if the only way to find out what the volume would be is to stop dragging?

Workaround (if any):