Feature: Automatically fade volume sliders

[bencodrington]

Users have suggested the ability to select a point on a volume slider and have the corresponding volume handle gradually fade to that point over a specified period of time. e.g. select '10s' for the length of time, and '50%' for the target volume, and then have it automatically fade to 50% volume over the next 10 seconds.

What would be the best way to implement that kind of UI in a succinct and elegant way that's viable on both wide and narrow resolutions?

Maybe by pressing and holding on the handle, then sliding left and right to set the target volume, and up and down to set the length of time?