Next Button: Inactive til Audio/Video Completes?

Hello there: 

My stakeholder wants to mandate that users complete hearing the audio on a slide (or in some cases, watching the video) on a slide before they are able to move on in the course. 

They do not want: 

a) the next button removed all together from the player, and auto-advance to next slide when audio done.

b) an inserted next button on the actual slide that appears when the audio is done, so they can click to continue (and the next button is removed from the player in this option, too).

Is there a way to make it so that the next button in the player is NOT active until the audio completes? If so, could I please see a demo of this? I cannot figure this out -- have consulted 2 other designers, and they both suggested A and B above...

Thank you for your help!! 
Gabriella 

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