I'm not sure what solution they're looking for. A single universal volume control where if you turn up a video it means your ringer is now on full blast? 6 volume buttons on the side of your phone to adjust them each individually?
Android's system of adjusting media volume when media is playing and ringer volume when it isn't seems like a reasonably clean solution. It takes a single tap to expand to the three sliders.
Maybe a shortcut where where pressing volume up/down simultaneously mutes everything?
It's not that exotic, you've got a child or a sleeping partner or a boss in the same room and you want to watch a mostly visual video without any unnecessary jingles or other audio cues from disturbing them.
So you reduce the volume, but it only reduced the ringer for calls, which isn't what you want.
As the sibling answer says, newer Androids can do this. One click to display the volume, a touch to see the individual controls and then slide.
1) Press volume button to bring up volume controls
2) Tap the arrow on the right to expand
3) Adjust ring/music/alarm volumes as needed: http://core0.staticworld.net/images/article/2015/05/android_...