[UX] Fix Issue 1238: Videos sounds can play over each other (#1266)

Fix issue #1238

This is a Draft - current solution seems fairly robust - scroll away & video stops; scroll back & it starts over -

...but still investigating potentially more robust solutions i.e. whether it could be more responsive / sensitive to scrolling away even at higher scroll speed (as in below demo)

Demo video of current fix in this post: [~1 min. / 50MB]

UX-DamusVideoPlayer--Fix-Issue-1238--Videos-sounds-can-play-over-each-other, 1 commits