Possible solution to videos not playing (and quests sticking as result)

This ‘fix’ is for those who do not own an N version of windows.

Head to; https://www.codecguide.com/windows7_preferred_filter_tweaker.htm

Download Win7DSFilterTweaker from the page
Run and check ‘Media Foundation’ codecs aren’t being overridden
(Specifically x64 and .mp4)
If the box is checked, it’s being overridden - uncheck & save.

codecs

No need for codec packs and reversible if it breaks your x264 decoder of choice.

Hope that helps.

Note: My stuck quest proceeded after the video was fixed, no need to restart.
Good luck.