I am a bit baffled as to why Google suddenly deindexed my videos, seemingly, so I inspected the provided reasons in search console (Previously known as webmaster tools), and the specific reason given was: Video outside the viewport.
That is not really sufficient reason not to index a video, and at the end of the day Google will just be eroding the quality of their own search results if they completely deindex such videos. It makes sense to down-prioritize them by making them rank lower in the results, but de-indexing them completely will just make them harder to find for users.
I can see the value in having a video placed within the viewport, but only when the video is the primary content on the specific page. It indeed might not be the primary content when used as part of a tutorial, but that does not mean the video has no value for searchers.
Hopefully it will get rid of "fake" video pages from the top search results though, because when doing a video search only to have pages returned with the videos hidden deep within the content – or sometimes even outside the main content block – is quite annoying. If people are searching for videos, then it has to be somewhat intuitive how to quickly get to the video, and I guess "video-within-viewport" is just a simple way for Google to get to that end goal.
Sometimes you just gotta shrug your shoulders and move on. This particular indexing issue is not worth spending time on solving. If I have videos that are actually intended as the "primary content", then I will probably use a layout similar to YouTube for those specific pages, as that is certainly more user friendly.