I posted a video on Youtube and after a few days regularly indexed it suddenly disappeared from Google Search.
The video is original, the description is long and original, I don't think that it is overoptimized. This is the video https://www.youtube.com/watch?v=3yxyNx4JFgM
I just add a couple of comments to Youtube video, but I didn't started any link building campaign.
In spite of that after a few days online the video was almost de-indexed
I'm starting a few projects on Youtube, so after this first task, if you are a real Youtube SEO expert, we can collaborate together a lot