Google updates its search algorithm frequently. For example, on February 23rd, 2016, Google made significant changes to AdWords, removing right-column ads entirely and rolling out 4-ad top blocks on many commercial searches. While this was a paid search update, it had significant implications for CTR for both paid and organic results, especially on competitive keywords.

What about subtitles & closed captions? I see in one of your comment replies that you’ve uploaded transcripts of your videos but looks like Youtube has 1 spot for transcripts and another for subtitles/CC. Have you tested both transcripts and subtitles/CC? Also, I know the difference between subtitles and CC but there doesn’t appear to be anyone that’s tested once vs the other. Might be something to test.

I followed your recommendations but faced some strangeness in video rankings. I have launched a channel on youtube a week ago. I have already uploaded and optimized 3 videos for “video keywords”. And so far i have a situation: two of my videos are ranking high in Youtube (1st and 5th position) but non of them are being shown in Google search results. But at the same time google shows up to 10 video results for those keywords. Do you have any ideas why? Really appreciate your help.
Meh, I disagree with your theory about using less tags. You should use all 500 characters for optimal results. There is no proof that likes/dislikes does anything to the SEO. I’m sure that is more for the content makers info and viewers warning. The description can be up to 5000 characters. Best to post your other video links. You have no proof of anything, noone does, we can only guess how youtube seo works..
Google’s aim is to provide the most relevant result for any given query. Their entire business model relies on them being able to do this, consistently, across hundreds of billions of searches. For that reason, they’ve invested heavily into understanding the intent of queries, i.e., the reason a person typed a specific thing into Google in the first place.