You should NOT do that. It's a practice that google frowns upon.
The correct way to add keywords into the other parts of your product are through an appropriate title, a description that uses the similar/same keywords but in a legit, descriptive manner that explains the video and then in your keywords section try to make your keywords also match (order counts to some extent as well).
The way I do it is like this.
What's my video about? Call of Duty - Glitches
Tons of keyword research. I find my keywords. Let's say it's "call of duty" "glitches" and "gameplay"
My title would then be something like, Call of Duty Gameplay Glitches - A Glitch Montage
My description would then be something like:
I put together a huge montage of my favorite Call of Duty Glitches. While recording CoD gameplay over the years, I've built up quite a collection of hilarious glitches.
Then in my keywords, i put all that stuff in.
You do not want your description to be:
Call of Duty Glitches, glitches, cod, funny glitches, cod funny glitches, cod gameplay glitches, blah blah blah