1. Go to the video info:
2. Scroll down to the section for "Whitelist"
Here you can see your recently used URLs or just set a new one.
Now comes the magic.... You could for example add Twitter and your own website and then the video can only be shared / embedded to those two websites.
You could create a section on your website where people have to log in and then just embed the videos there. If someone else were to embed the videos on their site, it would only show an error.
TIP!
To put on the finishing touches, keep the video in the video state “unlisted,". This way it won’t even be visible on alugha.