Here is an example of someone who has posted a link to another YouTube video in a comment: https://www.youtube.com/watch?v=8kPyrq6SEL0&lc=z13qe524mnnzzzl5f04cdnrhgy3vi1zjk50
I tried to post a link to a video, but when I view the comment in a private browser session, it's hidden.
Best Answer
By default, comments with links are held for approval. The video owner must approve your comment in order for it to be shown.
https://support.google.com/youtube/answer/4409780?ref_topic=6011167