YouTube Creative Commons videos

When you use a creative commons video in YouTube, do you have to put an attribution to the original video creator in the video description?

I've read that you have to, but I read somewhere else that YouTube already include an attribution link automatically, so you don't need to include one yourself.

If you use the YouTube Video Editor it will add this information automatically, else it's a good practice to
add the Source URL(s) if you [Upload] CC mixed or singular content.

I agree to give credit, I have done that a little and when I did it, I downloaded the video, mixed it a bit and then re-uploaded it so I could monetize it. Now I think that is ok as it is creative commons, though doing it through youtube, they do not let you monetize it after you are done with it using their video editing stuff.

Someone did write to me and complain, then they said, oh crap it was labeled as creative commons and that is all I heard from them