I have the opportunity to direct a music video and I'm not sure if I want to take it
That sounds exciting though. Why wouldn't you want this opportunity?
Because I'm afraid I will not be able to grasp what I'm supposed to do.
It's totally normal to feel a bit uncertain about a big event like this.  I say have some faith in yourself and go for it!
Ok, I will do it
Great choice. You'll see that uncertainty fade once the project begins.