Black bar closing effect

I'm so new! Excuse me if my topic is duplicated. I've searched the topic and couldn't find, at least I thought. I'm trying to create the black bar closing effect. Where the screen closes bit by bit ( not fading down). Not closing all the way but like in music videos, come down a little and the back up. Can someone give me step by step instructions or a link to detailed instructions?
Thanks for this!

Can you link to an example?

a few suggestions how to accomplish that are in this tread:
discussions.apple.com/thread/5288166?start=0&tstart=0

If that's it, just keyframe Crop parameters.

Step by Step

1. Select your clip in the timeline.
2. Go over to the inspector and scroll down to the "Crop" section.
3. The "Type" should be set to "Trim".
4. Go down to the "Top" and "Bottom" parameters and set a Keyframe for each.
5. Use your mouse or the arrow keys to move the playhead to the point where you want the the effect to end.
6. Assuming that you are editing 1080 footage, change the "Top" perimeter to 540 and the "Bottom" to 540 as well which should have both ends meet in the middle.

WahBam!! There ya go! Hope this helps!