Macbook Retina 15" camera - hardware, firmware or software issue?
The green LED is hardwired to the camera. If the green light is on, the camera is on. If the green light is off, the camera is off. So, I believe your camera is turning on and off, on and off, on and off…

There are a couple other things you can try:


Try a different user account: if you have another user account on your MacBook, log in to it and try to use the camera. If not, first create a new user account via the System Preferences. If the camera works in the alternate user account, then you can safely say that something with your account's settings aren't quite right.
Determine whether your MacBook properly recognizes the camera: Check System Profiler (in the Utilities folder, inside the Applications folder). Under the USB header, check to see if the iSight camera is detected.


(I found these troubleshooting steps on Apple's Support Website:
How to Troubleshoot iSight.)

If these don't help, then it's probably a hardware issue: you'll need to take your MacBook to a local Apple Store Genius Bar (or other authorized Apple Service Provider) for further help.