I just now downloaded YTD Video Downloader from Cnet. The iSight indicator is not flickering on my Mac Pro's Cinema Display. I also tried my 13" Mac Pro with no flickering there either.
darkduo009 wrote: ...Is the computer broken? ...
Not if this is the only problem you are experiencing. Here are some things you can consider that may help you:
Be sure you don't have some camera enabled apps running. The check should include Login Items.
Try turning your rMBP off for five minutes. Then boot again and see if the problem continues with no apps running and no ancillary hardware connected.
If it does, use > Software Update... to be sure your Mac's Apple software is up to date.
Check your Mac's > System Preferences... > Sharing to be sure you aren't Sharing unknowingly.
If the problem continues, Reinstall OS X Mavericks and then check again for the problem.
If all else fails and you do not want to take your Apple to the Store for service, consider Apple Authorized Service Provider or online Apple help.