Samsung 7000 series 55" 3-D LED screen blacks out
I'm sorry to hear that you're having this issue with your TV and Netflix.
For Netflix, it may be how the rebuffering occurs. With the newer firmware updates, if the bandwidth changes speeds (either Internet or your home network), the TV will automatically readjust the picture and "switch the picture" based on available bandwidth.
For Blu-Ray, this is a little more of an oddity. I might suggest seeing if a different resolution to the TV helps, or if swapping out the cable changes the frequency. Some "black out" would be like static on analog sets. I can't explain every instance where it might occur, but if it's happening frequently, then it may require further investigation.