Quicktime symbol with a question mark in it

I have the latest version of OS X Yosemite 10.01.2. On some websites some of the videos I would like to view come up as a quicktime symbol with a question mark in the middle of it. I cannot figure out why I am not able to view the video. I see that there have been several other people having this problem. I just cannot find a solution that is current. can anyone help me out?