I use a Mac mini as a media computer plugged in to my TV. I use it to listen to music & watch TV shows & movies stored on my Synology NAS. When I want to control the mini, I use Screen Sharing to connect from my MacBook Pro. I finally upgraded the mini from Lion to Mountain Lion, & everything went swimmingly. I thought.
Last night I put in a DVD, which automatically opened DVD Player, & then connected to the mini via Screen Sharing. Immediately, the window showing the DVD turned into a gray & white checkerboard pattern. I tried a different DVD. Same thing. What the hell?
After poking around on Google, I found the answer, & it’s craptastic. A user named toastador on Apple Discussions explained it well:
After sitting on the line with Apple support and doing some troubleshooting, I finally figured out some additional things that might help out. With the update to Mountain Lion, Apple seems to have enabled a feature that causes the grey and white checkerboard to appear in any of Apple’s video playing software if there is any type of streaming or other connection active to the subject computer. For example, prior to the Mountain Lion update, I had my Mac Mini connected to my television. To make things easier on me, I would use the Back to My Mac feature to do screen sharing to navigate through the Mac Mini. However, after the Mountain Lion update, I would get the gray and white checkerboard pattern in DVD player and in iTunes when trying to play videos (whether or not they were DRM protected). But if I didn’t use screen sharing but rather tried to play the videos on the Mac Mini using the typical bluetooth keyboard/mouse interface, then the videos would play perfectly. 0,0,1440,900
This same issue arises with Airplay Mirroring. When you try to mirror your desktop/laptop computer to the TV through the Apple TV, your desktop/laptop computer senses that you are doing a type of screen sharing. As such, whenever you try to play anything through the Apple software (i.e. DVD player, iTunes, etc.), the result is that you get the grey and white checkerboard screen.
At this time, there doesn’t seem to be any type of workaround for this except to use third-party software when you mirror, as has been noted by other posters on this thread. It doesn’t matter whether you are trying to play DRM protected material or not, the computer you are trying to mirror will sense the connection to another device and will automatically checkerboard all video you attempt to play.