The CinemaNow video quality is directly affected by your internet connection speed.
Currently, there are 4 quality levels possible for each video. You can see the quality level bars you are receiving during video playback in the right top corner of the TV screen. If all four quality bars are filled, you are receiving the highest picture quality currently available. If your quality bars are constantly moving back and forth and causing your video playback to lose quality, try shutting down other computers or devices connected to the Internet so your device has the maximum Internet speed available to it.