Having same problem. The advertisements play and although the video says "playing now" nothing is playing there is just a black screen. I contacted Comcast on three occasions. They told me to add a different browser because my browser (Internet Explorer) is not compatible with Xfinity. I added Google Chrome and the videos still do not play. They told me at Comcast it may be a Norton or Constant Guard problem so they transferred me to Norton. The lady at Norton told me I need to get in touch with the computer manufacturer as there is a problem with my computer. All other videos from other websites, you tube, etc. play on my computer. The only one I have the problem with is Comcast Xfinity. I am tired of calling Comcast because they just keep passing the buck. I did not change anything on my computer and the videos played before...... so why won't they play now.
Wish someone had a fix for this problem because Comcast does not want to help.