WTF! Why Can’t I Play My Video So you tried to watch an mp4 video in Windows 10 and it threw an error at you that “To play this video, you need a new codec, HEVC Video Extensions and they want you to pay $0.99 for it. If you are like me, you are wondering what the heck is the HEVC Video Extensions and why all of a sudden do I need it to watch an mp4.