One of the Xbox One’s interesting selling points is its HDMI pass-through. Microsoft’s next-gen console will have two ports that will allow any HDMI compatible device to be attached to the Xbox One and share a split screen with the video game console. Any HDMI compatible device includes the PS4.
It’s a bit funny that Microsoft’s Xbox One will be compatible with its biggest console rival but connecting the two together may not be worth it. While Microsoft has confirmed that the PS4 can be connected to the Xbox One HDMI port, they've further added that it won’t work very well. The discouragement of plugging in a PS4 goes for other consoles as well.
Any interactive sort of entertainment is going to experience lag from the HDMI pass-through. So playing a PS4 game side by side an Xbox One feature will probably be a less than optimal experience. Microsoft has explained that the HDMI port feature was designed with ‘passive viewing’ in mind, such as watching movies. A little bit of lag however, isn't going to stop many a gamer from hooking up Xbox 360’s and PS4’s to their new Xbox One just to try it out. Most users however will have it connected to a Blu-ray player or similar device.