8m or so is the limit for HDMI passive cables being 100% reliable. If you want to go 15-30m--- using a video source from another part of your house, or to driv

8m or so is the limit for HDMI passive cables being 100% reliable. If you want to go 15-30m--- using a video source from another part of your house, or to drive a projector in the middle of a classroom--- and you buy an "active cable", odds are it's fiber optic inside. If you want to go hundreds of meters away, you'll get a purpose-built box that uses your own optical cables instead of a cable that hides the optical transceivers inside.