Another common way to watch an HD movie is streaming the movie via Netflix or a similar service. This is a highly compressed, and likely a 720p (1,280x720-pixel) signal. Compression is a way to squeeze HD into lower data rates, making them easier to transmit. The side effect is a softer, noisier image. Generally it's still better than DVD, though.


HD quality Not all HD signals are the same. Just as an HD TV isn't necessarily showing HD video, just because something is called HD doesn't mean it is actually true HD-quality. I've mocked up some images below to demonstrate what three sources of different quality can look like. Remember, all three are 1,920x1,080 "Full HD 1080p," but as you can see, their quality is visibly different.


The job of the cable in a digital signal circuit is clear enough: maintain the specified impedance, as tightly as possible. Video cable is designed for 75 ohm characteristic impedance, and analog video cables to that spec have been in production for many decades; but tolerances, in a world of analog composite video running at a bandwidth of a few megahertz, were not as tight as modern digital video signals require. The advent of high-bitrate digital video required cables with exceptionally tight impedance tolerance--that is, as little deviation from 75 ohms as possible. Solving this problem required cable manufacturers to address every aspect of coaxial cable design, from drawing wire to more consistent diameter to making the microscopic bubble size in polyethylene foam more consistent, to figuring out how to structure that foam to prevent the dielectric from distorting excessively when cables are flexed. The result is the modern "precision video cable," with specified impedance tolerance of +/- 1.5 ohms, and in-practice tolerance tighter still.