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What’s the Point of HDMI?

Al Griffin  |  Jan 13, 2016

Got a tech question for Sound & Vision? Email us at AskSandV@gmail.com

Q In a picture accompanying S&V’s recent article on VIZIO’s Reference UHDTV, I noticed a coaxial cable input on the back panel next to the HDMI connections.  This made me wonder why coaxial cable is used to convey over-the-air and cable HD signals, but HDMI connections are used to carry them the last six feet to our screens. Is the issue copy protection in the HDMI cable?  Or is it about compression/decompression? —Ben Hurwitz / Greensboro, NC

A With HDMI, it’s about copy protection. But let’s first address that coax jack. The coaxial cable input on a TV’s back panel is provided to connect an antenna designed to pull in digital TV broadcasts. A tuner inside the TV then demodulates the signal, stripping audio/video from the radio frequency carrier. Next, the MPEG-compressed A/V stream is decoded so that your TV can display it.

With digital cable, the process is similar, except a different modulation method is used to convey signals over the cable TV system’s wired network to your cable box.

Once HD signals are decoded by your cable, satellite, or other-type receiver, the uncompressed video and audio gets routed to an HDMI output. Those signals are then encrypted using a DRM (Digital Rights Management) scheme called HDCP (High-bandwidth Digital Content Protection). For the source device to pass the signals, a “handshake” must occur with he receiving device. This process creates a secure digital connection that prevents any content from being copied.

So yes, the main function of HDMI is to protect high-resolution digital content from being copied as it’s transmitted from the source device to a display. Movie studios demanded it, consumer electronics manufacturers stepped up to supply it, and that’s why HDMI is the predominant connector type on today’s A/V gear.

COMMENTS
hbomb7's picture
Submitted by hbomb7 on January 15, 2016 - 9:32am

I still think HDMI sucks because you can't but both video and audio into one cable - it never works!!!! The handshake problems still rears it's ugly head even as of today.

mikem's picture
Submitted by mikem on January 15, 2016 - 9:30pm

Leave it to Hollywood paranoia (think Disney) and you end up with hdmi that has more drawbacks than a screen door on a submarine. The whole "handshake" crap is bad enough but the nitwits who designed and engineered the terminal connections should be sent to a distant planet never to see the light of day. I actually would like to know the technological decision to create this abysmal failure.

Traveler's picture
Submitted by Traveler on January 18, 2016 - 10:40am

I don't understand why everything isn't connected (with security if it's that big a deal) with one fiber. Fiber can carry way more data than all the devices in a a/v system generate with zero data loss, and it requires a very small connector.

pgbinder's picture
Submitted by pgbinder on January 18, 2016 - 1:11pm

Anyone with cable TV is pretty much forced to use HDMI interface now that most cable systems have gone "digital". That fancy remote that came with your expensive TV is relegated to being a doorstop. My cable supplier (Cox) no longer passes (down-res) Analog, or even Digital, TV channels. You must now "rent" (for $2 per month) a Mini-box (with Mini-Remote), that has only Channel 3 RF or HDMI outputs, for every TV. So, HDMI is for just about everything!

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