TV is dead. Actually, the TV we knew as kids is dead. We no longer rush home to catch the latest episode of this or that. We've programmed it on our TiVo or DVR or better yet, we take out our tablet or smartphone and watch it wherever we happen to be at the time.
With all these video packets flying about, what is happening to our cable TV? Simple - Overcompression. Why? Because with more and more demand for high-speed access to the Internet, there's less and less bandwidth for MPEG-2 TV.
Now, you might ask, why don't the cable operators deliver all their programming over IP? IPTV has many advantages, and many MSOs (multiple systems operators, an acronym for the cable operators)have rebuilt their core networks to carry almost all their programming IP. It's the set-top-box that's the problem; over 65 million of them. These dinosaurs require video and audio in the form of MPEG-2 packets. Newer STBs, as they are called, can decode both MPEG-2 and MPEG-4 packets. It's the MPEG-4 technology that uses less bandwidth and delivers a better quality picture.
It's MPEG-4 and other innovative coder/decoders that let us watch high definition TV on our PCs, Smartphones, tablets, and web-enabled HDTVs. MPEG-2? Well, let's just say it's like last month's milk - turning sour and it's killing the cable business.
Now, if MPEG-4 (MPEG-4, Part 10, to be specific) is so wonderful, why aren't we seeing more of it? We are...in Europe, Asia, Brazil...places where the existing MPEG-2 networks are few and far between.
But, let's get back to the original issue - worsening video and audio quality on regular cable TV.
Some basics:
Before IP networks, TV channels were carried within a six megahertz bandwidth. On a scope, this bandwidth resembled a haystack with evenly sloping sides and a flat top. remember, one channel occupied one six-megahertz "Haystack."
As demand for more and more channels hit the MSOs, they pushed the upper range of the broadband spectrum out from 550MHz to 750MHz to 860MHz and now past 1GHz. But, the cost of expanding the upper range, somewhat like adding lanes to a highway, is very expensive.
Adding the Internet to the cable system was even more challenging. How were we supposed to carry ones and zeros? Well, we knew how to carry Ethernet over coaxial cable; we modulated an analog carrier. ones and zeros in...which were used to rapidly change the analog characteristics of the carrier and then, at the other end were decoded back into ones and zeros.
This haystack was an analog carrier. We figured out what characteristics we could change using a stream of ones and zeros and discovered that we could generate a pretty high data rate. One problem - bit errors; the signals were getting corrupted because of the poor quality of the cable system. Like a poorly maintained hotel, the windows were drafty, the roof leaked, and we were always blowing fuses. If we wanted to rent out our rooms for a high price, we needed a renovation. It kept a lot of us employed for a decade.
OK, so most of the cable operators have upgraded and fixed physical sytems and improved the culture of quality. Sure, there will be spots in any system that need rebuilding, but all-in-all, the MSOs run pretty tight ships.
In a frustrating turn of events, just as the cable industry got its act together, the wireless industry developed WiMax and LTE, over-the-air two-way, high-speed technologies that rival cable modem speeds. And, the Telcos rolled out Fiber to the Home (FTTH).
OK, OK...what about all this overcompression?
So, you're a cable operator. Your sources of capital have dried up. Your cities and states are regulating you like mad, requiring you to do things that use up valuable bandwidth for no additional revenue. Your customers are demanding more HDTV programming and faster Internet access speeds.
What gives in this scenario? Video and audio quality.
Remember the haystack; that 6MHz "channel?" We can modulate that carrier and decode a bit rate of 38.8Mbps. A good standard television program can be digitized so that a rate of about 3.8 Mbps will be enough to run the decoder and regenerate the video and audio. This means that we should be able to fit 10 programs into the space of one. Many operators stuff eight, but some stuff twelve programs into that 6MHz carrier.
So, "big deal" you might say. "Cool!" Not so cool.
MPEG-2 has a few quirks. It requires very precise timing so the packets can be reassembled in order. Funny thing about MPEG-2, some packets carry the information that tells the decoder when pixels on the screen are supposed to move. If we lose that "motion vector" packet, the pixels, in the form of 8X8 blocks, just stay on the screen while the rest of the screen changes.
MPEG-2 is sensitive to timing and to data corruption caused by noise. Artifacts caused by overcompression become more observable as the effective data rate falls below 3.8Mbps.
Is there a solution? Yes.
I'll cover that in my next article.
