Current Events In Advanced Video Compression4/27/2007 8:00 PM Eastern
It was way back in the summer of 2004 when this column last checked in on advanced video compression. Back then, it “wasn’t yet ready for primetime.” For cable and satellite operators, doing it meant deploying a new line of digital boxes.
Generally speaking, that’s a deal-breaker: The deployed base of boxes can’t do it? Good luck. Thanks for playing.
And here we are, three years later — and two weeks after the show floor of the National Association of Broadcasters Convention in Las Vegas teemed with makers of advanced video encoders. From the looks of things, a lot of innovation dollars are pouring into the making of better video squishers.
Why is that? One big driver is AT&T, which is building its residential video service to run over DSL (digital subscriber line), which runs over existing phone wires. DSL pipes aren’t as roomy as hybrid fiber-coax (HFC) or fiber-to-the-home pipes.
To get video stuff through DSL — HDTV, especially — it needs serious squeeze. More than what’s available now, known as MPEG-2.
PROGRAMMERS AND MPEG-4
At the other end of this tale are the program networks. Say you live in that world, and you want to supply your content to AT&T. Then you learn that AT&T wants your stuff compressed at a much greater extent than you currently offer.
If that’s you, then someone in your company is probably looking at advanced video encoders — maybe for your company, maybe to see what could happen if your pictures pinch through someone else’s compressors.
At the same time, you’re probably wondering if this means you have to send your stuff two ways — the existing way (MPEG-2), and the new way, MPEG-4 (which also goes by an assortment of reasonably synonymous acronyms: AVC, VC-1, H.264).
“But wait!” say the encoder suppliers. There’s a sexy economic angle here. Satellite transponders are expensive — upwards of $125,000 per month, each. What if you could send everything up in MPEG-4, then convert it back to MPEG-2 on the ground, if you need to? And if you don’t, just send it along as is.
The meat of the pitch: Mash your merchandise down twice as much, before it goes up into space. Save serious cash on satellite costs. (And you need encoders to do it.)
For the technical people who oversee the making of video content, though, such ideas tend to elicit this loud and constant refrain: “Be careful with the encoding. That’s my baby you’re squishing.” Primarily, they’re concerned about the amount of digital man-handling that will happen to their products, en route to all those discerning eyeballs.
Let’s take it from the perspective of a digitized movie. It starts life as a digital video tape — which means it’s already been compressed once, from the studio source feed, to fit the tape. Next, it gets compressed in the MPEG-2 format, for transport.
Let’s say it then goes to an aggregator, where it is “up-rated” back to roughly the size it was when it was on tape, then re-coded into the MPEG-4 format. That’s four manipulations.
In both cases — changing something encoded in MPEG-4 into an MPEG-2 format, and changing something encoded in MPEG-2 to an MPEG-4 format — you need encoders.
And then there’s that pesky box issue. The stark realities of legacy gear apply here: Today’s deployed armada of digital boxes just doesn’t come with chips that can decode MPEG-4 streams.
Ask around, though, and you’ll hear more and more operators say the boxes they deploy after July of this year will contain chips that can decode both MPEG-2 and MPEG-4 pictures.
Some cable technologists say MPEG-4 will enter the scene through the door marked HD. That takes care of the box take-up issue: Customers who sign up for HD, after July, theoretically get the box with the dual decoder chip.
Then there’s the issue of sending video in yet another way, which requires bandwidth. Less bandwidth, sure, but bandwidth.
To that, some on the cable tech side are mulling whether they could send the MPEG-4 material through the video switches they’re gearing up to install. Switching logic stipulates that only what is requested, is sent. If what’s requested is an HD stream, pluck it off in MPEG-4, then send it through the switch.
That way, advanced compression phases in, over time.
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