Is your Comcast HD quality up to snuff?

[PaulGo]

From this interview Cox will be doing the same thing - three HD channels per QAM.

http://forum.cabletv.com/cox-communi...html#post14784 (Cox Decreasing HD Bitrate)

[PaulGo]

Comcast, others degrade HD video quality to pack in more channels

Mon Apr 7, 2008 5:22PM EDT

High-definition television provides a crystal clear viewing experience, free from artifacts and with noticeably better quality than standard-definition television... right? Not so fast. Turns out Comcast and other providers of so-called high-def TV are intentionally compressing the video stream on many of their channels, sometimes by as much as 38 percent, degrading image quality along the way. Why? Supposedly, it frees up bandwidth so the operators can pack in even more channels.

The news is the result of independent research from a user at AVS Forums, probably the best-known meeting ground for audio and video enthusiasts. Here, that user provides a wealth of examples and empirical data outlining the issue, complete with screenshots of what channels look like with standard compression and with Comcast's extra squeeze. Some of the channels don't look much different, but a few examples are particularly egregious, such as the 34.2 percent added compression applied to MHD, seen above in a "before and after" shot. (Note that this level of pixelization will be less apparent in a moving image than a still frame, bit some of the examples are so horrible they'd be obvious to even a casual passerby.) Some commenters have noted that the compression is so bad they thought something was wrong with their equipment.

Comcast isn't the only one pulling these stunts. DirecTV has been sued over a similar issue in the past, and DISH has also engaged in such "HD Lite" tactics as well, namely by dropping the overall resolution of its broadcasts to save on bandwidth. In fact, DirecTV actually sued Comcast when Comcast tried to call out DirecTV's lower-resolution HD in its advertisements. That suit was settled late last year. Now maybe it's time for DirecTV to launch an ad campaign of its own...

Comcast has yet to issue a response regarding this issue.

Comcast, others degrade HD video quality to pack in more channels : Christopher Null : Yahoo! Tech

[cablewithaview]

One thing I meant to clear up when discussing QPSK to 8PSK, this mainly deals with satellite transmission of the feeds. While Comcast uses a megastream (aka megapipe for c band 4dtv users) the high symbol rate using a combined forward correction error (fec) allows for more data to be delivered but many has questioned Comcast method on the satellite side concerning delivery to the head end. I believe as for the satellite transmission side of it, Comcast will have to change the delivery of the feeds from QPSK to 8PSK to be able to deliver a quality product to the head end.

[PaulGo]

HD enthusiasts crying foul over cable TV's crunched signals

By CHRIS WILLIAMS 4/20/2008

MINNEAPOLIS (AP) — In Brent Swanson's basement home theater, there should be nothing drab about "Battlestar Galactica." He's got a high-end projector that beams the picture onto a wall painted like a silver screen, and speakers loom in the corners, flanking two big subwoofers.

Yet when he tuned in Sci Fi HD for a recent episode filmed in high definition, the image was soft and the darkest parts broke up into large blocks with no definition. Explosions, he said, were just dull.

"It kind of looked like they took the standard definition and just blew it up," said Swanson, a 33-year-old graphic designer and videographer who subscribes to Comcast Corp.'s TV service. "I couldn't really tell if what I was seeing was really better than what I saw on regular television."

As cable TV companies pack ever more HD channels into limited bandwidth, some owners of pricey plasma, projector and LCD TVs are complaining that they're not getting the high-def quality they paid for. They blame the increased signal compression being used to squeeze three digital HD signals into the bandwidth of one analog station.

The problem is viewers want more HD channels at a time when many cable and satellite providers are at the limits of their capacity, said Jim Willcox, a technology editor for Consumer Reports magazine.

"They have to figure out a way to deliver more HD content through their distribution networks," he said.

Compressing the signal is cheaper than costly infrastructure upgrades to increase capacity. Satellite TV providers — including DirecTV Group Inc. and Dish Network Corp. — also have the option of launching satellites to boost the number of HD channels on their systems.

While information is nearly always lost when signals are compressed and then uncompressed, the process can theoretically be made unnoticeable to eyes and ears — and Comcast says it should be.

But some viewers say they can see it. Willcox said complaints about compression have been showing up on Web forums, including the AV Science Forum, a site for serious audio visual enthusiasts.

"It's not exclusively Comcast, although Comcast, being the largest cable provider, is probably the largest target," he said.

Derek Harrar, a Comcast senior vice president in charge of video, said the company recently began using new technology on some channels to compress three HD channels into the bandwidth of one analog station. Other channels continue to get the previous 2-to-1 compression.

In a posting on the AV Science Forum, Ken Fowler of Arlington, Va., compared Comcast signals with those on Verizon Communications Inc.'s all-fiber-optic network, which doesn't have the same capacity limitations. Fowler found the higher-compressed HD stations, including Sci Fi, Animal Planet, the Discovery Channel, the Food Network and A&E, fared particularly poorly.

He analyzed the signals by recording them on a digital recorder, then transferring them to a personal computer for analysis. He found there was much less data, measured in bit rates, flowing to some channels than others.

For example, Discovery's bit rate was 14.16 megabits per second on Verizon's FiOS system but only 10.43 Mbps on Comcast; A&E HD was 18.66 Mbps on FiOS compared with 14.48 Mbps on Comcast. The FiOS system didn't offer Sci Fi HD, which Fowler's testing showed at 12.59 Mbps on Comcast.

He found the signals from the major networks and ESPN weren't getting the increased compression.

In an interview, Fowler said he reran his analysis about two weeks ago and found "basically the same thing."

Philadelphia-based Comcast wouldn't identify specific signals that are 3-to-1 compressed, and a Sci Fi channel spokeswoman referred questions back to Comcast.

Harrar said the company works to make sure any new compression technology is invisible to consumers, but Comcast is "constantly monitoring our network and making adjustments" for best picture quality. The company has been rolling out the new compression technology at different times around the country.

In fact, postings on the AV Science Forum from early April suggest the Comcast network has improved in some places.

And there are other reasons a high-definition picture can appear subpar: The source image might not have been recorded in HD, or the television's settings, the viewing angle and even the ambient lighting in the room could be the cause.

New York-based Time Warner Cable Inc. has avoided many of the criticisms aimed at Comcast, although the companies are technologically similar and face the same capacity limits.

Time Warner spokesman Alex Dudley attributed it to his company's testing procedures. He said that before Time Warner rolls out new technology that may affect image quality, it sets up two identical televisions in a lab, one with the old signal and one with the new. Technicians make adjustments until the pictures can't be told apart.

"The testers are our engineers who we call 'golden eyes,' who have a proven track record of picking up subtle differences in picture quality," he said.

Verizon's FiOS doesn't compress the signal once it receives it, and Willcox said it's considered the picture quality "benchmark." However, Verizon said the system is growing but is now available only in parts of 17 states and has just over a million subscribers — compared with more than 24 million for Comcast.

He said two possible solutions are on the horizon, an improved version of compression, called MPEG-4, and something called "switched digital video."

Comcast and Time Warner Cable have introduced switched video on a trial basis across their networks. In concept, it's like on-demand videos. The company sends only the channels the viewer is watching, instead of all the channels at once.

But switched video has its own issues, including possible slower channel switching times and compatibility problems with digital video recorders.

Willcox said cable providers can't afford to ignore quality complaints. Many customers are already picky about quality after paying $800 to $3,500 for an average-size, HD-ready LCD television.

Swanson, the "Battlestar Galactica" fan, is sticking with Comcast for now.

"It hasn't gotten bad enough for me to consider changing," he said.

The Associated Press: HD enthusiasts crying foul over cable TV's crunched signals

[PaulGo]

This link includes a video done by KPIX TV.

cbs5.com - HDTV Fans Cry Foul Over Cable's Crunched Signals

[cablewithaview]

To deliver more HDTV channels, cable and satellite services are resorting to new compression algorithms. But some viewers fear that quality is suffering as a result.
Louis Chunovic, PC World

Do your HDTV programs look as good as they should? If not, you may be seeing the results of overcompression. A growing number of viewers and experts are claiming that increased use of compression--technology that downsizes huge high-definition video streams for eventual reconstitution on your screen--is responsible for a drop in quality.

Such charges--aimed mostly at the two biggest cable providers, Comcast and Time Warner--have been echoing around the blogosphere in the wake of reports about new compression algorithms. Contributing to the debate: An AVS Forum member's tests showed that at least ten HD networks were more compressed on Comcast than on Verizon's fiber-optic-cable-based FiOS service.

While service providers insist that quality remains a high priority, some experts say competition has made channel quantity, not quality, the top priority.

It's no secret that most digital TV is compressed and decompressed--in some cases several times--not just by cable or satellite services and over-the-air broadcasters but also by the video cameras that create the programs and the network satellite systems that deliver them to distributors. Compression happens, too, in trucks, control rooms, cable headends, and other waystations along the signal's path to your screen. The telltale signs of overcompression include tiling, little colored blocks, and "mosquito noise," which looks like flaring fireflies. The crispness of the picture can suffer, too.
Quantity vs. Quality

Compressing huge HDTV video streams, however, allows carriers to deliver more of them. "Everyone's really fighting the same issue--limited bandwidth--[but] their offerings are more attractive if they give more channels," says Peter Symes, director of standards and engineering for the Society of Motion Picture and Television Engineers. "There are big arguments in the broadcasting community about whether you should use virtually the whole of the 19.2 megabits you get for a single HD channel to deliver really good HD, or whether by using other standards or more compression you can get away with a high-definition [signal] and one or two standard-definition [signals] or maybe sell part of it for data services."

Currently, quality is "minor to a vast majority of the viewing public, because the vast majority...doesn't have very big TV screens," HDTV consultant Peter Putman notes.

But those viewers who do are starting to notice, including AVS Forum member Ken Fowler of Arlington, Virginia, a self-described audio-video enthusiast who posted the results of his Comcast-FiOS comparison.

Fowler had dropped Comcast for FiOS, but renewed his Comcast service (while retaining FiOS) in order to get Washington Nationals games in HD, and he began noticing quality differences between the two services. Some of the Comcast channels, he says, "didn't have the same pop, the same level of contrast, and there was a lot more blurring during movement."

So Fowler began recording the same shows on both FiOS and Comcast with his TiVo; he then downloaded the files to a computer and calculated the bitrates based on file size. The differences ran from just 0.7 percent more compression on Comcast for HBO HD to a whopping 38.5 percent for Discovery HD Theater.


PC World - Is HDTV Compression Damaging Picture Quality?

[PaulGo]

Although this article is a bit old and does not deal directly with Comcast it explains the various methods cable operators cable operators can use to reduce the bandwidth of a signal so they can squeeze in more channels.

DTV over digital cable: Reaching a larger audience

DTV over digital cable: Reaching a larger audience