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A comparison of bitrates between FiOS and Comcast reveals signals compressed up to 38%.  (Source: AV Science Forum)

Red Hot Chili Peppers live: crisp and clean on one side, a blocky mess on the other.  (Source: DViCE/AV Science Forum)
Comcast tries to fit three HDTV channels in the space of two

HDTV aficionados with Comcast service might be in for a rude awakening: the nation’s largest cable provider seems to have ratcheted up the compression on its cable HDTV signals.

A thread at AV Science Forum updated last Monday details what appears to be compression of up to 38%, allowing Comcast to deliver more HDTV channels per line while using the same amount of bandwidth. A side effect of this, however, means that HDTV’s pristine video is now jagged and muddy for Comcast customers, full of MPEG-style compression artifacts and stuttered movement:

For the most part, fine detail remains very good on static (non-moving) images with Comcast's added compression, but you do see reduced contrast, with more dithering artifacts (banding) between colors and objects. With some channels, it looks a bit like Comcast is taking a 24-bit image and reducing it to 18-20 bit. This tends to reduce the 'pop' effect in some images. The difference in 'pop' was quite noticeable on Food HD, despite the relatively small bitrate reduction.

The greatest differences are seen with movement. With slow movement on Comcast, the first thing you notice is added noise and a softer image, as fine detail is filtered from the picture signal. The greater the rate of movement, the more detail you lose and the more noise you see. With intense movement, you see more blocking and skipped frames. In VideoRedo, I noticed that a number of frames in the FiOS signal simply did not exist in the Comcast signal during motion intensive scenes. This may be responsible for the stutter and excessive motion blur seen with some video sequences on Comcast.

Still images comparing Verizon’s FiOS HDTV service with Comcast’s HDTV service, taken at the exact same time in the exact same broadcast, show Comcast’s images losing much of the legendary detail that HDTV is so well known for – in a screenshot  of the Red Hot Chili Peppers playing live in Milan, the Comcast image was almost completely stripped of all fine-grained detail; lead singer Anthony Kiedis’ textured wristband becomes flat and blocky, and the tattoo on his left arm made pixellated and blurry.

A request for comment was received by Comcast, but not replied to.

The purpose of Comcast’s increase in compression is unclear; however it would appear that the company is attempting to fit three HDTV video streams inside of one QAM (Quadrature Amplitude Modulation, Comcast’s DTV broadcast format) signal, as opposed to the previous two. In a bitrate comparison between each provider’s broadcast of the same show, the Verizon signal was recorded at 17.73 Mbps, while the Comcast signal recorded at 13.21 Mbps, a 34% reduction in size.

According to Ken Fowler, the A/V buff known as “bfdtv” at AV Science Forum, Comcast’s compression increase currently affects most customers that were not originally in Adelphia’s cable system, which Comcast purchased in 2005. Further, the increased compression only affects national networks like A&E or HBO; local TV signals are rebroadcast at whatever bitrate they were originally sent in.

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Another sad move....
By JasonMick on 4/1/2008 3:23:48 PM , Rating: 5
Why does Comcast seem so intent on ruining the customers experiences?? I always hate companies who think they can "pull a fast one" on what they think is an unwitting consumer market. It always ends badly for such companies. I'm sure Comcast will be seeing ramifications from this and the bittorrent debacle.

RE: Another sad move....
By sapiens74 on 4/1/2008 3:27:25 PM , Rating: 2
Comcast is making more friends everyday it seems.

I know our TimeWarner here broadcasts many channels over clear QAM and I can pickup with both my TV sets and my Vista Tuner, all of which are high quality. If it was compressed like that I would cancel my cable.

WHat really sucks is this is for people paying premium for the HD services....

RE: Another sad move....
By Chris Peredun on 4/1/2008 3:36:58 PM , Rating: 5
The truth is that those who look into the details - and are willing to record and compare bitrates - are the minority.

Comcast is catering to the majority of consumers, who will see "Comcast - Now with 50% more HD channels!" and sign right up.

RE: Another sad move....
By Mitch101 on 4/1/2008 3:45:51 PM , Rating: 2
Your absolutely right Chris.

Now I could see Direct TV or someone else using this against them just like the image demonstrates.

Yup can see the ads now. Not all HD sources are created equally.

I don't like comcast being so shady about stuff like this. In the end they should just sell upconverter cable boxes that take 480P signals and upconvert them to 1080i and claim HD while they are at it. Dont put it past them not to do that. Considering the video they are producing with poor compression and lower bit rates it and up converting might provide a better picture.

By therealnickdanger on 4/1/2008 4:27:16 PM , Rating: 3
Considering the video they are producing with poor compression and lower bit rates it and up converting might provide a better picture.

You may or may not be kidding, but it would likely be true!

RE: Another sad move....
By walk2k on 4/1/08, Rating: -1
RE: Another sad move....
By mindless1 on 4/1/2008 8:04:51 PM , Rating: 2
The truth is that anyone who would be recording and comparing bitrates already had a reason to suspect a problem, since anyone with reasonable eyesight can see the example picture above looks like crap. Maybe on Dad's old 13" SD set that wouldn't be noticable but on today's large digital sets it is clearly a terrible experience.

I agree though that most people will not realize this drawback until after having seen it for themselves, typically after they've signed up.

RE: Another sad move....
By JarredWalton on 4/1/2008 10:48:19 PM , Rating: 2
You know, I tuned in to several HD channels (on Comcast) and I see *nothing* even remotely like the artifacts shown above. Is it a localized thing? I mean, that MHD Chili Peppers image looks more like the signal is corrupted than just being recompressed. I've watched some 8Mbps broadcasts that still looked pretty good at 1080i, and a 15-25% typical bitrate reduction isn't all that large.

RE: Another sad move....
By djc208 on 4/1/2008 3:37:53 PM , Rating: 5
They have to make more room for the internet traffic now that they're not going to sensor bit torrents.

You didn't think they would actually improve their service by adding more bandwith did you?

Sad part is Comcast isn't unique in this, they're just the first to get caught.

RE: Another sad move....
By Heph on 4/1/2008 6:55:51 PM , Rating: 2
They have to make more room for the internet traffic now that they're not going to sensor bit torrents.

Actually this is not the case. Docsis 3.0 will be launching at the end of the year in most Comcast systems. This will allow channel bonding and enable Comcast customers to obtain faster Internet speeds on par with FIOS.

As of February of next year even though Comcast by law does not have to stop Analog broadcast on their closed system they will do so with the exception of basic cable (just local channels). So I am personally hoping this is just a stop gap to allowing them to broadcast more HDTV channels until some of the Analog spectrum can be reclaimed for digital services, but this is Comcast so you never know.

RE: Another sad move....
By mindless1 on 4/1/2008 8:09:52 PM , Rating: 2
The launch of Docsis 3 support does not mean they can just immediately switch everyone over.

Do you have a source for your claim Comcast will stop analog transmission in February? That would be surprising, as other cable companies are not currently planning to do so AFAIK (many have been asked by customers but are taking a position of waiting to announce any changes which seems like a delay beyond that timeframe considering all the customers who will need to switch equipment.

Further, many people overlook institutional customers. Schools, hospitals, nursing homes, etc - these people can't just switch on a whim, it is a massive undertaking which some simply won't be able to do at all.

RE: Another sad move....
By Heph on 4/1/2008 11:57:48 PM , Rating: 2
Let’s say I know they will be without giving to much info. Boston is already an all digital system. If you were to just plug any analog TV into a wall jack without a box you only get approximately 22 channels.

RE: Another sad move....
By theapparition on 4/2/2008 8:59:21 AM , Rating: 3
Boston is already an all digital system. If you were to just plug any analog TV into a wall jack without a box you only get approximately 22 channels.

Well, that wouldn't be all digital now, would it?

RE: Another sad move....
By djc208 on 4/2/2008 3:29:11 PM , Rating: 2
I keep hearing this, and I don't doubt it's truth but one thing bothers me about it, cable boxes.

If they took all the "normal" analog channels and made them clearQAM it wouldn't be so bad, but chances are they'll all be scrambled, so now I have to use their boxes at $6/month for each TV, oh and if I want to record from my HTPC that's more complexity/trouble/money, or I have to rent their crappy DVR for an additional $11/month.

One of the reasons I stuck with cable is because I can split it and connect it anywhere I want. They make it just like satalite and I'll probably just get a satalite.

RE: Another sad move....
By NaughtyGeek on 4/1/2008 3:44:13 PM , Rating: 2
Well, I've been toying with switching to FIOS for quite some time and this will likely be the final straw. I actually was ready to move once but they upped my package for the same price but if they're going to give me DirecTVs HDLite BS, I'm done with them.

RE: Another sad move....
By FITCamaro on 4/1/2008 4:09:28 PM , Rating: 5
I think you're nuts if you've got the option to use FiOS and you're not. They couldn't sign me up quick enough if I had the option.

RE: Another sad move....
By theapparition on 4/2/2008 9:24:18 AM , Rating: 3
As a FIOS customer myself, and former Comcast subscriber, I can clearly say that they are Superior to Comcast. So much so, that when switching services, usually they give the "AOL" hard pressed sell to keep you as a customer, but when I told them I was going to FIOS, she just said "I understand".

Now, while I'm totally enamored with the FIOS service, here's the downside. Verizon is in it's infancy as far as TV is concerned, specifically service. They don't have their act together. I've had some issues.
When initially installed, they didn't turn on HBO and some of the cable boxes were the wrong type (more on this below). I wanted to swap boxes and get HBO turned on. After being on the phone for hours with multiple disconnects (wait, isn't Verizon a phone company?) they finally told me (compressing very long story) that they'd have to turn on HBO (take a few days??? WTF, comcast does it in a few minutes), and when that was complete, I could then open up another service record for my address to swap the box.

As for swapping the hardware, they do have local stores which I opted to do rather than pay for someone to come out and inconvenience my wife. I thought the exchange would be as easy as walking into the Comcast store. Far from it. I walk in, told them I wanted to swap hardware. He asked for a service number (mind you the phone rep told me to go to the store, without mention of a service number). I had to pick up a verizon phone in the lobby, call verizon, wait an hour, then get a service number so the guy can swap my box. Just not organized at all.

A huge plus with FIOS is that it offers a multi-room DVR, something that Comcast severely lacks. Here's the problem with the multi-room DVR won't work with HD satellite boxes. I have 6 HDTV's in the house, with a 60" TV in the bedroom. Obviously, I wanted HD on that TV. But the HD box won't talk to the HD DVR. You have to have a standard box to get that functionality. So I had to swap a few HD boxes for standard ones to get that to work (wife's insistence since she likes to watch a lot of DVR TV in bed). This is supposed to be upgraded at some time in the future, but for now it really sucks that I can't have the best of both worlds.
FIOS uses Motorola hardware, which plain sucks. I came from Comcast's Scientific Atlanta boxes which were much better (Comcast uses Motorola in other areas).
I also had an issue recently where the multi-room DVR got "out-of-sync". The shows stored on the main DVR did not match up to the available stored shows on the satellite boxes. I had to reboot the network (Verizon's tech support) and everything got back into sync, but I also lost several shows on the main DVR. Pift, gone. I was not happy.

Still, they are getting better, but do have some growing pains.

Internet and phone service has been exceptional. It still blows me away when i start a download and it comes in at 2.5MB/s sustained. Vista SP1 took just a few minutes for the entire distribution! Gotta love that.

RE: Another sad move....
By winterspan on 4/1/2008 9:08:34 PM , Rating: 2
For once, I actually agree 100% with FITCamaro. You'd be bat-shit crazy to keep service with ANY cable or satellite provider if you have access to FIOS. Because of the fiber to your door, FIOS will always have a much better capacity for high bit-rate, minimal compression HDTV, more channels, more VOD options, etc. And the best part of all is the availability of ultra highspeed net access.

Don't listen to the misinformation from 'Cable' about DOCSIS 3.0. Bottom line is that the coaxial cable network is a shared medium, so if you live in a dense area with many subscribers, your average throughput will be nowhere near the stated "maximum" speed. This will be more prevalent now that average users are starting to use a lot more bandwidth than in the past. Joe sixpack is now streaming high-bitrate and even HD video from websites like, BBC, Hulu, Netflix, iTunes, etc. Others are downloading large video podcasts or DVD rips and lossless music files from Bittorrent and P2P software at all hours of the day. Beyond just the home computer, you are also seeing video game consoles and standalone STBs offering movie rental downloads and online gaming.
With all of this traffic, it will be hard for cable to compete with Fiber-to-the-home FIOS service, even with DOCSIS 3.0 and other network enhancements.

RE: Another sad move....
By Cullinaire on 4/2/2008 1:46:09 AM , Rating: 4
"For once, I agree with FITCamaro" -multiple authors

should be one of the rotating quotes on the bottom of the page.

RE: Another sad move....
By therealnickdanger on 4/1/2008 3:44:32 PM , Rating: 3
I've used Comcast for a long time now and I can safely say that I *hate* it. I don't use that word often. Unfortunately, they are the ONLY game in town. FIOS is effectively blocked from competing in this area and satellite/DSL can't compete with the Internet speeds Comcast offers. I had some really good experiences with Time Warner before Comcast took over their portion...

RE: Another sad move....
By MADAOO7 on 4/2/2008 12:36:35 AM , Rating: 2
Just to clarify, Comcast isn't what blocks FIOS, its whatever phone service you have in the area. FIOS runs on verizon's "phone" network, which is how they get around the gov't regulated monopoly Comcast has in your area. The fiber optic lines that FIOS runs on replaced the prior copper lines that Verizon used for voice services.

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