Comcast Trades Quality for Quantity with HDTV Offerings

eHDMI · 04-02-2008, 07:06 AM

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.

Source

Loves2Watch · 04-02-2008, 10:16 AM

As they have been doing in my market all along. Comcast here is the absolute worst HD provider.

Emil · 04-02-2008, 01:54 PM

The exact reason why I'm having Directv installed this Friday.

Scottnot · 04-02-2008, 02:32 PM

Quote:

Originally Posted by Emil

The exact reason why I'm having Directv installed this Friday.

Make sure that you have done your research.
I believe that DirecTV uses even heavier compression than comcast.

Emil · 04-02-2008, 03:16 PM

Quote:

Originally Posted by Scottnot

Make sure that you have done your research.
I believe that DirecTV uses even heavier compression than comcast.

I did,
They used to but now they have new satellites and are using mpeg4.

BobY · 04-02-2008, 03:20 PM

Technically MPEG4 is heavier compression--but it is a more efficient codec so it can still look good.

Chris Gerhard · 04-02-2008, 04:59 PM

I have both Comcast and DirecTV for the time being here in Little Rock and I would say Comcast picture quality for the few common HD channels is slightly better but the channel selection for DirecTV is far better. Both services compress too heavily and I hope DirecTV can improve. DirecTV has MGM HD and HDNet Movies and those two channels provide more of interest than all the Comcast offerings combined for me.

Chris

Type A · 04-02-2008, 05:19 PM

Its only a matter of time before providers start to claim the least compression...guess comcast wont be one of em eh?

Emil · 04-02-2008, 06:21 PM

I'm resigning myself to the fact for the best quailty picture I'll need to go OTA (which I have as a backup) and BluRay. I just had a feeling that the quality of Comcast was going to slip and Directv is going to be better.

I'll also be able to compare the two on Friday since I'll have both for a few days till I cancel Comcast.

mdustin · 04-03-2008, 02:53 PM

I E-mailed the comcast Tech Support section with a specific question regarding your accusation. they could be lying, but immediately responded that they're not doing that. I'm in Sacramento....could it be our area is not affected?

Emil · 04-03-2008, 03:35 PM

Quote:

Originally Posted by mdustin

I E-mailed the comcast Tech Support section with a specific question regarding your accusation. they could be lying, but immediately responded that they're not doing that. I'm in Sacramento....could it be our area is not affected?

Last year I asked DirecTv if they were doing HD Lite, they denied it.

Who do you believe? I sure don't know.

oblioman · 04-03-2008, 07:23 PM

Quote:

Originally Posted by Emil

I'm resigning myself to the fact for the best quailty picture I'll need to go OTA (which I have as a backup) and BluRay. I just had a feeling that the quality of Comcast was going to slip and Directv is going to be better.

I'll also be able to compare the two on Friday since I'll have both for a few days till I cancel Comcast.

Comcast quality slip?

How could that happen?

camper9 · 08-28-2009, 05:04 PM

Has Comcast's HD quality improved since this thread was first started? Or is Comcast still sacrificing HD quality in order to have more "HD" channels?

firsTraveler · 08-30-2009, 05:37 PM

Comcast has quality HD? Where? Quantity? Again where?

Neither is here.

jstrazz · 08-30-2009, 07:09 PM

Very happy with Dish Network and OTA.

04-02-2008, 07:06 AM	#1
eHDMI Vizio 37 LCD Join Date: Mar 2006 Posts: 1,647	Comcast Trades Quality for Quantity with HDTV Offerings 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. Source __________________ Discount HDTV Accessories HDFury

04-02-2008, 10:16 AM	#2
Loves2Watch SPAM Police Join Date: Aug 2007 Location: AZ, NM, TX, MX Posts: 13,928	As they have been doing in my market all along. Comcast here is the absolute worst HD provider. __________________ Theater 1 - Panasonic TH-85PF12U Plasma TV, 6 Conrad Johnson LP275M Amps, Anthem Statement D-2 Pre/Pro, 6 Thiel SCS4 Speakers, 2 REL T-1 Subs, Infinity Interlude 120S Sub, Simaudio MOON Orbiter Universal Disc Player, ELP Laser Turntable, 2 Dish Network ViP 622 DVR's, Oppo BDP-83 Blu-ray Player, Onkyo DV-HD805 HD DVD Player. Friends don't let friends buy Korean brand TV's.

04-02-2008, 01:54 PM	#3
Emil High Definition is the definition of life. Join Date: Oct 2004 Location: Barrington, Il. Age: 57 Posts: 1,224	The exact reason why I'm having Directv installed this Friday. __________________ 60A2000 SXRD Klipsch PS3 DirecTV

04-02-2008, 05:19 PM	#8
Type A 1080 Optical Supporter Join Date: Aug 2006 Location: Panama City, Fl Age: 38 Posts: 2,724	Its only a matter of time before providers start to claim the least compression...guess comcast wont be one of em eh? __________________ Mitsubishi HC3000U HD projector Dual Optoma 106" screens Harman Kardon AVR-7000 receiver Bose 901 VI, 301 IV, VCS 10 Bose AM-6 Series III Sony STR-DG600 receiver JVC GR-HD1 HD camcorder Xbox 360 Pro / PS3 40 Gig HD DVD 0 / Blu Ray 15 Games 18 / Games 2 Gateway 901x HTPC (modified) Sling Box Pro w/HD Connect Cable Dish 211 receiver w/Absolute HD pack HP Pavilion dv-6000 laptop (HTPC2GO) Link-Theater Gallery - 100,000+ views Link-55 Restoration Updated 6/21/08

04-02-2008, 06:21 PM	#9
Emil High Definition is the definition of life. Join Date: Oct 2004 Location: Barrington, Il. Age: 57 Posts: 1,224	I'm resigning myself to the fact for the best quailty picture I'll need to go OTA (which I have as a backup) and BluRay. I just had a feeling that the quality of Comcast was going to slip and Directv is going to be better. I'll also be able to compare the two on Friday since I'll have both for a few days till I cancel Comcast. __________________ 60A2000 SXRD Klipsch PS3 DirecTV

04-02-2008, 03:20 PM	#6
BobY What's all this, then?... Join Date: Jan 2006 Posts: 6,197	Technically MPEG4 is heavier compression--but it is a more efficient codec so it can still look good.

04-02-2008, 04:59 PM	#7
Chris Gerhard High Definition is the definition of life. Join Date: Nov 2005 Posts: 8,206	I have both Comcast and DirecTV for the time being here in Little Rock and I would say Comcast picture quality for the few common HD channels is slightly better but the channel selection for DirecTV is far better. Both services compress too heavily and I hope DirecTV can improve. DirecTV has MGM HD and HDNet Movies and those two channels provide more of interest than all the Comcast offerings combined for me. Chris

04-03-2008, 02:53 PM	#10
mdustin How can anyone watch standard def? Join Date: Sep 2005 Location: sacramento, ca Posts: 17	Comcast tries to fit three HDTV into two I E-mailed the comcast Tech Support section with a specific question regarding your accusation. they could be lying, but immediately responded that they're not doing that. I'm in Sacramento....could it be our area is not affected? Last edited by mdustin; 04-03-2008 at 02:54 PM. Reason: typos

08-28-2009, 05:04 PM	#13
camper9 lurker Join Date: Aug 2008 Posts: 2	Has Comcast's HD quality improved since this thread was first started? Or is Comcast still sacrificing HD quality in order to have more "HD" channels?

08-30-2009, 05:37 PM	#14
firsTraveler High Definition is the definition of life. Join Date: Jan 2006 Posts: 429	Huh? Comcast has quality HD? Where? Quantity? Again where? Neither is here.

08-30-2009, 07:09 PM	#15
jstrazz I love my Samsung HD Join Date: Jun 2009 Posts: 33	Very happy with Dish Network and OTA.

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