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Comcast HD Quality Reduction: Details, Screenshots - Page 2  

post #31 of 2079
Quote:
Originally Posted by sansri88 View Post

Also, instead of diagnostic screens, you can search up your system in the FCC COALS database.

Can you provide details on how to do this?
post #32 of 2079
Go here: https://fjallfoss.fcc.gov/csb/coals/index.html

Click on cable search in the left column. Type in your state, and then the type of filing is Annual Cable Operator Report. Look for the one that is your system name (mine is Comcast of New Jersey II). Within the report you can find detailed information on your system.
post #33 of 2079
Quote:
Originally Posted by sansri88 View Post

Go here: https://fjallfoss.fcc.gov/csb/coals/index.html

Click on cable search in the left column. Type in your state, and then the type of filing is Annual Cable Operator Report. Look for the one that is your system name (mine is Comcast of New Jersey II). Within the report you can find detailed information on your system.

Looks like some interesting info there, but with California systems it's rather useless since they all seem to be listed by number instead of anything to identify them by city/area.
post #34 of 2079
Cool. my system is 750 mhz
post #35 of 2079
Quote:
Originally Posted by keenan View Post

Looks like some interesting info there, but with California systems it's rather useless since they all seem to be listed by number instead of anything to identify them by city/area.

You can use your community identifier. It's on your bill. Mine is NJ329. If you search for that CUID, you can get your PSID (physical system ID). Do this to get the PSID:

1) Get the CUID off your bill
2) Input the CUID into the FCC Identifier.
3) For type of filing, look up the signal leakage report.

It will return results for your CUID. One of the columns on the search results will the the physical system ID. Copy it and go back to search. Then:

4) Input the PSID into the PSID box.
5) For type of filing look up the Annual Cable Operator Report.

That should get you the results you're looking for.
post #36 of 2079
Odd...when I do that, the result is not my system. It's nearby (in my state), but none of the Must Carry channels listed are on my [actual] system, and none of my [actual] Must Carry channels are listed anywhere for that PSID.
post #37 of 2079
Odd, but it works for me. I get Comcast of NJ II when I search for the PSID.
post #38 of 2079
I noticed the quality drop a few weeks ago. The only way to get ABC HD in Little Rock right now is through Comcast (the tower fell). So I record LOST on Thursday nights. The bit rate dropped from around 15mbps for the first episode to 9mbps for the second and subsequent episodes. In any motion there is some bad macroblocking. Better than SD but not the HD I've come to know and love
post #39 of 2079
Quote:
Originally Posted by sansri88 View Post

You can use your community identifier. It's on your bill. Mine is NJ329. If you search for that CUID, you can get your PSID (physical system ID). Do this to get the PSID:

1) Get the CUID off your bill
2) Input the CUID into the FCC Identifier.
3) For type of filing, look up the signal leakage report.

It will return results for your CUID. One of the columns on the search results will the the physical system ID. Copy it and go back to search. Then:

4) Input the PSID into the PSID box.
5) For type of filing look up the Annual Cable Operator Report.

That should get you the results you're looking for.

I finally found it, but it's inaccurate. It lumps my system in with surrounding communities that have more advanced systems so it doesn't reflect the true system status for Santa Rosa.
post #40 of 2079
Quote:
Originally Posted by bfdtv View Post

Last updated: March 16, 2008

Until recently, most Comcast systems passed all HD as is from the content provider, without any added compression or quality reduction. In response to competitive pressures from DirecTV and Verizon FiOS, Comcast recently decided to sacrifice some quality to improve quantity. By early April, most Comcast systems will recompress and degrade their HD, much like DirecTV and Dish Network do on their MPEG-2 channels. This creates room for new HD channels without the need to eliminate a significant number of analog channels.

Previously, Comcast allocated a maximum of two HD channels per 38.8Mbps QAM, so each channel had the full 19.4Mbps available if needed. Now, with the addition of new channels, Comcast is squeezing three HD channels into each 38.8Mbps QAM. Furthermore, some existing QAMs with two HD channels are being recompressed into ~25Mbps in preparation for new channel additions.

But what does that mean? How much difference is there, really?

To find out, I decided to compare the quality of the same programs on Comcast and Verizon FiOS. I recorded the same program from the same channel, at the same time, on both Comcast and Verizon FiOS in N. VA. I compared the size and bitrate of each MPEG-2 recording, as well as the subjective quality with video.

Note when I tested channels late last year, there were no differences between the two providers on HD. Any differences are new.


Bitrates

Average bitrates were obtained by comparing the size of each recording, in total bytes, and dividing by the total number of seconds reported by VideoRedo. Multiplied by 8 to convert MBps to Mbps.

Average Bitrates on FiOS v. Comcast
Code:
                            FiOS          Comcast           Difference

AETV HD                  18.66 Mbps      14.48 Mbps           -28.9%
Discovery HD             14.16 Mbps      10.43 Mbps           -35.8%
Discovery HD Theater     17.45 Mbps      12.60 Mbps           -38.5%
Food Network HD          14.32 Mbps      13.73 Mbps            -4.3%
National Geographic HD   11.39 Mbps      10.32 Mbps           -10.3%
Universal HD             12.72 Mbps      11.01 Mbps           -15.5%

Starz HD                 11.93 Mbps       9.76 Mbps           -22.2%
Comparisons for more channels will be added next week.

As of Tuesday, March 11, a few channels like ESPN-HD and Comcast Sportsnet HD still remain at full quality, identical on both Verizon FiOS and Comcast.




Comparison screenshots of more channels coming next week.


Initial Thoughts

It is obvious that the quality of the source signal plays a significant role in amount of degradation seen with Comcast's newly added compression. Sources like Discovery Channel (not Discovery Theater) and Universal HD are highly compressed to start with, and adding extra compression on top of that causes the picture to deteriorate rapidly with excess noise and detail loss. In contrast, higher-quality sources like Discovery Theater still look quite good, with the only obvious differences being added noise and loss of fine detail during motion.

Generally, 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 object transitions. 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 Discovery Theater images (above) are a good example of that. 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 excess motion blur seen with some video sequences on Comcast.




Sources

Round #1: Monday, March 9-11

A&ETV HD - The Sopranos: All Due Respect
Discovery HD - Mythbusters: James Bond Special
Discovery HD - The Human Body Pushing the Limits: Sensation
Discovery HD Theater - Fantastic Festivals of the World
Food Network HD - Challenge: Candy Castles
National Geographic HD - Naked Science: Birth of America
National Geographic HD - Naked Science: Glacier Meltdown
Universal HD - Action Sports
Starz HD - The Pursuit of Happiness


Round #2 coming next week...


STOP!



Do NOT use VRD to capture still images! It does not deinterlace properly resulting in less than accurate PQ still image. Not to mention it introduce artifacts like what you see in the picture.

Use MPC (Media Player Classic) with DScaler Mpeg2 Video Decoder instead. Check out my screenshot threads with Mpeg2 broadcast stills.


So no the PIX posted is not a true representation of the provider's PQ.
post #41 of 2079
Thread Starter 
Quote:
Originally Posted by Xylon View Post

Do NOT use VRD to capture still images! It does not deinterlace properly resulting in less than accurate PQ still image. Not to mention it introduce artifacts like what you see in the picture.

Use MPC (Media Player Classic) with DScaler Mpeg2 Video Decoder instead. Check out my screenshot threads with Mpeg2 broadcast stills.

I'm not sure why VideoRedo would introduce artifacts in the Comcast signal and not the FiOS signal?

I will redo the screenshots as you suggest tomorrow night. Thank you for the detailed instructions via pm.
post #42 of 2079
You got PM my friend.
post #43 of 2079
I have searched all over my Comcast bill and there is no CUID number listed.
post #44 of 2079
Quote:
Originally Posted by tcable View Post

Cool. my system is 750 mhz

Mine too. Thanks!
post #45 of 2079
Quote:
Originally Posted by ghudson666 View Post

I have searched all over my Comcast bill and there is no CUID number listed.

If your bill is anything like mine, it's at the very end. Mine is at the bottom of Page 2, in a section called "For Your Information". The CUID is on the right side, under "Franchise Authority Information" and is listed after the words "Your FCC Communitiy Unit is:".
post #46 of 2079
bfdtv,

great comparison photos...hopefully FiOS will be available in my area by the time I finish my HT build

I-Man
post #47 of 2079
Nice overall analysis from bfdtv. I could just barely notice differences between the inside-the-cave shots above--mostly differences in the rock surface textures. My Dell computer LCD is only set for 800X600. Downloaded the higher-rez file, but then erased it when installing new decoding software was required.

With all the computer tinkering going on, wonder what some spectrum analysis (SA) comparisons would reveal? SA plots frequencies/resolutions versus contrast, such as dr1394's plot of a 1920X1080 crowd scene (follow-on post). He used a free/low-cost software program (linked). Also wonder what plotting differences might appear (versus the shareware) using a high-end hardware analyzer, such as the HP model used by sspears to confirm fairly modest telecine resolutions from 1080/24p master tapes. -- John
post #48 of 2079
Quote:
Originally Posted by Xylon View Post

Do NOT use VRD to capture still images! It does not deinterlace properly resulting in less than accurate PQ still image. Not to mention it introduce artifacts like what you see in the picture.

I totally disagree. I get excellent image grabs.

You do NOT want to deinterlace 1080i. Deinterlacing can cause other problems. I can understand wanting to de-interlace when the source is video, since each field will be different and it is more evident with motion.

The images that I capture are from film sources or 23.976p video. For example:

http://vidiot.com/images/CBS-Sprite-080317-03.png
http://vidiot.com/OneTreeHill/images...ill-080226.png
http://vidiot.com/LifeIsWild/images/...ild-071202.png

With regard to the examples given, even if VRD's deinterlacing isn't as good, the point is that the images from the two source are obviously different. As with any experiment, you have to have a control. In this case, the control is the capture software. It is VRD, which will apply the exact same deinterlace function to both video sources. So, whatever it "adds" to the image will be the same for both.
post #49 of 2079
Quote:
Originally Posted by bfdtv View Post

I'm not sure why VideoRedo would introduce artifacts in the Comcast signal and not the FiOS signal?

It wouldn't. Whatever it does during the deinterlace function would be the same for both images.
post #50 of 2079
Quote:
Originally Posted by bfdtv View Post

See transponders 8, 16, 20, and 24 on AMC18.

Let's see, since I can't tune in DCII with my DVB-S2 card, I have to take an educated guess at the mux's parameters.

The mux is QPSK, so the most you can get out of it is about 45 Mbps. The CBS mux is 32762 SR, also at 3/4 FEC (IIRC). Since this mux is at 29270, I suspect the total payload is about 42 Mbps (I don't have the formula handy for figuring out the exact payload datarate).

Take away about 5 Mbps for overhead and audio, and you are left with about 37 Mbps for the three video streams, or about 12.3 Mbps. If VBR is used, then it can obviously divide out the bits where needed. But, if all three need bits and none of the streams has higher priority in the stat mux, then 12.3 Mbps is going to be the max.

12.3 Mbps is horrible. Even an OTA 1080i station with a single SD stream is going to allocate 15 Mbps to the HD video stream.

To provide the best quality to its customers, there should be no more than two HD streams on a QPSK mux. That will get it to the ATSC max bitrate that OTA has for a single video stream.

If they want to do three HD streams, then they should be doing 8PSK, where they could potentially double the bitrate payload. Going 8PSK at 70+ Mbps requires a very accruate TVRO system. Just ask Fox about their 8PSK problems.

Yep, looks like Comcast does not care about quality, only quantity.

I do not have cable or a pizza-pan system.
post #51 of 2079
Here is what it looks like in TSReader for the frequency that has Discovery HD, Sci Fi HD and USA HD.
LL
post #52 of 2079
Finally, apples to apples comparison! That's horrible, isn't it? A true testimate that Comcast's HDLite is inferior to DirecTV's HDLite. Quick question, bfdtv, the screen shot from Comcast, is that during a blocking event or are you seeing a different compression than I? I've never seen compression artifacts, my unwatchable Comcast moments are from excessive blocking. The reason I ask, it would be interesting to see if it is the Imagine Communications 3 into 1 squeeze that is causing the issue or Comcast's decision to begin bouncing molested channels off of satellites to our head-ends instead of letting them receive a clean signal and distributing it to us.

mrvideo, the 8PSK would probably not matter IF the degraded PQ is actually at CMC in Denver, where the 3-1 squeeze takes place. Our head-ends are receiving a feed off of AMC sats which is a pre-configured QAM channel per transponder. CMC sells these feeds as HITS Quantum and Quick Take. They are "in a box solutions" for smaller resell cable operators, MDU's, office buildings, etc. Comcast has decided to begin using CMC HITS to provide "national" channels to their head-ends as well. Using Imagine Communication's ICE Broadcast solution at CMC in Denver, three HD feeds (Sci-Fi, DiscoveryHD, and USAHD is the most scrutinized trio) are passed through Imagine's equipment to create one 38.8 Mbps constant bit-rate feed. While the feed itself is CBR, the "channels" inside of it are VBR (nulls fill it to a full 256QAM capable bit rate). In creating this feed, most of the FEC is stripped, MPEG2 compression is increased, and resolution may also be altered by Imagine's ICE "solution". This is then modulated and bounced off a satellite to be received by the head-end which re-modulates it into 256 QAM for our consumption. IF the problem is Imagine's solution, no change in modulation, bit-rate, or FEC from CMC's outbound satellite feed would matter, since it's the molestation of the data within that's the issue. If the problem is CMC's "packaging" of the Imagine Communications trio channels, then I could see where that would help. It's almost impossible to tell if the blocking and artifacts is being caused by Imagine's squeeze of 3 HD into 1 QAM or if it's CMC's packaging and poor delivery/reception from the SECOND sat bounce. Increasing the bit rate on CMC's outbound feed won't change the bit rate done by Imagine's ICE solution. NOW, to be fair, Imagine's products were designed to be installed in GROUND based head-ends and have their output STRAIGHT to fiber, not to satellite. Comcast decided to buy Imagine's ICE solution once, put it in Denver, then feed our headends through satellite rather than buying the equipment for each head-end.

If there was any hope of Imagine's triple-HD QAM solution of ever working, adding a satellite bounce after the squeeze pretty much killed it.
post #53 of 2079
Quote:
Originally Posted by Cyrl View Post

That is one you have to ask the FCC about, they(comcast) would really really love nothing more than to do that considering just how much bandwidth those channels suck down.

(bold by me to emphasize what i was answering)

Comcast has stated publicly that 20% of their "market" by end of year will loose analog Expanded Basic for it will become digital (roughly 40-45 QAMs freed on average). Comcast also publicly stated that 20% of "markets" by end of year will receive Docsis 3.0... they are probably the same "markets". The "lifeline" or "first 30" stations will remain analog transmission, just like Chicago, not to appease the FCC, but local franchise agreements who regulate these stations as a "utility" (where as non-must carries and PEG's are considered a luxuary; this is MUNICIPLE level stuff, so everyone is different here).

The "analog" is incorrect. The FCC clearly states that must-carry/PEG support for "analog TV" must continue, NOT analog transmission, and the cost of this support must be bourne by the operator. Read the Third Report and Order linked below, tons of information including Comcast complaints that do not sound like a company who wants to go to digital.

The 3:1 squeeze will more than likely never occur on local broadcast stations as the FCC mandates that no "material degredation" may occur during retransmission. This was strengthened within the Third Report and Order on DTV in December 2007. It's a good read on carriage, equipment, downconversion, etc.

http://hraunfoss.fcc.gov/edocs_publi...C-07-170A1.doc
post #54 of 2079
I've moved and no longer have Comcast. But, FWIW, my local Cox cable also sometimes has 3 HD channels in one physical RF channel. For instance I get FoxHD,PBSHD, and ABCHD, all as sub-channels of the same (+/- 38 mbps) sub-channel.

For anyone with a MyHD card there is an option to capture the entire stream instead on just one program, so you can actaually see the total bit rate or (usefull in some cases) record all 3 at once. Maybe someone on Comcast with a MyHD card could try this.

- Tom
post #55 of 2079
Quote:
Originally Posted by markofmayhem View Post

Finally, apples to apples comparison! That's horrible, isn't it? A true testimate that Comcast's HDLite is inferior to DirecTV's HDLite.

As far as I understood it, this was a comparison of video with additional compression by Comcast to untouched video from Verizon FIOS (which would be the same as OTA reception, but different than DirecTV.

Also, as far as I understand it, the person who did the comparison did not say anything about a reduction in resolution, only a reduction in the bit rate. Assuming that there is no reduction in resolution, this would not be "HDLite" as the generally accepted definition (reduced resolution, such as 1440x1080 or 1280x1080 versus proper 1920x1080) but just overly-compressed 1080i video.
post #56 of 2079
Yes, the Apples to Apples comparison was between Comcast and Fios. The horrible results show that Comcast's HDLite of Imagine's "bit rate shaping" is far inferior to DirecTV's HDLite of MPEG4, for MPEG4 is advanced enough to compress an HD video to sub-10 Mbps bitrates with very, VERY little loss to the end product. I personally have never seen an MPEG4 recompressed video look different than the MPEG2 provider's feed without REALLY inspecting it. Since most of us WATCH TV instead of inspecting it, it's a great solution to bit-rate reduction. Looks like FIOS is quickly becoming the last "True HD" supplier.

HDLite has many meanings to many individuals, at it's core, it is any molestation by the supplier. (increased compression, removal of FEC, reduction in resolution, interlacing, etc and is not limited to just resolution unless your a pro-cable poster trying to bash satellite)
post #57 of 2079
Quote:
Originally Posted by markofmayhem View Post

is not limited to just resolution unless your a pro-cable poster trying to bash satellite)

Actually, I'm a pro OTA-only poster... I understand that additional content is worth paying for, for some people. I do find it amusing and a bit satisfying I'll admit when I see the degraded product that people are willing to pay for.
post #58 of 2079
Quote:
Originally Posted by vj9999 View Post

Here is what it looks like in TSReader for the frequency that has Discovery HD, Sci Fi HD and USA HD.

You chopped off the bottom of the TSReader output that gives the total mux datarate.

But, it is interesting to note that my guess regarding the bitrates of the three video streams was higher than the actual bitrates.

Those bitrates are horrible for 1080i HD video.

Even if you reduced it to two streams, splitting one of the 10 Mbps streams, that would still only make the stream's bitrate in the 15-16 Mbps range. That still isn't good for 1080i HD video.

They need to get away from DCII and move to DVB-S2, which gives you 8PSK and about 63 Mbps mux total payload. If they went to an FEC of 7/8, that would get them near the 70+ Mbps total payload.

Thanks for the image, it added real data to my guess.
post #59 of 2079
Quote:
Originally Posted by markofmayhem View Post

the 8PSK would probably not matter IF the degraded PQ is actually at CMC in Denver, where the 3-1 squeeze takes place.

Because the bottom of the TSReader GUI was cut off, I do not know if it is reporting that the DCII stream is QAM or not. I'm going to take a stab and say that the actual satellite mux has zero QAM info in it. I'm guessing that the video and audio streams are taken from the sat receiver and fed directly into the headend QAM modulator.

Then you would be 100% correct, in that since the video has to fit within the 38.8 Mbps payload bitrate, no matter how good you can get it over the bird, the final product sucks.

My brain just wasn't thinking correctly about what I was reading.

It just annoys me how management just doesn't care about quality, only quantity. Funny how marketing will proudly say that "we have 150 HD channels" but fails to also say that these 150 channels are so full of macroblocks that they are hard to watch.

It isn't just Comcast that is doing this crap. In a discussion about the CBS comedy The Big Bang Theory, a member posted that the history visual that is at the start of the program is unwatchable on his CBS affiliate because that stupid station has THREE, count them, THREE SD subchannels along side the HD stream.

The almighty $$$ is killing digital quality.
post #60 of 2079
From what I've seen with Quantum HITS, the "receiving head-end" only has to modulate to 256QAM with no encoding/decoding needed, just modulation (from Q to 256). One transponder=one QAM which lowers the cost of equipment on the receiving end, but is this really ideal for sat comms? Is sat comm not subject to higher flunctuation and thus necessitates a higher quality feed (FEC and bitrate)? Imagine's solution was built directly for HFC. It's reduction in FEC, highly compressed video, and shaping of the full 256QAM pipe was never meant to be bounced off a bird. This combination that Comcast has created between less than ideal data over satellite and lower than acceptable bit rates is a real disaster thus far. USAHD and TNTHD had a showing of the "Bourne Identity" within a week of one another. The difference was night and day; not an issue on TNT while USA was actually unwatchable during the car chase scene. My promotional package price is up in June, I'm beginning to shop around now in preparation. It would still be interesting to know if it's the sat feed or the actual trio-QAM that's causing the issue. Cox and TWC have a few trio-QAM channels, are they seeing the same results?
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