Comcast HD Quality Reduction: Details, Screenshots - Page 6  

Soon that isn't going to be an option. Cablecard sets are not going to work with the new cable technologies to do time slicing video over the cable system. I forget the exact name of the technology being tested, but it will render cablecard devices useless.

That problem even exists now where cablecard devices do not work with the advanced features of a cable system.

Keep in mind that the cablecard doesn't do any descrambling etc., that is actually done in the device, i.e., the TV. The cablecard is just the authorization portion of the whole setup.

Not necessarily true and yep. Take a look at all of the pizza-pan dishes at apartment complexes.

You ain't telling me somthing that I don't already know and have been trying to say for ages. As time goes on, many others will come to that conclusion as well.

Incorrect. 1080p is part of the original ATSC 18. The problem is that 1080p over ATSC using MPEG-2 isn't viable.

The tech you are speaking of is Switched Digital Video (SDV). It is true that current CableCard devices do not support 2-way operations, but tru2way (nee OCAP) devices are just around they corner and they will support all 2-way features of cable such as VOD, PPV, and SDV. Also, the CableCard is the part that does the descrambling; the host device is responsible for tuning and with tru2way it is also responsible for communication back to the cable provider. Further down the line, DCAS (Downloadable Conditional Access System) will replace the hardware CableCard with a bit of software that can be downloaded into compatible devices which will allow them to perform the decryption functions natively.

1080p24 and 1080p30 were part of the (never officially adopted) table of 18 ATSC resolutions, and they fit just fine in an ATSC payload. 1080p60 is not part of any broadcast standard and there is no foreseeable date when it will be added. 1080p60 will not fit with anything resembling watchable quality using MPEG2 in an ATSC payload.

The NBC HD feed is not low bitrate. The mux is doing about 52.99 Mbps. Not much is needed for the SD weather channel. I'm guessing about 22 Mbps for each HD, which is not at good as the ABC/CBS/CW HD feeds, but better than the 15 Mbps that many NBC stations are actually broadcasting, because of an SD stream.

ABC's current SD 8PSK mux is running 68 Mbps. The current HD mux is running 44.7 Mbps (one HD stream). When SD goes away and if they use the current SD transport for HD and they put two HD streams per mux, they'll drop their HD bitrate only a little bit from the current rate. But, it will drop none-the-less.

This is all conjecture, as I've not heard what ABC will do. Though it would seem logical to use their current 8PSK setup for doing HD.

thank god, i noticed this the other day and i was thinkin my tv was screwed up.

Ya, that's it.


Doesn't help the consumer that has current cablecard devices. Too bad that it isn't a module in the TV sets, etc., that can be swapped out.


Interesting, I was under the impression that the descrambling was done in the device and that the cablecard provided the keys when authorized by the cable company. Thinking about it, that would be a bonanza for hackers.


Sounds like a better solution.


Correct. I didn't say which of the 1080p rates I still have my Broadcasting & Cable's The Dawn of Digital Television 11/16/1998 supplement. Unfortunately I was lumping all of the 1080p together when I said it wasn't viable, forgetting what I originally read in the supplement only pertained to 1080/60p, which wasn't part of the ATSC 18 because it wasn't viable. Should have pulled out that guide first, before posting.

An interesting sentence in the supplement that no 1080i station is heeding, was as follows:

However, a football game broadcast live at 1080i/60 fields would take up nearly the full 19.4 Mbps and leave no room for multiplexing.

Try telling that to all the 1080i stations that have added sub channels. Management just doesn't care. This topic is complaining about Comcast, and potential other MSOs, but ATSC is heading for the same result because of multicasting.

To everyone who clicked on this thread and saw the initial screenshots from VRD take a look again the PQ is now much better and should look closer to what you see in your viewing set. Dscaler5 is used this time with MPC. Unfortunately . . . .



Comacast PQ (or most cable COs for that matter) compared to FIOS still sucks across the board

OMGTWFBBQ! That is one macroblocking mess on Comcast

22 is still well below the recommended 2:1 ratio to prevent concatenation errors between encode generations, even with multicasting stations. Bringing it back on topic, if these companies are actually doing a full decode/reencode rather than requantization, they are actually doing far worse damage than what happens with NBC's 22Mbit feed. At least NBC stations maintaining around 1.5:1, assuming 22->15, but on a channel like Discovery which originates at 13, recompressing that to 11 or 12 will add significant amounts of noise due to concatenation errors when the encoder has to try to replicate the already-present blocking and mosquito noise. At this point, if they insist on ruining the PQ, I would rather have them resize to 1440x1080i like E* and maintain something like a watchable picture rather than a sea of blocks swimming around my screen.

I have long thought that the 10+ year old ATSC should have been redone or scrapped in favor of a design that used compression. Back in the late 90's, mpeg2 was king, but now, H.264 has taken over and would prolly make 1080P broadcasts doable, and increase bitrates to bring quality up.... The only plus right now, is that current "crappy" looking HD, at least is a lot better then analog SD, but in some cases, not day and night better like people think.....

Yes it is, comparatively to CBS & ABC. I don't know where you got your info from, but it is wrong.

Is Comcast doing this 3-HD-per-mux in areas where switched digital video is fully deployed? I wonder if the current solution is just a stopgap measure. (wishful thinking)

I don't believe that Comcast has actually deployed SDV widely. The lack of SDV is probably why they are doing 3:1 to appear competitive to DirecTV. But once they get away with this 3:1 crap, then they will not likely revert to 2:1 after getting SDV.

'Tis true that it is below the 2:1 recommended ratio. When The WB was still around, their network feed was below 1:1 100% of the time (at least 17 Mbps for 1:1). So, what NBC is sending out is still better than what The WB did, but not as good as what ABC/CBS/CW does.

Even though Fox affiliates do not re-encode, the average bitrate that Fox is using sucks as well. If you look at the video fades, most of the time it is macroblock/artifact city.

What NBC is doing to their feed is a long way from the damage that Comcast is doing to the HD video.

But ATSC is using compression.


It was too late to think about scrapping, changing to H.264, since too many devices are out there for receiving MPEG-2 ATSC. If the government were to come along and say "Oops, we screwed up and now need to make all of the MPEG-2 ATSC tuners obsolete," the Boston Tea Party take 2 would probably happen.

That was a typo, I meant to say "better compression"

I know, the infrastructure is so big now, there will be no way to change for years, without consumer backlash...

Reference my response to coyoteaz.

My post had numbers, so the info was qualified. If the home viewer could get 22 Mbps, it would certainly be better than 15 Mbps that most NBC viewers are getting and much better than the 12 Mbps, and less, that Comcast is doing to their HD video.

So, should I have added, "in My Opinion..."? Probably.

Now, if NBC were to feed MPEG-4 to the affiliates, then the 22 Mbps, or thereabouts, should be good for converting to MPEG-2. I do not know what the recommended ratio is for going from MPEG-4 (H.264) to MPEG-2.

Are they going to get away with it? Consumer backlash and bad press about this horrible scheme is going to hopefully bite them in the ass.

I kinda figured that it what you meant to write.


So, so, true. For me, it would mean replacing two STBs. While the MyHD-130 card would still receive and capture ATSC, AFAIK, the current drivers wouldn't be able to display the MPEG-4. The captured stream would be viewable via other software. So, all would not be a total loss with the computer card.

But, it ain't gonna happen.

At three HD channels per mux MPEG-2 they would have better quality following the satellite guys lead and sending HD-lite, say maybe only 1440x1080i if they are not already doing so. Though I know that is not a popular idea here on AVS.

- Tom

Tom, DirecTV is not doing hdlite anymore, at least not on its mpeg4 channels, and I think not even on the old MPEG2 channels, now that they moved almost all HD channels to the new bird.

Please stop accusing them of doing HDlite unless you can provide some evidence they are still doing it.

I had this filed away, not sure where I got it from. It appears to be remote setups, but the post network operations center numbers look to be accurate.

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(1) FOX takes its 1.0Gbps (uncompressed) 720p truck feed, compresses it down to 73Mbps or less for their operations center, and then uplinks it to satellite at 14.6Mbps for distribution to local affiliates.

FOX affiliates pass this feed through without any extra processing or compression using specialized equipment provided by FOX.

(2) CBS takes a 1.5Gbps (uncompressed) 1080i truck feed, compresses it down to 45Mbps for their operations center, and then uplinks it to satellite at 45Mbps for distribution to affiliates.

CBS affiliates process and re-compress this 45Mbps feed to 19.4Mbps or less. Some CBS affiliates have newer/better encoders than others.

(3) ABC takes a 1Gbps (uncompressed) 720p feed at the truck, compresses it down to 45Mbps for their operations center, and then uplinks it to satellite at 40Mbps for distribution to affiliates.

ABC affiliates process and re-compress this 40Mbps feed to 19.4Mbps or less. Some ABC affiliates have newer/better encoders than others.

(4) NBC takes a 1.5Gbps (uncompressed) 1080i feed at the truck, compresses it down to ~38Mbps for their operations center, which then recompresses and uplinks it to satellite at 24Mbps for distribution to affiliates.

NBC affiliates process and re-compress this 24Mbps feed to 19.4Mbps or less. Some NBC affiliates have newer/better encoders than others, and since NBC was the first network to launch with high-def, a number of affiliates are still using [outdated] early generation encoders.

The higher the quality of the source, the better the result with compression. Because NBC distributes its feeds at lower bitrates, more bandwidth is needed to produce a comparable picture to say, CBS. Unfortunately, they rarely get it and quality suffers as a result.

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If I'm not mistaken, one of the reasons NBC uses a lower bitrate is because they use Ku band transmission whereas the others all go with C-band.

The old MPEG2 channels, like the original 8 DNS feeds(80-89) and channels like HDNet/HDNet Movies, UniversalHD, DiscHDT and HBO/SHO(70-79) are all still that funky HDLite 1280x1088 resolution. Basically the original channels that are/were in the old HD pack. There are new MPEG4 DNS channels in the 380 channel number range, but I'm not sure about HBO-W/SHO-W up in the 500 range.

We are in Central Illinois and were just switched over to Comcast from Insight, without of course any input from us. I will contact the Chief Engineer in our area and discuss the "compression" issue with him. I want to find out what, if anything, Comcast might be doing to affect the quality of our signal. Our signal appears to be different than it was with Insight Communications..........that is to say, not as crisp and sharp. Somehow.....call it a gut feeling I just don't trust Comcast! I will get back to you folks and fill you in with any new information I might glean!

What has C vs Ku have to do with it? All of the networks are using the full 40 MHz transponders (36 MHz modulated?). C is better for rain/snow fade. NBCs use of Ku has caused them trouble. NBC uplink even had a problem with a really strong rain storm. I thought my local affiliate was having reception trouble, but then it was reported on AVS that the uplink had trouble pushing through the rain Using 8PSK made that pushthru a little more troublesome.

NBC is even pushing through a higher payload than ABC/CBS/CW. Fox is pushing through the highest payload.

Unfortunately:

• Right now the GOALS database is over a year old
• The GOALS database does not show what is on what QAM - so you can't figure out how many HD channels per QAM.

Back to the diagnostic screens.

A&E HD on Cox is averaging between 6.5 and 8.5Mbit/s during The Matrix tonight. Anyone on Comcast able to take a look for comparison?

I have seen the future of cable HD and it looks like upconverted DVD.

someone should put this thread on Digg.