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NBC distributes their feeds at over 20Mbps, so the network itself is not the problem (most of the time). Every broadcaster has 19.4Mbps to work with, but many affiliates divide that bandwidth between the HD feed and another SD feed for weather or traffic.

About 16Mbps (and 17+Mbps is preferable) is required to produce a MPEG-2 picture with consistent quality on live video broadcasts like sports. If your broadcaster or cable company is supplying significantly less than 16Mbps, then quality will suffer on football. You -- and your broadcaster or cable company -- may not have noticed the problem before because film-sourced material like movies and series programming requires less bandwidth.

Some cable providers re-compress the local network feed while others do not. If your local NBC affiliate is taking that >20Mbps NBC feed and compressing it down to 12Mbps -- which is completely inadequate for sports -- then they are to blame for the poor quality. On the other hand, if your local NBC affiliate is sending that feed at 16Mbps or 17Mbps, and your cable provider is re-compressing that down to 12-13Mbps, then they (the cable provider) is to blame.

How do you find out who is responsible for the poor quality so you know where to direct your complaint? Simple, you record the same program from cable and off-air (antenna) and compare the file sizes by hitting Info. Higher quality recordings consume more space.

bfdtv said:
The Tivo makes it easy to compare the bitrate (i.e. quality) of your OTA locals and cable locals. How do you do it?

  1. Create a recording for the same program (at the same time) on both the OTA channel and cable channel.
  2. Once the recordings are complete, you can see the file sizes for each recording by clicking on the recording and then hitting Info. You may need to page down.
  3. Bitrate = Recording Size on TiVo INFO Screen * 8000 / (minutes * 60)
By comparing the file sizes of the same program recorded from cable and off-air (antenna), you can determine who is to blame for the poor quality.

If the recording sizes are the same, then the local NBC affiliate is to blame, and you should call and complain to their engineering department (usually linked on their web site) -- tell them their feed looks ok for series, but is unwatchable with pixelization and macroblocking during sports. If their engineering department does nothing, then you send the same complaint to the station manager. If the station manager does nothing, you send the message to their boss -- the parent company who owns the station, usually listed at the bottom of their web page.

If the recording from the cable company is smaller in size, then that means they are degrading the quality of the feed. They may not be entirely responsible for the poor quality (depending on the off-air bitrate), but they are contributing to it.
 

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MickeS said:
bkdtv, thanks for your input.

I just checked 4 OTA recordings of "The Tonight Show" from the NBC affiliate in Tucson, AZ. They range in size from 7.90 to 7.94 GB. That would give a bitrate of roughly 17.44 Mbps (they are 62 minutes long).

I will record "The Tonight Show" tonight off of TWC here in San Antonio. Even though they are from different broadcast markets, I assume that the OTA/cable comparison should still be valid?
NFL football on NBC should do pretty well in 17.4Mbps ABR.

The bitrate varies on Jay Leno from one night to the next, depending on the content complexity of each show. However, in my experience, the spread from one night to the next is pretty small -- typically less than 0.3 Mbps ABR.

Many 750MHz Time Warner systems use statistical multiplexing to squeeze three HD channels in every 38.8Mbps QAM slot. Bandwidth is allocated as it is required; if only one channel requires 17+Mbps, and the other two need just 10Mbps to produce a quality picture, then PQ remains good. However, if all three channels require 16+Mbps at the same time, then each is bit-starved with less than 13Mbps and a softer picture with macroblocking is the result.

For that reason, recording Jay Leno -- a late night program -- from TWC may not be the best way to show you what is happening during primetime hours, because if that is the only channel on that QAM slot running high-def video, it will have more bits available. A better test would compare recordings made during primetime, when more high-definition programming is shown across different channels.

There was a TWC system in NY that stuck one of the HD RSNs on the same QAM slot with two local networks. The PQ on the local networks would look fine most of the time, but it would degrade badly -- especially on live video broadcasts like sports -- whenever there was an actual high-definition game shown on the RSN.
 

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MickeS said:
I recorded The Tonight Show off of TWC cable in San Antonio, and the size was 5.89GB. So the bitrate on cable here is 12.97 Mbps, compared to the 17.44 Mbps I had OTA in Tucson.
It's unfortunate the TWC in your area degrades their picture to such a large degree. Although cable typically offers a better HD picture than DirecTV, I think in your case, your picture would likely be better with DirecTV.

I don't suppose Verizon FiOS is available in your area? They don't touch the OTA signal (i.e. identical to off-air bitrate).

I think it's pretty safe to say that my cable company is compressing the signal too much and that it is what is causing this lousy PQ (probably in combination with other factors when it came to the NFL game). I can't imagine that 12.97 Mbps will be enough to even show artifact-free regular programming in 1920*1080?
That ~13 Mbps can be sufficient to produce a good picture on episodic series and movies, but it is completely inadequate for live high-definition 1080i video.

Does anyone think that it's worth trying to talk to anyone at TWC regarding this? I mean, obviously they know what they are doing, I guess they just figure most people don't have less compressed OTA to compare to, and will accept this crap.
I would complain. That bitrate is just not acceptable for a 1080i channel.

If you are able to receive channels OTA, I would set your season passes to use those channels instead.
 

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MickeS said:
I keep bringing this up... :)

I recorded 1 NFL game on Fox today, 1 on NBC, and the PGA tournament on NBC.

Bitrate at NBC was just under 13 Mbps for both broadcasts, and on Fox it was just over 13 Mbps.

The NBC broadcasts both looked pretty crappy. LOTS of artifacts again, and generally unpleasant to look at as soon as there was motion.
Any 1080i feed broadcast at less than 16Mbps isn't going to produce a consistently good picture on high-definition video with motion, like football. Hopefully, TWC is the problem in your area so you can eliminate it with that antenna.

MickeS said:
The NFL game on Fox looked very good - few if any motion artifacts of the kind I saw on NBCs broadcasts. They broadcast in 720p. Does the fact that they broadcast in 720p vs 1080i on NBC create less artifacts at around the same bitrate? I'm starting to doubt that the lower bitrate is the only thing that's wrong with the NBC broadcasts...
NBC distributes a 20+ Mbps feed and the affiliates compress it as they see fit. Some affiliates deliver that feed at 19.4Mbps, but 16-17Mbps is probably average.

FOX is unique in how it distributes its HDTV feed. That network distributes their feed at 14.6 Mbps peak, with an average bitrate 10-14Mbps depending on the content. However, unlike ABC, CBS, and NBC, the affiliates do not re-compress these feeds. FOX supplied affiliates with the equipment to pass this signal through without any extra processing or compression. As a result, the quality on FOX's high-definition programming tends to look just as good on every affiliate.
 

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mike_camden said:
Regardless, the PQ on the Fox and the CBS games were head and shoulders above that of NBC, and bit rate doesn't have anything to do with it (as the bit rates for all three were similar).
If the bit rate was similar on FOX and NBC, then that would be the reason quality was so bad.

High-definition 1080i video broadcasts require significantly more bandwidth to maintain a quality picture. A 720p60 football game will look great in 13-14Mbps from FOX, but will look horrific with less than 16Mbps from NBC.

I have seen the NBC source feed and it looks excellent. It is absolutely not a case of crap in, crap out.

Summary of Video Distribution at the Big Four
  1. FOX takes a 1Gbps (uncompressed) 720p feed at the truck, compresses it down to 73Mbps for the FOX operations center, which then compresses it down to a max of 14.6Mbps with industrial grade ($$$$) encoders. This signal is uplinked to satellite for affiliates.

    FOX affiliates pass this feed through without any extra processing or compression using specialized equipment provided by FOX corporate.
  2. CBS takes a 1.5Gbps (uncompressed) 1080i feed at the truck, compresses it down to 45Mbps for the CBS operations center, which 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. With CBS, a bitrate of ~12Mbps is typically required to produce a good 1080i picture on film-sourced series content, while a bitrate of >16Mbps is required to produce a good picture on high-definition 1080i video with movement, like football.
  3. ABC takes a 1Gbps (uncompressed) 720p feed at the truck, compresses it down to 45Mbps for the ABC operations center, which then uplinks it to satellite at 45Mbps(?) for distribution to affiliates.

    ABC affiliates process and re-compress this 45Mbps feed to 19.4Mbps or less. Some ABC affiliates have newer/better encoders than others. With ABC, a bitrate of 9-10Mbps is typically required to produce a good 720p picture on film-sourced series content, while a bitrate of 13-14Mbps is required to produce a good picture on high-definition 720p video with movement, like football.
  4. NBC takes a 1.5Gbps (uncompressed) 1080i feed at the truck, compresses it down to ~38Mbps for the NBC 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 Harris MPEG-2 encoders.

    With NBC, a bitrate of ~13-14Mbps is typically required to produce a good picture on film-sourced series content, while a bitrate of 16-18Mbps is required to produce a good picture on high-definition video with movement, like football.
As a result, the NBC feed will never look as good as the other feeds with an equivalent level of compression. More bandwidth is required for NBC to produce a comparable picture to CBS.

If you've ever done any video or image compression, you know that you get better results when you start with a higher quality, less compressed source. The fewer the compression steps, the better the result. For example, you get a far better picture when compressing a 500Kb PNG to 50Kb JPEG than you get when compressing a 50Kb JPEG of the same image down to 30Kb. The same principle applies applies with high-definition signal distribution.
 

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I was corresponding with the local NBC affiliate, and asked about this. Here's the reply:

12 MBps seems really low for OTA, even if they do have one subchannel in use. I can't argue with him yet though, as I haven't seen the OTA broadcast here...
Would TWC be doing something else with the signal that could cause the problems? Maybe something like constant bitrate versus variable bit rate (not sure if that is relevant here)?
He told you that their station encoder is set to 12Mbps. That is barely adequate for series programming, and completely inadequate for 1080i video like sports.

As I noted in my previous post, the NBC network feed sent to every affiliate is about 24Mbps. At least 16Mbps is needed to produce an acceptable picture on most NBC sports broadcasts, and 17+Mbps is preferred. At 12Mbps, 1080i sports will look like garbage.
 

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Thanks for that information.

I guess I will respond and ask why they have the encoder set to such a low bitrate (although I can guess the answer). I wonder if the guy is not watching at the right distance. I view at just over the SMPTE recommended distance for HD (about 6 feet for my 42" screen) to take advantage of the full resolution, which is closer than most people.
Unfortunately, most broadcast stations still use small screens (typically under 20") to monitor their signals.

If you are able to talk to the engineer on the phone, you might invite him (and the station manager) to visit your house to see the quality of their high-definition sports broadcast on a larger screen.
 

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What is the problem with HBO HD? Movies look like crap -- artifacts, blurred motion, pixelization. I was so pysched to get a larger hard drive and start recording movies, but they look awful. Much worse that standard DVD.
Who is your provider? Sounds like they are degrading the quality of that channel.
 

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I hate to say this, but I've noticed the same thing since getting my S3.

I was using an SA 8300HD prior to the S3. While I hated the SA box's interface, my recollection is that the picture quality is somewhat better with HD programming, ESPECIALLY at times of rapid motion.
Picture quality is as good as my Motorola DVR in fixed mode, and better in native mode.

Fixed 720p mode will degrade resolution on 1080i channels (effectively downconverting them to 540p), while fixed 1080i mode will degrade motion on 720p60 channels.

Some providers recently increased their compression levels to make room for new HD channels.
 

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Cablevision. The other HD signals are great. Just HBO is awful.
They may have squeezed HBO in with some other channels.

Cable providers like Cablevision have 38.8Mbps available per QAM slot. As distributed by satellite, HBO, Showtime, and Starz all require 10-11Mbps average and about 14.5Mbps peak (i.e. during action).

The bean counters at cable companies think it is wasteful to stick HBO and SHO on one 38.8Mbps QAM channel, because that only uses 20-22Mbps average and 29Mbps worse-case. The remainder of the 38.8Mbps is unused.

A number of cable providers, including Cablevision, Cox, and Time Warner have installed rate shaping equipment to squeeze a third channel -- say, HBO, SHO, and Starz -- into the same 38.8Mbps QAM slot. When one of those channels need more bits -- such as during action or movement -- pixelization and blocking results because the needed bandwidth isn't available. In this case, the provider has prioritized quantity over quality.

I suspect Cablevision added new HD channels at around the same time this problem began.
 
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