HDHR3 Prime. How do I troubleshoot pixelation on DRM channel with dark background?

Reception, channel detection, network issues, CableCARD setup, etc.
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ian
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Joined: Thu Jul 19, 2012 12:45 pm

HDHR3 Prime. How do I troubleshoot pixelation on DRM channel with dark background?

Post by ian »

I have a long term issue with pixelation on certain DRM channels, particularly HBO, Showtime etc. I do not believe this is necessarily an HDHomeRun problem, but I need help figuring out how to troubleshoot it.

My setup.
HDHR3 Prime. I use a Windows 7 PC and Windows Media Center. However I have seen the same issue by going to the Tuner directly using the Windows 10 HDHomeRun app and viewing the channels live on a different PC. For this reason I am inclined to believe this is not a Windows Media, or even PC specific issue. All the PCs and the tuner are connected with wired gigabit ethernet.

I only see the issue on DRM channels, but it does not occur on all DRM channels. I mainly watch pre-recorded content. I see it most often when watching the end credits of a movie, with light coloured text on a black background, though I also see it during dark scenes of a movie. As the credits proceed they will glitch with pixelation as the words freeze and smear for a few seconds. Usually after a few seconds (next I-frame?) the picture resolves and continues as normal. I have changed video card twice in my HTPC, but the problem persists, though manifests a little differently with each card. The Nvidia GTX1050ti was much worse than the current AMD Radeon RX460.

The glitch is encoded in the recording, as I can watch the same video several times, and the glitches will manifest in a similar way in the same place.

I have the same issue on a different Windows 10 PC, when using the HDHomeRun app on my laptop going direct to the tuner. The glitching is much the same on the same channels.

I would like to figure out the source of the problem. I have experienced it for several years. I think I have changed the cable card within that period. I have talked to my cable operator, RCN, but I have made no headway, as I do not know how to describe the issue in an actionable way.

My thoughts are that it is either a cable issue, a cablecard issue, or an issue with the HDHomerun Prime3. But I am stuck at this point, trying to figure out how to troubleshoot it from here.

I'd appreciate any ideas on how to proceed with troubleshooting.

Thanks,
Ian


Ian

jasonl
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Re: HDHR3 Prime. How do I troubleshoot pixelation on DRM channel with dark background?

Post by jasonl »

If it's happening across multiple devices and multiple GPUs, I'd be inclined to blame the cable provider's encoder. Encoders rely on technology called statistical multiplexing to dynamically allocate bits between different services that are carried on the same channel. They monitor the content of all of the video streams and dynamically adjust how the bits are allocated to try to maximize the quality on all of the channels. Besides motion, dark vs. light also plays a part, since the human eye has a harder time making out detail in dark areas, so the encoder can give less bits to dark scenes and more to bright. If the encoders aren't configured with a reasonable minimum data rate, then super dark/low motion scenes (such as the credits) may get almost nothing allocated, and as a result it looks like something you found on Kazaa circa 2001.

ian
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Re: HDHR3 Prime. How do I troubleshoot pixelation on DRM channel with dark background?

Post by ian »

Thanks Jason,
My takeaway is that there may be nothing I can do about this, it is just 'baked in' to my cable service. Unfortunately, as I have no cable box, I have no way of confirming this is a cable plant fault. My assumption is that if I were to connect a cable box I would expect to see the same issue with the cable box. Is this correct?

I'd also like to confirm that actual glitching is expected from statistical multiplexing. It is not just smearing of the image, there is actual picture breakup and stalling which usually recovers, though on some occasions the stream seems to be so badly corrupted that you have to jump or skip over the broken section to continue.

Is there any way you, or anyone else, could think of that would allow me to prove this. I have found in the past that RCN are responsive to my issues, but I'd like to give them some sort of proof.

Thanks

Karter
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Re: HDHR3 Prime. How do I troubleshoot pixelation on DRM channel with dark background?

Post by Karter »

copied this from the forum guide
viewtopic.php?f=116&t=12216

might just be a weak signal


Weak Signal From Cable Company

I was getting a consistant weak signal from Time Warner Cable. My signals were in the 70% range, the highest in the low 80%'s. I was getting the "Weak Signal" (among other errors) in MC so I ended up purchasing an 8-port Channel Master in-line amplifier. This pushed all my signals to really good levels. My weakest station (frequency) is now in the low 90%'s with most channels pegged at 100%. I still get pop-ups of course, but not nearly as many and at acceptable levels.

Vendors for amplifiers include:

https://www.channelmaster.com/Amplifiers_s/23.htm
http://www.pacificcable.com/More_Pages/ ... ifier.html

NOTE:
Your signal quality reading in the HDHomeRun menus should be at 100% (or close to it). If it is not, the amplifier will just amplify a bad signal. If this is the case, a call to your cable company, or you yourself looking into cable run troubles, etc is in order. Amplifiers are great for those getting weak but good/great quality signals.

nickk
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Re: HDHR3 Prime. How do I troubleshoot pixelation on DRM channel with dark background?

Post by nickk »

Are the pixelation blocks also a darkish color?

It sounds like the encoder is overcompressing the dark areas of the video.

About all you can do is turn the brightness down so it isn't as visible or complain to your cable provider.

Nick

jasonl
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Re: HDHR3 Prime. How do I troubleshoot pixelation on DRM channel with dark background?

Post by jasonl »

Assuming it's an encode problem, you should see similar issues on a cable box, though not necessarily identical since the MPEG2 spec allows different decoders to produce different outputs given the same input, and once that output is obtained, it gets fed into other things that might do postprocessing to try to clean up some of the noise, and also at some point there's a deinterlacer involved to convert 1080i to 1080p for your display.

For what it's worth, years ago when I had Fios some of their premium channels had the same issue, and I'm pretty sure it also affected both non-DRM channels like Showtime and DRM channels like HBO. I never really bothered to do anything about it because it was only the credits and I dropped those channels after the free trial was over anyway.

ian
Posts: 12
Joined: Thu Jul 19, 2012 12:45 pm

Re: HDHR3 Prime. How do I troubleshoot pixelation on DRM channel with dark background?

Post by ian »

Thanks for the responses.

Nickk:
The pixelation blocks vary depending on the GPU. With the Radeon, they are mostly black. Using the Nvidia they were often a very bright green!

Karter:
The main menu status is
Status
Card Authentication success
Card OOB Lock weak
Card Validation success

I am now wondering about a weak signal. Is 65% not enough?

Looking at the CableCard Menu I get these results.
CableCARD Status
Card Manufacturer Arris/Motorola
Card Authentication success
Card Validation success
3DES encryption supported
OOB Frequency 75.250 MHz
OOB Lock 2.048 Mbps
Signal Strength 65% (-21.3 dBmV)
Signal Quality 98% (30.3 dB)
Channel List cablecard-oob

I actually previously (for most of the time period I have had this issue) had a coax amplifier connected but disconnected it as I thought that could be the problem.
It is this one, though it is currently disconnected and bypassed.
https://www.pctinternational.com/product/pct-ma2-m/
I could reconnect it but it does not solve the problem.

If I tune to a problem channel it seems to be 100% signal? Most of the other DRM channels are 100% Signal Quality, though a couple are at 98% or even as low as 96%. But the main problem channel is 100% Signal Quality.

Virtual Channel 700 HBO HD
Frequency 459.000 MHz
Program Number 2
Authorization subscribed
CCI Protection protected-copyonce
Modulation Lock qam256
PCR Lock locked
Signal Strength 100% (0.5 dBmV)
Signal Quality 100% (36.6 dB)
Symbol Quality 100%
Streaming Rate 6.927 Mbps
Resource Lock 192.168.1.117

Thanks

jasonl
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Re: HDHR3 Prime. How do I troubleshoot pixelation on DRM channel with dark background?

Post by jasonl »

The OOB signal strength doesn't really matter for several reasons:
  • The data it carries is background information like authorizations for the CableCARD and the channel lineup, not anything that would directly impact live viewing except when you're on the phone with the cable provider and they're making changes
  • The modulation scheme it uses is much more tolerant of poor signal than a real cable channel. It can work with the signal strength down in the 30s.
  • The signal strength measurement on the OOB channel is not reliable in all circumstances. The out of band signal is shoehorned into a gap between channels 4 and 5. If your cable provider leaves one or both of those channels empty (as many do), then the tuner can underreport the strength due to limitations in how it measures strength. The quality is still high which is what matters.
The numbers that really matter are on the actual channel, and yours are perfect. You should check that page at various points of watching a movie live and see how much the streaming rate varies. 6.9 is already low for an HD channel, but I bet it goes much lower during the credits.

ian
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Joined: Thu Jul 19, 2012 12:45 pm

Re: HDHR3 Prime. How do I troubleshoot pixelation on DRM channel with dark background?

Post by ian »

You are all correct, after watching the tuner status screen during the dark parts of the credits, the bit rates drop really low, to around 1.2, and things smear. It is nice to know the cause, even though I can do nothing about it.

Thanks for the help,
Ian

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