Channel issue - Bubbster

Reception, channel detection, network issues, CableCARD setup, etc.
Bubbster
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Joined: Mon Nov 08, 2010 9:34 am

Channel issue - Bubbster

Postby Bubbster » Sun Sep 02, 2018 9:18 am

I have a very similar situation here. The NBC affiliate plays perfect on TV, on Win7 MC it plays ok until there is fast motion like sports, then it pixelates occasionally.

I was beginning to wonder if they use a different hardware setup at that station that causes my media center to not be able to keep up. I then noticed it on the HDHR software on another PC on the same lan. To me, that narrows it down to the HDHR having an issue with this one station, WDTN-DT if it matters.

Any help please? This will drive me crazy when Sunday night Football starts!

Bubbster
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Re: Antenna to TV IS OK Antenna to HR not OK for 1 channel

Postby Bubbster » Sun Sep 02, 2018 2:04 pm

I was thinking the local NBC affiliates might be updating their hardware and using newer codecs to compress, requiring more cpu power. Whatever it is I'm not happy about it. Channel 2.1 used to be the best looking and performing station in the market.

Im getting a good signal too, using hdhomerun_config_gui.exe to measure. Just can't handle the faster motion, and my Sammy TV can. Same antenna.

jasonl
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Re: Channel issue - Bubbster

Postby jasonl » Tue Sep 04, 2018 3:20 pm

Please enable the sending of diagnostic data and run a channel scan (see viewtopic.php?f=15&t=69066) then watch live TV on the problem channel for 10 minutes. Reply back with the device ID for your HDHomeRun and we will check the logs.

TBlankenheim
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Re: Channel issue - Bubbster

Postby TBlankenheim » Tue Sep 04, 2018 9:01 pm

It is possible I have a similar problem with the NBC affiliate in the Madison WI market.

I notice pixelation usually in fast scene swipes. I have observed this on the OTA channel using my old HDHR3-US (15.1) and over the cable channel from my HDHR3-CC (615). I have observed these artifacts on Live TV or in recordings.

But here is the kicker, I am suspicious of some strange issue with the NVIDIA MPEG-2 decoder. I have this problem if I watch Live TV or DVR recordings on Windows 10 clients using GTX 1050 and GTX 1070 video cards. I have also observed this problem on my NVIDIA Shield TV. If I watch using my laptop which uses NVIDIA GeForce 9650M GT graphics, I DO NOT have the problem.

Also, VLC exhibits the same problem on the Windows 10 clients using the GTX 1050 or 1070.

If I watch this channel via DLNA to my Smart TVs, there is also NO PROBLEM.

Another bizarre twist, if I transcode the DVR recordings to H.264, the problem goes away. So I'm at a bit of a loss the best way to proceed.

I do have a 45 second MPEG-2 clip that exhibits the problem. I also have the same clip transcoded to H.264 for comparison. Please let me know the best way to make this clips available.

Tom

gtb
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Re: Channel issue - Bubbster

Postby gtb » Tue Sep 04, 2018 9:34 pm

But here is the kicker, I am suspicious of some strange issue with the NVIDIA MPEG-2 decoder.
Every generation of nVidia (all manufacturers, actually) VPUs(*), reportedly (by those with much much better lab equipment than I do) implement the codecs slightly differently (we will ignore the cases where the VPU is too slow to actually decode and post process high resolution high bitrate content). And some of the cards offload different parts of the VPU decode and/or post-processing to various parts of the entire system (sometimes the CPU does some of the decode/post-processing, and sometimes the GPU does some of the decode/post-processing). So, you could be correct.

However, the other possibility is that the station itself is encoding it poorly (i.e. out of technical specs). The encoders most broadcasters use has hundreds of logical knobs to fine tune the encoding. While the defaults may work for some, some TV broadcast engineers will twiddle and adjust and find tune for months, which can result in a stream that has something slightly wrong with it which no two solutions will handle the same (so your transcoding solution my do things better for this case). And, sometimes, it is the hardware encoders firmware that is doing it wrong (so the station itself is a victim).

If you have a sample which reliably shows the artifacts, you should provide it to nVidia (I think you have to signup for their developer forums) for their information and evaluation. In some cases they may be able to fix the decode, and in others it may require a new generation of device (try a RTX 2080 and let us know?), and sometimes they may be able to tell you what to go suggest to the stations engineer to change.

(*) VPU is the (dedicated) Video Processing Unit.

TBlankenheim
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Re: Channel issue - Bubbster

Postby TBlankenheim » Wed Sep 05, 2018 10:26 am

If you have a sample which reliably shows the artifacts, you should provide it to nVidia (I think you have to signup for their developer forums) for their information and evaluation.
I can certainly pursue taking this route, but being just a lowly end user, I am not holding my breath. Before I go down that road, it would be nice to gather additional data regarding hardware that exhibits the problem vs hardware that does not. If anyone cares to give it a try, I have posted the video clip up on Google Drive. It is about 55 MB in size.

https://drive.google.com/open?id=1Iy1gS ... Am-Ws0KNjk

Thanks!

gtb
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Re: Channel issue - Bubbster

Postby gtb » Wed Sep 05, 2018 12:01 pm

I can certainly pursue taking this route, but being just a lowly end user, I am not holding my breath.
nvidia accepts samples from almost anyone, but as you say, you may not get a directed personal response (just some future improvements, if possible), and it may (will) take some time for them to even get to analyzing the sample. But without the samples, nvidia has no way to know there are issues to look at, so always send the samples.

A possibly interesting issue (to me) is that there seems to be a few stations around the country reporting these artifacts with nvidia cards, which suggests that this may be related to a specific encoder issue (there are only a few manufacturers that broadcast engineers trust/use, and it is possible that all the reports are using the same model encoder, or with the same settings, or ???).

One of the reports I recalled was also from a NBC station that recently changed to be an O&O station (which likely got a large influx of money to upgrade their infrastructure and possibly encoders, so it is all different now).

jasonl
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Re: Channel issue - Bubbster

Postby jasonl » Wed Sep 05, 2018 4:42 pm

We did confirm an issue with WFAA in Dallas is something on the NVIDIA side and have sent a sample to NVIDIA to investigate.

One thing you can check on the NVIDIA systems is to disable DXVA decoding in VLC. If it is indeed an NVIDIA decoder issue, then VLC doing software decode should not exhibit the problem. Removing the MPEG2 decoder pack on the Win10 PC should do the same thing when using the HDHomeRun app.

Bubbster
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Re: Channel issue - Bubbster

Postby Bubbster » Wed Sep 05, 2018 5:42 pm

Please enable the sending of diagnostic data and run a channel scan (see viewtopic.php?f=15&t=69066) then watch live TV on the problem channel for 10 minutes. Reply back with the device ID for your HDHomeRun and we will check the logs.
I'll get to this over the weekend, then I'll try to understand the Nvidia issues chat also added to this thread. TIA!

TBlankenheim
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Re: Channel issue - Bubbster

Postby TBlankenheim » Wed Sep 05, 2018 7:32 pm

One thing you can check on the NVIDIA systems is to disable DXVA decoding in VLC. If it is indeed an NVIDIA decoder issue, then VLC doing software decode should not exhibit the problem. Removing the MPEG2 decoder pack on the Win10 PC should do the same thing when using the HDHomeRun app.
Disabling DXVA in VLC and removing the MPEG-2 decoder pack solved the problem. Is there an easy way to do this on a Shield TV?

I'm not terribly fond of this solution just for a single channel. Hopefully NVIDIA acknowledges this and provides a solution. Especially for the Shield TV box. I would like to use the Shield TV to replace the cable company STBs.

Bubbster
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Re: Channel issue - Bubbster

Postby Bubbster » Thu Sep 06, 2018 3:59 am

Another thought before I tinker this weekend... I guess I should remove a codec pack I have installed? The cleanest one I've found for the last 10 years is Shark's codec pack, standard, only really have it installed to play mkv's on Win7 Media Center.

It doesn't touch the Win7 MCE codecs, where my issue is with the NBC station*. I'll remove it first and test before I do the diag send to SD.


*Also get this same pixelation over my gigabit lan to my personal box where I only use the HDHR viewer or occasionally VLC.

gtb
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Re: Channel issue - Bubbster

Postby gtb » Thu Sep 06, 2018 10:03 am

Hopefully NVIDIA acknowledges this and provides a solution.
Are you stating that you have done the frame by frame evaluation and been able to show that it is not an encoder issue (and nvidia is just the victim)? I have not tried to do so, but it would be valuable if you can show via your analysis that a 100% valid (under the detailed specs) stream is not being properly decoded. Otherwise, asking nvidia to support invalid streams is the wrong fix, and you need to ask (say) harmonic to issue a fix.

TBlankenheim
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Re: Channel issue - Bubbster

Postby TBlankenheim » Thu Sep 06, 2018 11:17 am

Are you stating that you have done the frame by frame evaluation and been able to show that it is not an encoder issue (and nvidia is just the victim)?
I wish I had that technical ability! I was basing my remark on jasonl's reply a few posts back.
We did confirm an issue with WFAA in Dallas is something on the NVIDIA side and have sent a sample to NVIDIA to investigate.

Bubbster
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Re: Channel issue - Bubbster

Postby Bubbster » Thu Sep 06, 2018 3:42 pm

In my situation, Win7 Media Center, how could it be an nvidia issue when it records the pixelation?

gtb
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Re: Channel issue - Bubbster

Postby gtb » Thu Sep 06, 2018 7:25 pm

Are you stating that you have done the frame by frame evaluation and been able to show that it is not an encoder issue (and nvidia is just the victim)?
I wish I had that technical ability! I was basing my remark on jasonl's reply a few posts back.
We did confirm an issue with WFAA in Dallas is something on the NVIDIA side and have sent a sample to NVIDIA to investigate.
The way I read it, he simply confirmed they observed the issue, and made a report, not the cause. In which case we are back to limited knowledge.


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