[mythtv-users] Black blocks in video after CBS Buffalo (WIVB) adds first subchannel on new encoder

Jay Foster jayf0ster at roadrunner.com
Mon Oct 23 15:48:06 UTC 2017

On 10/22/2017 1:04 PM, Ian Evans wrote:
> Greetings MythTVizens, before I delve into the technical issue, if 
> you're in the Buffalo/Toronto area and record OTA you might be able to 
> duplicate this issue by recording Colbert or CBS This Morning.
> After adding their first subchannel (which was already on another 
> channel in the same city), I reached out to a WIVB station engineer to 
> confirm what was happening. He said there was a subchannel ballet 
> going on between the two stations, but yes, they had added the 
> subchannel after getting a new encoder last week. That's around the 
> same time I began noticing the problems. They are related to this 2016 
> thread: "Concert footage and video artifacts" 
> (http://lists.mythtv.org/pipermail/mythtv-users/2016-November/389597.html) 
> in which I described blocky video during fast transitions and got an 
> education in compression artifacts and bandwidth.
> That issue was mostly scene in fast music award transitions with 
> smashing cymbals and flashing stage lights, where the image would 
> suddenly look like an 8 bit game. But this issue is more subtle but 
> still annoying and noticeable and it's happening in moments it never 
> happened before. Again, if you're in the Buffalo/Toronto area try 
> watching the opening title sequence of Late Night with Stephen Colbert 
> or the "Morning Eye" opening segment of CBS This Morning. As the video 
> go from scene to scene, multiple black blocks appear in random part of 
> the image. I watch both shows regularly and this has just been 
> happening since the station switched to the new encoder.
> WIVB has only one subchannel and they're not trimming the bandwidth 
> too much as a 2 hr show has gone from about 14gigs to 12. Other 
> channels in the area have far more subchannels and I'm not seeing the 
> black blocks on their programming. The station engineer says he's not 
> seeing it with their off-the-air recordings but he'll keep looking. Is 
> there anything I can tweak on my end? Given that channels with more 
> subs don't have this issue could it be some setting/tweak on their new 
> encoder? I know this is hard to diagnose but I'd appreciate any tips.
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Over the years, I have seen anomalies and glitches on OTA broadcasts.  
What I found effective in getting them resolved is to make a short clip 
(a few seconds) of the problem and email it to the station engineer.  
When they can see what you are seeing, they are more likely able to 
resolve it.  Even some still frames showing the issue can help.

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