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

Ian Evans dheianevans at gmail.com
Mon Oct 23 15:55:56 UTC 2017

On Oct 23, 2017 11:49 AM, "Jay Foster" <jayf0ster at roadrunner.com> wrote:

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.

Good reminder, I've done that in the past.
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