[mythtv-users] USA OTA FCC frequency rescan?

Tom Dexter digitalaudiorock at gmail.com
Mon Aug 12 14:45:08 UTC 2019

On 8/12/19, James Abernathy <jfabernathy at gmail.com> wrote:
> So my local OTA channels have started the warning about September 6 and
> doing a rescan to continue receiving their channels.
> My backend is mythtv v30 with 2 tuner systems.  One is a PCIe card, the
> HAUPPAUGE WinTV-quadHD PCI Express TV Tuner Card 1609. The other is a
> SiliconDust HDHomerun Quatro.
> I currently get my EPG from SchedulesDirect via
> tv_grab_zz_sdjson_sqlite. The Input Connections for both sets of tuners,
> i.e. 8-tuners, use the same Video Source which is the one setup to use
> tv_grab_zz_sdjson_sqlite.
> Can someone point me to instructions or discussion on what to do in my
> case? I think the rescan is done externally to mythtv-setup using steps
> defined at https://www.mythtv.org/wiki/XMLTV for initial setup, but I
> remember that if not careful you can loose Recording rules and
> previously recorded metadata is some cases.
> Has anyone worked out a way to do the rescan without messing things up??
> Jim A

As far as I can see, anything you're referring to in that XMLTV wiki
don't apply for tuners that require channel scanning. That includes
anything for OTA ATSC channels as you have. Nothing there will address
finding an changing the new frequencies of channels.

I've had enough issues with re-scanning in mythtv-setup that I've
actually written myself some utilities to manually change frequencies
on existing channels...though they're not something that would likely
be safe for anyone else to use. I just got through the major changes
that occurred around here to several major networks on 8/1.

Having said that however, I think you can avoid those issues with the
mythtv-setup rescan IF you're careful regarding one aspect of the
rescan: Changes to the callsign that the broadcaster's may have made.
THAT evil practice on their part is generally responsible for all
issues caused by the rescan. The reason for that is that MythTV can
only associate the new scan with your existing channels based on the
callsign. If the broadcaster changes that, MythTV WILL create a new
channel instead of updating the old one. That's where you start
getting a mess. Years ago I had a rescan where NBC changed the
callsign of their main channel from NBC-DT to just NBC resulting in a
new channel and all sorts of issues.

Others can chime in if I have anything wrong here, but I believe you
can prevent this proactively as follows:

I see you have an HDHomeRun which means you have the hdhomerun_config
utility. After the frequencies change you can scan with that using
this syntax (against any of the tuners on your HDHomeRun):

hdhomerun_config <id> scan <tuner> [<filename>]

...where <id> is the hex id of HDHomeRun and <tuner> is, for example /tuner1.

Then you want to compare that output mainly to see where callsigns may
have changed as compared to those you have on your existing channels
in MythTV. I'm fairly sure that if you use the channel editor to
change the callsigns of any that may have changed to the new callsign
reported in that scan output, you should avoid issues.

Again, others can chime in if I'm missing something.


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