[mythtv-users] USA OTA FCC frequency rescan?

James Abernathy jfabernathy at gmail.com
Mon Aug 12 21:21:50 UTC 2019

On Aug 12, 2019, at 10:45 AM, Tom Dexter <digitalaudiorock at gmail.com> wrote:
> 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 rechecked my instructions I created when the system was built and you are correct the Scan is done inside Mythtv-setup and no the XMLTV setup.

My issues were that the rescan found something new or changed that didn’t agree with the XMLTV data it was keying off of.  So my recordings all have the wrong channel name and my Record rules where screwed up where “Only this Channel” was selected.

> 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.

This sounds like what I experienced.

> 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.
> Tom

Sounds like I need to run some test cases and relook at how I edited the call signs last time.

Jim A

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