[mythtv-users] need help with station rescan after frequency change

Thu Jul 2 16:09:51 UTC 2020

On Thu, 2 Jul 2020 at 17:17, DaveD <mythtv at guiplot.com> wrote:

> On 6/30/20 8:01 AM, Jim Abernathy wrote:
> >
> > On 6/30/20 8:32 AM, Jim Abernathy wrote:
> >>
> >> On 6/30/20 7:31 AM, James Abernathy wrote:
> >>> Last year all but one of my local OTA TV stations changed
> >>> frequencies as a part of the FCC repacking of the USA OTA channels.
> >>>
> >>> Today the last one switched.   I can't remember exactly what I did
> >>> last year, but I remember it was simple. I tried on my
> >>> development v31 FE/BE combo to make sure I had it right before I did
> >>> anything with my production backend.
> >>>
> >>> I failed on the initial test.  All I did was use mythtv-setup and in
> >>> the input connections I did a scan and updated all channels. I still
> >>> could not receive the channel that moved.
> >>>
> >>> 1. Do I have to reconfigure XMLTV?  I use tv_grab_zz_sdjson-sqlite.
> >>> The channel that moved is still called the same thing.
> >>> 2. I have a mixture of HDHR and Hauppauge WinTV Quad PCIe tuners
> >>>
> >>> Jim A
> >>> BTW I did the rescan on a real TV and it found the new channel
> >>
> >> Okay, I think I have this figured out.  I do not know if this is the
> >> optimal solution, but it worked.
> >>
> >> First I used mythtv-setup -> Edit Channels and deleted all channels
> >> from Video Source 'SD'. Then I re-scanned.
> >>
> >> I noticed that when that was done I had a lot of new unwanted
> >> channels so I marked them invisible.  I also noticed that my channel
> >> that moved overnight now had the changed freq. from 11 to 9 which is
> >> correct.  However the XMLTV ID was now blank.
> >>
> >> So I ran as user 'mythtv':
> >>
> >> tv_grab_zz_sdjson_sqlite --manage-lineups --config-file
> >> $HOME/.mythtv/SD.xmltv
> >>
> >> Then did option 5 to manually select the channels. That exercise was
> >> mostly to confirm what I already had.
> >>
> >> When I exited, I did mythfilldatabase, then exited user mythtv and
> >> back in mythtv-setup I found my changed channel had the XMLTV ID.
> >>
> >> Next I started mythbackend up and everything is now work.
> >>
> >> I have no idea what the right steps are but this worked for me.
> >>
> >> Jim A
> >
> > I think I added a step that was not needed. So here is what I think is
> > required at least on a RPi4 v31 with HDHomerun Quatro.
> >
> > 1. Run mythtv-setup which shuts down the backend.
> >
> > 2. in Edit channels, I deleted all the channels on the Video Source in
> > question. SD for me.
> >
> > 3. Run the scan and add all the channels and then edited channels I
> > didn't want to see.
> >
> > 4. Save and exit, which starts the backend.
> >
> > 5. At least on the RPi4, mythfilldatabase is triggered by just
> > starting mythbackend so I just waited.
> >
> > At this point I could view the new channel.
> >
> > Jim A
>
> Seems like a BOATLOAD of work, just to change the frequency on ONE
> CHANNEL!  This is, IMHO, is the weakest part of MythTV (which I love,
> BTW, or I wouldn't waste so much time trying to get it just right!).  I
> have tried figuring out the schema used for channels so I can manually
> control them but I have still not figured it out.  I have ONE channel I
> would like to add and I have come close (I think), but it still would
> not tune in MythTV.
>
> I wrote a GUI QT app based on the source from dvb-apps that lets me use
> scandvb to see what I can get on different days and different antenna
> placement, then optimize the antenna placement for which channels I care
> about.  I have done all my analysis using this app and have a good
> understanding of what is possible and am getting good results in my
> recordings.  But all this analysis revealed ONE channel that mythtv
> didn't see in the latest scan (different frequency?  bad weather?
> Irrelevant!) and now I have to go through all that messing around with
> xmltv IDs and visible and recording rules and channel numbers, etc, etc,
> etc, using what seems like very limited tools (channel editors) to do it
> (back up the DB first!).  Where is the Wiki article about how to
> manually add a channel?
>
> Everything I can find tells me to run a scan, which seems to destroy
> everything I have set up so far.  I have tried backing up the DB, run a
> scan, then save the new DB and compare changes, but there are too many
> differences and I don't understand the inter-relations of the tables.  I
> tried the following:
>
> insert into dtv_multiplex set
> mplexid=207,sourceid=6,frequency=473000000,inversion="a",
> updatetimestamp="2020-06-21 21:18:00", etc...
>
> and then
>
> insert into channel set atsc_major_chan=12, atsc_minor_chan=1,
> callsign="KVOS", name="KVOSDT", channum="12-1", etc...
>
> but I don't really know if my field values were valid.
> https://www.mythtv.org/wiki/Channel_table and
> https://www.mythtv.org/wiki/Dtv_multiplex_table were helpful, but not
> thorough enough to know what needed to be entered or if there were any
> more tables involved.  A python script that prompts for parameters would
> be GREAT!  My above-mentioned app only needs frequency, "8VSB" (for
> ATSC), audio PID, video PID and stream ID and it can tune a channel.  It
> seems to me a script that prompts for those, a video source, a channel
> number, a callsign and an XMLTVID would be all one would need, and that
> is what I am trying to write, but have not succeeded... YET!
>
> Dave D.
>
>
> Hi Dave,

The channel scanning process is now, since v31, documented in the Wiki in
https://www.mythtv.org/wiki/Channel_Scanning
If you nowadays do a scan of any kind, then the existing channel numbers,
channel names, visibility and XMLTV information are all preserved.
Only if you delete the channels before doing a scan then all the XMLTV info
is of course gone.
Adding individual channels manually is not supported mainly because the
idea is that any channel that can be used to make recordings can be found
by a mythtv-setup channel scan.
Also this is a very error-prone process.
I could, and probably will at some point in time, restore the once-present
functionality of importing scan results from other utilities such as
dvbv5-scan. However, the priority is to make the channel scanning in
mythtv-setup so good that you do not need other utilities.

If you want to check what a completely new channel scan would bring then
you can do the following:
- create new Video Source
- connect your capture card (tuner) to the new Video Source
- do a channel scan for the new Video Source
This will not destroy your existing collection of channels.
After experimenting you can connect the capture card back to the original
Video Source and then you are back to using that. Or you can keep on using
the new Video Source.
Note that in the program guide you will see only the channels from video
sources that do have a capture card.

Hope this helps!
Klaas.
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