[mythtv-users] How does mythtv determine tuning frequency?

Jerry Rubinow jerrymr at gmail.com
Sat Jun 4 14:51:08 UTC 2011

On Sat, Jun 4, 2011 at 10:38 AM, Michael T. Dean <mtdean at thirdcontact.com>wrote:

> On 06/04/2011 10:24 AM, Jerry Rubinow wrote:
> > On Sat, Jun 4, 2011 at 10:16 AM, Michael T. Dean wrote:
> >> On 06/04/2011 10:06 AM, Jerry Rubinow wrote:
> >>> Myth suddenly started tuning to the wrong frequencies for my
> >>> HDHomerun.  I wanted to tweak just the few channels I get through the
> >>> HDHR, and I was unable to determine how it gets from the channel entry
> >>> in the "channel" table in the DB to the frequency it uses in the
> >>> channelscan_dtv_multiplex table.
> >>>
> >>> One channel in the channel table, for example, has a mplexid of 101
> >>> and a serviceid of 1143.  I look up the entry
> >>> in channelscan_dtv_multiplex with a transportid of 101.  This has a
> >>> frequency of 645000000.  However, this is not what I see in the
> >>> logfile that myth is tuning to - 513000000.
> >> For digital channels, MythTV uses a starting frequency, then uses the
> >> information specified by tables in the digital stream you receive on
> >> that frequency.  If your frequencies have changed for a digital source,
> >> you really need to rescan.
> > I expect frequency reassignments by the provider are the only thing this
> > could be, since I haven't modified my system recently.
> >
> > Is it advisable to first clear the existing tables somehow?
> >   My  channelscan_dtv_multiplex has over 300 entries in it, and my
> > channelscan_channel table has over 2500.  I should mention my system just
> > has an HDHR and a HD-PVR.
> MythTV will take care of that for you.  However, I tend to like to
> always start channel setup from a known location--completely clean
> setup.  So, for that, I do the video sources portion of
> http://www.gossamer-threads.com/lists/mythtv/users/264034#264034 .

Thanks Mike, that's what I needed to know.

> Also, I highly recommend anyone who messes with MythTV configuration
> back up the DB, first.  Because if you don't remember how to do the
> scanning/configure xmltvids/set up channels/whatever or you make a
> mistake or MythTV crashes on you or whatever, you could then always
> restore the old DB and be no worse off than you are now.
> http://www.mythtv.org/wiki/Database_Backup_and_Restore


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