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

Michael T. Dean mtdean at thirdcontact.com
Sat Jun 4 14:38:00 UTC 2011


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 .

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

Mike


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