[mythtv-users] Multi-tuner setup

[Michael T. Dean]

On 03/26/2013 01:27 PM, Jeffrey Ratcliffe wrote:
> On 26 March 2013 13:38, Michael T. Dean wrote:
>> Looks like invalid tuning parameters--i.e. due to a bad channel scan.  And,
>> yes, you can have a bad channel scan and invalid tuning information and
>> still get Live TV from the card.  You can use "Delete all video sources" to
> OK. Just out of interest, why wouldn't deleting the channels, and
> rescanning do the trick, then? Or finding the correct parameters
> (how?) and updating that channel manually. Why would scanning again
> produce a different result to the first time? How can I recognise a
> bad scan without waiting for issues like this pop up?
>
> And how can I get Live TV from the card, but not a scheduled recording?
>
> Having said that, I noticed that three hours later, there was MythTV
> managed to record the same channel OK, so I looked at the log and
> found the excerpt below, which talks about successfully using channel
> 52903, which isn't listed by MythTV in the programme guide, although
> in the list of the recordings in MythFrontend, the channel is given as
> the 50903 which failed three hours earlier.
>

For that exact reason--you likely have "garbage" data inside your 
configuration*** (such as "shadow" channels or parts of channel data) 
that's getting pulled up sometimes and not other times.  The best way to 
ensure there's no garbage is to first delete /all/ channel 
configuration, which you do with Delete all video sources.

If you do this--start with a "clean" database, with no channel 
configuration, as you get from Delete all video sources--the only thing 
that determines whether you get a good configuration is whether or not 
you do configuration properly (use the channel scanner properly and at a 
time when the channels are available and with working/properly installed 
and configured tuners and ...).  And since you have to do do the 
configuration properly no matter what, IMHO, starting from a known state 
(clean database) and adding only good information is always better than 
starting from an unknown state and trying to both remove old/bad 
information while adding new good information.  (This is also why when 
someone gives me a text document to format, the first thing I do is 
extract all the text, then format it properly from scratch rather than 
try to undo whatever they've done and format it properly.)

Mike

*** You can get such shadow information if you don't delete things 
properly (i.e. if you're poking around in the database directly) or 
(more commonly) if you scan on top of an old scan and leave old 
information while adding new for those channels that have changed (and 
possibly other ways).  (There may be a way to have a scan clear out old 
stuff--at least in that video source--before putting in new, but I'd 
think we'd have to design it such that it didn't do this by default just 
because some people may have to scan at different times for channels 
that aren't always on.)