[mythtv-users] Channel scan to add new channel not working

Stephen Worthington stephen_agent at jsw.gen.nz
Sun Jul 21 08:31:08 UTC 2019

On Sun, 21 Jul 2019 12:31:14 +1000, you wrote:

>However, it didn't actually find the new channel so that's another mystery.
>Any ideas why it wouldn't find the new channel that my TV effortlessly
>added to its line up after a channel scan 20 minutes earlier?

Your TV likely has scanning software that will track the messages that
get transmitted about new channels.  If the broadcaster wants to, they
can send messages on existing multiplexes that tell tuners which other
multiplexes to look on, so a new channel on a new multiplex, or the
moving of old channels to a new multiplex will then work because the
tuner will scan the new multiplex as well as the old ones.  I do not
think that MythTV does that.  I believe that ability may be coming in
v31 though.

Here in New Zealand, as long as you leave your Freeview Certified
device (TV or recording device) on or in standby, it will
automatically receive messages like that and will automatically do any
retuning for channel updates or new channels.  So when you wake up
your TV out of standby, the new channel setup will be there without
you having to do anything.  And if you turn your device completely
off, to get any updates, you just tell it to do an auto scan and all
the updates are done.  This works well because all our TV broadcasters
belong to the Freeview consortium and all use the same agreed
protocols.  Other parts of the world also work the same way, but in
some places there are no agreed protocols and not all the software
understands all the ways channel change notifications are done.

So, the reason MythTV may not have seen the new channel is that it may
be on a new multiplex (new frequency) that MythTV did not scan.  It
would be best to see if there is information on the net about the
channel to find out if that is the case.  MythTV only scans the
frequencies it has been told are the ones used in your location.
Sometimes the broadcasters start using frequencies that are not on
that list, as they have been allocated more bandwidth to use.  So
MythTV may need an updated list (in a fix version or an upgrade
version) for it to be able to scan that frequency.  If that is the
case, then you need to switch your scan settings to use the table that
gives all the valid frequencies for your TV system (eg all USA ATSC
frequencies).  MythTV has such a table for all the systems it knows

An example from New Zealand is that I am getting my TV from the
Wharite transmitter, so I need to scan the 5 frequencies it broadcasts
on.  But not too long ago, the frequency table that was published for
Wharite only had 4 frequencies on it.  Then the Maori Television
frequencies started to be used, adding a 5th frequency in each New
Zealand transmitter location.  Scanning using the Wharite table did
not find the Maori TV frequency, so until the table was updated, I had
to use the New Zealand frequency table, which made the scans take much
longer as there are about 25 frequencies used in New Zealand in total

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