[mythtv-users] DVB-T scan error lost me 3 Freeview channels

[D. R. Newman]

Here in the UK, the DVB multiplexes change from time to time, as more
parts of the country move off analog TV. So we have to rescan to get the
new channel and multiplex data.

One thing that was not anticipated by the writers of the DVB-T scanning
code in MythTV, is that the broadcasters would give an existing
frequency a new transportid, and stop using the old transportid. So when
I did a scan within MythTV setup, it created new entries in the
dtv_multiplex table, but left the old ones. I ended up with 4 mplexids
covering two frequencies.

Some of the channels broadcast on those multiplexes remained associated
with the old transportids others were updated to use the new
transportids. In my case, Dave ja vu, Community and Sky3+1 remained on
the old transportid. MythTV would schedule recordings on those channels,
but the recordings would be empty (no file), as the old transportids no
longer work.

I fixed this manually, by removing the old entries in the dtv_multiplex
table, and updating the channel table to replace the old mplexids with
the new ones. Then I did a new scan to verify everything was OK. If you
have lost some channels following a DTV service update, you might need
to do the same.

For the developers of the DVB scanning code, they need to take into
account this somewhat illogical behaviour of broadcasters. It is
possible for a given frequency, on the same card or networkid, to have a
new transportid, and the old transportid not to move to another
frequency, but to stop being used (at least on that transmitter - maybe
it is still in use elsewhere, or from a satellite).

Dave Newman