[mythtv-users] UK Crystal Palace OTA reception issue on CH55

Stephen Worthington stephen_agent at jsw.gen.nz
Sat Mar 13 13:33:23 UTC 2021

On Sat, 13 Mar 2021 11:18:33 +0100, you wrote:

>> I'm still on V30; it is possible that the new tuner code may make this
>> task easier, but I'm not
>> holding my breath.
>About channel scanning and duplicate multiplexes, you might give the
>current master (pre-v32) a try.
>This now has an option to automatically remove duplicate multiplexes, based
>on signal strength.
>Also the raw data of each scan is stored in the database; this allows a
>replay of a scan with different scanning options in a few seconds.
>Last but maybe not least, there is a new menu to copy non-scanned data such
>as icon file path and XMLTVID from the old channels into the new channels.
>> At least new stuff seems to prompt for which region/area you want to use
>when it detects two sets of muxes.
>About regions, for satellite (FreeSat) you can now define the region id and
>the bouquet id. This decides then the channel numbering.
>If there exists something similar for DVB-T/T2 I could have a look at it,
>but then I would need a few recent full multiplex recordings plus a pointer
>to where it is described.

I believe that here in New Zealand for DVB-T, the LCN (logical channel
number) is available as part of the MHEG5 EPG data.  But so far I have
not found any free downloadable documentation on the MHEG5 data format
- you have to pay ISO/IEC or ETSI I think, so probably only $100 or
so.  The NZ MHEG5 format is a slightly modified version of the UK
MHEG5 format.

For our Sky TV NZ satellite service, the OpenTV format EPG data
carries LCNs.  In my version of tv_grab_dvb_plus that I modified to
handle the Sky NZ EPG, I have it put the LCN in a comment in channel
entries in the XMLTV file:

<channel id="vibe.sky.co.nz"> <!-- number="6" type="0x19" flags="0xcf"
bouquet="25280" region="0" sid="1041" -->
<channel id="uktv.sky.co.nz"> <!-- number="7" type="0x19" flags="0xef"
bouquet="25282" region="0" sid="1003" -->
        <display-name>BBC UKTV</display-name>

The "number=" field is the LCN, and I believe that when I was
modifying tv_grab_dvb_plus, I did find documentation of where the LCN
was in the EPG data, or it was obvious when I was looking at the debug
output.  The full OpenTV format documentation is also only available
if you pay - you have to take up a membership of the OpenTV
organisation, so it would be very expensive.  But the basic DVB-S EPG
packet formats are able to be downloaded in the DVB Bluebooks.

If I remember correctly, the EPG data uses the sid (service ID) value
to tell which channel it applies to.  So to get the LCNs, you would
need to find the packet carrying the LCN and match it to the sid from
the tuning data.

Of course, the LCNs from different sources can overlap - I add 4000 to
the LCN for my Sky NZ channels so they do not clash with my Freeview
DVB-T channels.

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