[mythtv] DVB EIT in mythtv-eit

Janne Grunau janne-mythtv at grunau.be
Thu May 4 14:22:25 UTC 2006

On Thursday 04 May 2006 10:40, Rudy Zijlstra wrote:
> Daniel Kristjansson wrote:
> >On Tue, 2006-05-02 at 00:31 +0200, Rudy Zijlstra wrote:
> >That is, this information could be used to seed information for use
> >during the initial EIT scan, but might not be worth the bother of
> >implementing since we will discover this same information in a more
> >general way during the first EIT scan anyway.
> I think you are forgetting an important use case: the channel scan.
> Also, if you check the information, you will see that several NITs
> are available. These NITs are referring to several TS.

You will see one NIT with table id 0x40 (actual network) and maybe 
several other with table id 0x41 (other networks). Each NIT regardless 
of the table id value will hold one one or more transport descriptors.

> Important 1: only the TS referred to by the NIT with the correct
> network ID will be present on the cable!

Cabel, satellite, terestial transmitter, something like that but it 
doesn't depend on the network id, but the table id matters.

> Important 2: The different network layouts may (and will) overlap.
> Leading to different TS having the same frequency. Of course, only 1
> will actually be present (see 1).

We handle only the NIT with table id 0x40. So this is not a problem at 

> Important 3: this means you cannot tune based on SDT info. There is
> no 1-1 mapping between SDT and NIT.

Of course there is. In the NIT of the actual network each transport is 
specified by original_network_id and transport_stream_id. For every 
combination of this two should exist only one SDT.

> Important 4: The same services will be referenced in different TS.
> (from different NIT). I actuality only 1 NIT is valid, and only 1 TS
> will actually carry the service.

Not a problem, we get the service information from the SDT of the actual 
tuned transport. And there is only one SDT for each actual transport.

I haven't read your previous mail (was it send directly to Daniel?). It 
might be that your cabel provider is incompetent and does not rewrite 
the NITs in the transport streams it provides. But please wait with 
complaints until the channel scanner is working for standard conforming 
DVB networks.


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