[mythtv] DVB EIT in mythtv-eit

Rudy Zijlstra mythtv at edsons.demon.nl
Thu May 4 08:40:13 UTC 2006


Daniel Kristjansson wrote:

>On Tue, 2006-05-02 at 00:31 +0200, Rudy Zijlstra wrote:
>  
>
>>>On Mon, 2006-05-01 at 22:43 +0200, Janne Grunau wrote:
>>>      
>>>
>>>>No, only NetworkID and TSID together have to be unique. It would be 
>>>>sensible if the TSID in PAT and SDT match. I haven't checked since the 
>>>>SDT monitoring does not to slow down the tuning much.
>>>>        
>>>>
>
>  
>
>>consider the following situation, where the operator is describing all 
>>possible network configurations by sending out all NITs on all TS.
>>See chD444.nit....zip. The relevant SDT is in the sdt capture.
>>In this situation it may be very usefull, at least at TS scan time, to 
>>know which network ID to use. This tells you which of the several NITs 
>>present you should use. This is not uncommon behaviour in cable country. 
>>I strongly suspect that for EIT scanning you also need to know which NIT 
>>to use.
>>    
>>
>
>This info isn't really useful for tuning, but I could for the EIT scan.
>
>However, I think this will all be handled by the EIT caching scheme
>we've been talking about in the last week. Since we will discover
>which transports have most of the EIT information and use that to
>speed up future scans, getting this info from the NIT tables would
>only speed up that first EIT scan where we visit every channel
>without any knowledge of which ones have the most information.
>
>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.
>
>-- Daniel
>  
>
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.
Important 1: only the TS referred to by the NIT with the correct network 
ID will be present on the cable!
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).
Important 3: this means you cannot tune based on SDT info. There is no 
1-1 mapping between SDT and NIT.
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.

Regards,

Rudy


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