[mythtv] [mythtv-commits] Ticket #1866: DVB Scanning - Remaining Issues

Janne Grunau janne-mythtv at grunau.be
Mon Aug 21 17:34:05 UTC 2006

On Monday 21 August 2006 01:23, Rudy Zijlstra wrote:
> Janne Grunau wrote:
> >
> >> Alternatively, full scan is available to find
> >> all the transports being broadcast, which will
> >> work even if the transports do not provide any
> >> information about other transports, as happens
> >> in certain countries.
> >
> > There is no full scan for DVB-S and DVB-C. I don't think that an
> > equivalent to the DVB-T full scan is practical for DVB-S and DVB-C.
> > ... For DVB-C we could scan the appropiate
> > frecency tables we have already. Although it is most of the time
> > more effort than needed.
> For DVB-C using the frequency tables is not a good idea. Most of the
> European cable operators are not adhering  to any frequency table but
> there own. Which may be different for each city.

How do they handle analog channels? I've have never heard something like 
this at least for Germany. I can't remember a single complaint of a 
analog MythTV user (may be caused by my one ignorance). 

> German cable is 
> slowly moving to a 8MHz raster layout. This is also not covered by
> any standard.

Can you name one cable provider that changed from the known frequency 
tables to a 8 Mhz raster? It would make sense for Kabel Deutschland 
since the use DVB-S transponders to transmit the streams from the 
playout center to their local  

> The best way to detect all streams on DVB-C is by a slow frequency
> scan, with 125MHz step size (or 250MHz, depending on tuner
> capability). yes, this takes time. It is the only way though.

You surely meant khz. And it's not the best way. It is maybe the only 
reliable way, but I would consider it as bad. This will take roughly 
6400 tuning attempts (if you know the symbol rate) and is only reliable 
if the hardware can handle offsets smaller than 75 (125) khz (I don't 
know if this within standard tuner/frontend capabilities).

> And please, please, do ignore NIT while you are doing this?? Because 
> many cable operators do not provide a valid NIT-actual. They provide
> many NIT-Other, but no, or no valid NIT-actual.....

This is something I personally don't get. I can understand that a NIT 
becomes invalid after time if nobody maintains it. But I don't see the 
point in transmitting a NIT_other in cable natworks. It isn't a useful 
information at all.
Do the cable providers claim adhering the DVB spec? I.e. can you buy any 
DVB-C STB (with the appropiate crypto system) and use it? Or have you 
to buy or rent a STB from the provider? Are the STBs from the providers 
standard DVB STBs?


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