[linux-dvb] DVB file formats

Robert Schlabbach robert_s at gmx.net
Thu Jun 16 02:58:35 CEST 2005

From: "Andrew de Quincey" <adq_dvb at lidskialf.net>
> In the current format, you would just create more than one [transponder]
> section. [channel]s simply belong to the most recent [transponder] seen.

Why not merge channels (I'd prefer the DVB term "services") and transponder
(locator) information in one section then...? Might be better to keep them
together anyway.

> I don't want to impose restrictions like that - for my purposes, putting
> all types of transponders together in one file is exactly what I want to
> do. As for the type of locator/transponder, in each [transponder]
> the dvbs=, dvbt=, dvbc=, etc key tells you what type of transponder it

I don't like the idea of having a "variable" on the left side of the
equation sign. IMHO, a line like "type=dvbc[;tuning parameters]" would be
better, as an application parsing them could easier find out that it does
not know/want a specific locator/transponder, rather than having to parse
through all values to see if it finds any it recognizes. Using the "type="
style allows the parsing application to tell unknown locator/transponder
types from _corrupted_ sections.

> I agree it would be good to use the DVB specified ONID/TSID. However,
> I am not using that on purpose because I have found several instances
> of transponders with what appear to be "default" settings for these
> values.. i.e. the IDs are the _same_ as on other transponders.

If you merge locator/transponder and service data in one section, that'd be

> I'm sure I remember seeing a transponder where all the channels
> had the same service_id as well :(

No, that's not possible. The service_id references the program_number in
the PAT, and if they all had the same service_id, they'd all point to the
same PAT entry, and thus to the same PMT, i.e. be all exactly the same

> Aha, a presets file is something I hadn't considered.
> I'd definitely want to keep it seperate from the other files though.

Then you have to find a way to satisfactorily reference services. DVB's
ONID:TSID:SID may not be sufficient, as e.g. here in Germany, ASTRA
satellite transponders are fed into the cable networks with exactly the
same ONID:TSID:SID's, so a preset file using only that would not allow
selecting whether the service is to be received from cable or from
satellite (if both are available)... OTOH, services might move and their
ONID:TSID:SID might change, but it will still be the same service. For such
cases, referencing the service name would be better, but some service names
can be found several times, e.g. I think there are a couple "Bloomberg"'s
on ASTRA 19.2°E... Maybe the presets file should contain ONID:TSID:SID
_and_ service name (and maybe network and provider name) and even the
adapter ID, so that the application can then look for the closest match.

FWIW, I think most set-top-boxes simply copy the entire locator/transponder
data into the preset storage, which results in them retaining stale data
even if the scan finds the updated ones. Using a smart referential approach
would fix this...

Robert Schlabbach
e-mail: robert_s at gmx.net
Berlin, Germany

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