[linux-dvb] DVB file formats

Andrew de Quincey adq_dvb at lidskialf.net
Fri Jun 17 02:38:27 CEST 2005


On Friday 17 June 2005 00:55, Felix Domke wrote:
> Andrew de Quincey wrote:
> >>>[Presets]
> >>>Number=ONID:TSID:SID
> >>
> >>I can't think of a better/clearer structure than this - I've put an
> >> example up on the wiki:
> >>http://www.linuxtv.org/wiki/index.php/File_Format_Comparison#Ideas_for_a_
> >>pr esets_file_format
>
> Looks good, so far.
>
> Some people like having their channels renamed. (Yes, this is another
> thing which shouldn't be required, but people insist on doing this,
> because it works for their 100$ el-cheapo receivers who doesn't care
> about real DVB at all..).
>
> So we might need additional service attributes, to rename a channel. It
> could be useful to have a service under different names in different
> presets.
>
> Sorry, I know that this is a stupid feature, but endusers resist on it.
> We should at least make an optional additional attribute, maybe we could
> keep this as generic as possible, for example to assign special stuff
> (icons, volume presets, ...) per service.
>
> It has to be decided where this data has to be stored, for example in
> either the presets data or seperated...

I somehow suspected this might come up :)

I would really quite like to keep that stuff seperate from the actual 
multiplex/channel definitions... its the sort of thing you'd want to share 
between people when you share preset files. It seems to fit with the presets 
better than with the technical multiplex/channel lists. Especially if we want 
to have them different for different entries.

I've updated the preset ideas in the wiki with a suggestion. Its not as clear 
as it was before unfortunately, but its the best I can think of just now. Let 
me know thoughts/suggestions!

> >>Now however, the multiplex differentiators are the problem (for
> >>distinguishing between transponders with the same IDs). Does anyone have
> >>any suggestions as to good numbers to use?
> >>Obviously they have to be based on the frequency somehow, but they also
> >>have to take into account tuning varaiations between people's systems
> >> (e.g. different LNB drifts).
> >>The first thing that springs to my mind is something like the following:
> >>DVBS: ((frequency / (symbolrate/1000)) << 1) | polarisation
> >>DVBT: (frequency / bandwidth)
> >>DVBC: (frequency / symbolrate)
>
> Looks good.
>
> I don't think it's possible to find a real solution here. The
> user-selected frequency can always be on a "border" to the next id.
> However, i think that only a few channels need this stuff. If presets
> don't work on these few channels, it won't ruin everything.
>
> (Sure, if we find a better way, this would be far better).

Relieved to hear you say that actually - I don't know much about signal 
theory :)




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