[mythtv] Is there anyone still on list who can give me some help with the channelscan_sm code?

[Karl Dietz]

Hi Roger,

happy new year! Sorry for not being responsive to your DVB-SI work.
I have little hacking time these days :-(

On 31.12.2016 19:03, roger wrote:
> Hi,
>
> I am in the process of rewriting the DVB SI table handling code in
> dvbstreamdata. The objective is to maintain robust in memory caches of
> some of the SI tables. At the moment these are the Service Description
> Table (SDT) and the Event Information Table (EIT). The code uses and
> combination of timestamps and cryptographic hashes to detect version
> wrap around.
>
> The objective of this is that higher level users of dvbstreamdata should
> be able to rely on being passed complete tables not just random segments
> and only when a new version of a table has been received. I am trying to
> avoid the multiple caches of table sections that are currently held in
> various places in the dvb/mpeg code.
>
> The SDT is used in the channel scanning code in channelscan_sm.cpp. Is
> there anyone familiar with this code who can give me a heads up on the
> strategy being used to ensure a that a reaonably complete service (a.k.a
> channel) list is retrieved. Is seems to me at the moment that little
> distinction is being made between "actual" and "other" SDTs. I would
> assume a scanner would use the NIT "other" tables to discover other
> multiplexes and then attempt to grab "actual" SDTs from the new
> multiplex before falling back to using "other" SDTs.

The NIT(a) is the table that contains pointers to all multiplexes of
the network. (maps multiplexes to frequencies) There are also NIT(o)
being broadcast of other networks. Some headends/cable plants are not
able to mark the correct NIT as active/other, so the channel scanner
contains code to mutate between the two based on a property of the
video source. (dvb_nit_id != -1)
That allows old setups to work with MythTV, where one transport is
being fed over satellite with a NIT for DVB-S and multiple NIT for
DVB-C to be put on cable at different cable plants with "dumb"
equipment.

Regards,
Karl