[mythtv-users] Ceton vs multirec questions

[Stephen Worthington]

On Wed, 28 Jul 2021 11:34:39 -0400, you wrote:

>    > Date: Wed, 28 Jul 2021 20:24:19 +1200
>    > From: Stephen Worthington <stephen_agent at jsw.gen.nz>
>
>    > This might be as a result of the new "Schedule as a group" option.  If
>    > that is set, as I understand it, it overrides the setting for the
>    > number of multirec tuners and the system will create virtual tuners as
>    > required.  I have never used that option, but I understand it is on by
>    > default in new installs.  You find it in mythtv-setup > Input
>    > connections > select a tuner > Interactions between inputs.
>
>Interesting.  I can find very little about this via a web search:
>  mythtv "schedule as a group"
>returns about three not-very-informative hits.  (Which is surprising,
>since I'd swear I heard about this on the mailing list some time ago,
>and I would have guessed that Google would return those messages.)
>
>However, all six of the real tuners (the first six rows) in my
>cpturecard table do have "schedgroup" set to 1.  (And all of the
>later entries do not.)
>
>If this really does override reclimit, then obviously fiddling with
>that won't matter.  But what does schedgroup buy me?  Overlapping
>(same-"channel", from pre/postroll) recordings sharing a tuner? 
>(Hope so!)
>
>The other reason I'm confused re multiplexes etc is that if I go to the
>web interface for the Ceton, I can clearly see that each channel claims
>a whole bunch of "program" entries, and it's a different list for each
>individual channel.  (Some are mostly in the 1-10 range; some have half
>a dozen entries like 1, 10, 2804, etc.)  My assumption was that these
>were different streams multiplexed on the TS stream arriving for that
>channel---if I record the card "by hand" using its web interface and
>just dump the stream into a file using netcat, things like mpv will
>report that there are are huge numbers of audio and video streams:
>
> (+) Video --vid=1 (mpeg2video 720x480 29.970fps)
>     Video --vid=2 (mpeg2video)
>     Video --vid=3 (mpeg2video)
>     Video --vid=4 (mpeg2video)
>     Video --vid=5 (mpeg2video)
>     [ . . . ]
>     Video --vid=13 (mpeg2video)
>     Video --vid=14 (mpeg2video)
> (+) Audio --aid=1 --alang=eng (ac3 2ch 48000Hz)
>     Audio --aid=2 --alang=spa (ac3 2ch 48000Hz)
>     Audio --aid=3 --alang=eng (ac3)
>     Audio --aid=4 --alang=spa (ac3)
>     [ . . . ]
>     Audio --aid=26 --alang=spa (ac3)
>     Subs  --sid=1 (*) (eia_608)
>
>...though only some of them seem playable with --vid=n.
>
>So I don't know if this implies that there really are multiplexes
>there that Myth can somehow take advantage of, or not.

Schedule as a group does not do anything magical - it can not make the
cablecard do anything new.  So your limitation on tuners working with
a cablecard is the cablecard, which, as I understand it, can only
decode one channel at once.

My experience with encrypted DVB-S(2) channels is that if you scan the
multiplex, you see all the streams for all the channels as the headers
for the channels are not encrypted.  But the data in the streams for
each channel is encrypted.  So unless there are non-encrypted channels
there is no ability to use multirec to record from more than one
channel at once as the cablecard will only decrypt one channel at a
time.

There is one exception to this, which I see with my encrypted IPTV
channels.  If you set an IPTV tuner to normal multirec and tell it
that it has 2 multirec tuners, and then record programmes back to back
with overlapping pre- and post-roll periods, the IPTV tuner will use
the two multirec tuners to record the two separate programs from the
one IPTV stream, rather than using a second (different) IPTV tuner for
the second programme.  I am not sure if this is also possible with
ATSC tuners, which are very like my DVB-T tuners.  My DVB-T tuners if
set with 2 multirec tuners will do that overlap trick where needed,
but they will also record from two different streams on the same
multiplex using the 2 multirec tuners.  If your Ceton tuners try that
with a cablecard it will not work.

What you need for a cablecard is for attached ATSC tuners to be able
to be set to only use multirec for overlapping programmes on the same
channel, and I do not know of any option that does that.