[mythtv-users] Silly question about live tv and two tuners

Ronald Frazier ron at ronfrazier.net
Wed Aug 17 15:41:14 UTC 2011

On Wed, Aug 17, 2011 at 8:29 AM, Martin Moores <moores.martin at gmail.com> wrote:
> Interesting.  I remember reading on this list about adding tuners first,
> then virtual tuners afterwards, as Nick mentioned.  But the Wiki does indeed
> suggest otherwise and the way it describes makes sense.

If you only set it to 2 simultaneous recordings, then the physicals
first/virtuals after setup makes sense. In the link I posted above,
note the 3rd paragraph where it talks about live TV. If you setup your
tuners in the following order

Tuner 1 - Physical
Tuner 1 - Virtual
Tuner 2 - Physical
Tuner 2 - Virtual

the problem would be that if you enabled the "avoid conflicts in live
tv" setting, and if you have 2 frontends watching live tv at the same
time, then each machine is going to default to one of the last 2
tuners, and they will end up sharing a physical tuner. If you order
them as follows:

Tuner 1 - Physical
Tuner 2 - Physical
Tuner 1 - Virtual
Tuner 2 - Virtual

Then you solve the live tv issue, but now you introduce the problem
that myth won't try to use the virtual tuner for the 2nd recording.
The better way to set it up would be

Tuner 1 - Physical
Tuner 1 - Virtual 1
Tuner 2 - Physical
Tuner 2 - Virtual 1
Tuner 1 - Virtual 2
Tuner 2 - Virtual 2

This way, when recording, myth will always try to grab a tuner that's
already tuned to the same multiplex (when possible), and live TV will
always try to grab a tuner that's not used by another livetv session.

> Would also explain
> why my system has never seems to use multirecord yet and doesn't often
> record the 5 minutes soft padding either side of my recordings, maybe
> anyway!

If you mean that it doesn't do the soft padding when another recording
is scheduled before/after it, that's has nothing to do with the
multirec configuration. By default, myth wants to use the lowest
number tuner possible, and it will sacrifice soft padding to do it.
Somewhere there is a box you can check to tell myth to avoid back to
back recordings (though I don't recall if it's worded that way). This
will tell myth to attempt to keep the soft padding in place by
grabbing the next available tuner. So for the 2nd recording, it will
grab the virtual tuner instead of cutting off the physical tuner
before the soft padding is completed. The potential downside of doing
this is that, if you have recordings in progress on your physical AND
virtual tuners, myth will then attempt to use the next physical tuner
rather than cut off one of the others before it has completed the soft
padding. As a result, myth may end up using both tuners and create
problems for live TV. The best way around this is just to make sure
you configured more virtual tuners than you would ever record at once.

In an ideal world, the scheduler would be rewritten to be more
intelligent about handling multirec capable tuners, but I'm sure
that's a pretty huge task and it was just a lot easier to wedge them
into the existing framework the way they are (and thus we end up with
these sort of limitations)

Ron Frazier

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