[mythtv-users] padding question

David Engel david at istwok.net
Thu Dec 7 15:53:21 UTC 2017


On Thu, Dec 07, 2017 at 04:50:21PM +1300, Stephen Worthington wrote:
> On Wed, 06 Dec 2017 19:09:27 -0800, you wrote:
> 
> >beginning somewhere in the updates to .28 i started getting a strange
> >padding issue on my ota recordings. i had 2 hdhomerun dual tuners and
> >just now replaced them with one hdhomerun quattro unit, but the same 4
> >tuners. each set to multirec of 2 per tuner to allow for subchannel and
> >main channel on one tuner. i have no padding set in any recording rule
> >and none set under setup/video/advanced where the option is also
> >provided.
> >
> >what happens is this: if i record a program running from say 8pm-9pm on
> >a channel and then have a program scheduled from 9pm to 10pm on the
> >same channel. the recording of the first goes over around 30 seconds.
> >the second show is correct, unless there is a third show on the same
> >channel to be recorded, then that goes over also. the scheduler will
> >almost always assign a different tuner to the 2nd show. if i have all
> >four tuners being used, it was that there was no padding. now i notice
> >that even with all four being used i still get the padding, this may be
> >only since i switched out to the quatro. I have a feeling that it
> >somehow has to do with multirec, but this is something that never
> >happened for the six years i have been using myth. 
> >
> >if anyone has any ideas how to avoid please let me know. also when i
> >would force the back to back shows on same channel to the same tuner
> >number, it did not happen, but i don't know if that is currently the
> >case. it's not a real big thing, but i would like to correct the
> >behavior if possible. i am running on arch linux, on their current
> >mythtv packages. which is now 29.0-b4e4ddcf97
> >
> >thanks.
> 
> There are two different types of preroll and postroll settings that
> are applied to recordings.  One comes from the recording rule and is
> always applied.  The others come from two global settings: (v29) Setup
> > Video > General > General (Advanced) > Time to record before start
> of show and Time to record after end of show.  These two settings are
> RecordPreRoll and RecordOverTime respectively in the database settings
> table, and I think default to 60 seconds each.  When they are used,
> the preroll and postroll they do is added onto the preroll and
> postroll that is done from the recording rule settings.  However, when
> there are back-to-back recordings on the same multirec tuner, the
> RecordPreRoll and RecordOverTime settings are not used, as that would
> mean that MythTV had to record from the same multitrec tuner to two
> different recordings at once, which it can not do.
> 
> With the preroll and postroll settings from a recording rule, the
> times are used to extend the recording time at both ends and the
> extended recording time is the one used in selecting which multirec
> tuner is free to be used for a recording.  So if those preroll or
> postroll settings mean that the next recording will overlap with one
> that is currently using a multirec tuner, then a different multirec
> tuner will be used for the recording.
> 
> So your setting up of multirec tuners is likely what is causing the
> difference.  MythTV has not changed how it works, but the extra tuners
> available means that it can now use options it was unable to before.

Actually, MythTV has changed.  When there are back to back programs on
the same multiplex, it tries to put them on different multirec inputs
for the same physical input.  That preserves the post-roll for the
earlier show and the pre-roll for the later show.

David

> However, you have only set up two multirec tuners per physical tuner.
> You probably should set up at least five multirec tuners per physical
> tuner, as there are often several channels on the same multiplex that
> you will want to be able to record from at the same time, and it is
> best to use the same physical tuner to record all of them as that
> leaves the other physical tuners free to be used on other multiplexes.
> With only two multirec tuners per physical tuner, two back-to-back
> recordings with overlap due to pre- or postroll will use up both
> multirec tuners, and a recording from another channel on the same
> multiplex will be forced to use another physical tuner.
> 
> The only reason not to have as many multirec tuners as possible per
> physical tuner is that the scheduler can then record many more
> programs at once when they happen to be on the same multiplex, and if
> you do not have enough disk drives it can record too many at once to
> one drive and cause data loss in the recordings due to the disk head
> movement being too slow.
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-- 
David Engel
david at istwok.net


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