[mythtv-users] padding question

glen glenb at glenb.us
Thu Dec 7 04:05:28 UTC 2017


On Thu, 2017-12-07 at 16:50 +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.
> 
> 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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i 
thanks for the reply. again i have no padding set, preroll or postroll
on any of the rules themselves or in the setup/video/general/advanced.
they are all zero. i still don't understand given what you are saying
why the earlier show would run over. i have not changed anything in the
setup of tuners / mulitrecs since i set it up years ago, and it never
did this before. it changed somewhere in an update at .28. on the ota,
it is rare that i would want to record off of a single channel with sub
channels as the quality and content of those subs is not what i am
usually recording, i set it at two as that is the most i have ever
needed. this is not qam, this is ota channels. i appreciate the
explanation. but still don't understand why with no front or back
padding the earlier shows on only the same channel are running over.
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