[mythtv-users] Caveats in upgrading from Ubuntu 18.04 + MythTV 29.1 to something newer?

Greg Oliver oliver.greg at gmail.com
Tue Apr 25 17:48:07 UTC 2023

On Tue, Apr 25, 2023 at 11:29 AM Stephen Worthington
<stephen_agent at jsw.gen.nz> wrote:
> On Tue, 25 Apr 2023 10:24:28 -0400, you wrote:
> >On 4/24/23 11:59 PM, Stephen Worthington wrote:
> >> I find this interesting, as I am very sensitive to deinterlacing
> >> problems and have not had this happen to me.  I have been using both
> >> VDPAU and NVDEC at times on the 525 drivers and can see no difference
> >> between them, except for the NVDEC drivers supporting more 4K files
> >> than VDPAU, and NVDEC not supporting some older video files.  I do not
> >> remember any difference in the deinterlacing as I moved through the
> >> driver versions from 390 upwards.  I am using Nvidia GT1030 cards.
> >
> >Yeah, I can't rule out that it may be hardware-specific.  In my case
> >it's a GeForce GT 730.  I happened to have a horizontally-panning scene
> >on the TV at the time, and it was distractingly flickering.
> Since a GT730 is obsolete (no longer sold), I doubt that the latest
> drivers get much testing on it.  So it is entirely possible that they
> are broken with respect to a GT730.  So sticking to an older driver
> version that was around when they were still being sold is likely a
> good idea, as the new things in the newer drivers tend to be only for
> the new hardware anyway.  But then eventually you will run into the
> problem that the older drivers will stop being supported and will then
> stop working with the newer kernels.
> Juddering during panning is pretty sure sign the deinterlacing is not
> working properly, but you can get that when using a very crude
> deinterlacing algorithm instead of the best ones.  Which could be a
> configuration problem.  If you want to check the deinterlacing
> actually being used for playback, start playing a problem recording
> and then do M(enu) > Playback > Playback Data.  The information
> displayed at the top of the picture includes a line right at the
> bottom in the middle titled "Deint : " which tells you exactly what is
> being used.  For VDPAU it should say "2 x VDPAU advanced" and for
> NVDEC it should be "2 x NVDEC adaptive".
> Here in New Zealand, it used to be common on the Choice and HGTV
> channels to get recordings with judder during panning, due to the
> setup being used for converting ATSC 29.95 Hz to DVB-T 25 Hz not being
> correct.  They finally fixed that only after Discovery bought those
> channels from the previous owners a couple of years ago.  When I first
> met that, it took me quite a while to discover that no amount of
> fiddling with my deinterlace settings was ever going to be able to fix
> it.
> >Given that the broken-for-reasons-I-didn't-get-around-to-figuring-out
> >6200ch channel changer was the more-pressing deal breaker, I'll admit
> >that I didn't spend a whole lot of time poking around with the
> >deinterlacing issues.  The fact that manually running 6200ch worked fine
> >from a shell, but not as expectd when invoked from MythTV sure was a
> >head scratcher for me.  Could be as simple as a race condition between
> >the channel changing being sent out over firewire and the HD-PVR
> >starting to record.  I did notice that the HD-PVR started recording
> >before 6200ch actually completes (tested via adding e.g. a 10-second
> >sleep to the channel changer).  That's about the point where the time I
> >had sunk into looking at it had exceeded the value of being on a recent
> >Ubuntu version.  :)
> Race conditions are always nasty to deal with.  In this case, there
> has been a recent bug fix in v33 that fixed the problem that
> mythbackend was sometimes generating the pre-recording events at the
> wrong times.  It is possible that the same bug was affecting when the
> channel change command was being run.  If so, that might explain your
> problem.  It would pay to ask the devs exactly when the channel change
> command is supposed to be being run, and check that it is actually
> happening then and not later.  If it is being run at the correct time,
> you could consider running 6200ch from the pre-recording events (now
> that they work properly), as there is a setting that can be used to
> tell mythbackend how much before the recording start it should do the
> first pre-recording event.
> >But after reverting back to my backup that had the 390 Nvidia drivers,
> >it's back to smooth / non-flickering / no evidence of having been
> >interlaced.
> Yes, that is vital to those of us who are bothered by it.  My mother
> does not notice such things.

It is crazy to me how some people do not notice - I have a friend
whose A/V was out of sync by > 300ms and they happily watched TV with
lips and audio off by that much.  It drove me nuts to watch TV over
there until I syned the receiver and firestick..  Just goes to show
how "picky" we can be at times:)

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