[mythtv-users] Stutter playback 720 60fps

Tue Nov 8 15:17:35 UTC 2016

On Mon, Nov 7, 2016 at 10:39 PM, Stephen Worthington <
stephen_agent at jsw.gen.nz> wrote:

> On Mon, 7 Nov 2016 20:22:07 -0800, you wrote:
>
> >On Mon, Nov 7, 2016 at 8:15 PM, Kevin Johnson <iitywygms at gmail.com>
> wrote:
> >
> >> Hi All:
> >>
> >> Still chasing bugs.
> >>
> >> Recently upgraded from 14.04 to 16.04
> >> Myth went from .27 to .28
> >>
> >> Im running the latest from the mythbuntu repos.
> >>
> >> Sometimes, but not always, when I start live tv the video will stagger.
> >> The audio is fine.
> >> If I pause everything is fine afterwards.  This only happens on 720 p
> >> channels from what I have seen.
> >>
> >> This is what I get in the frontend log.
> >>
> >> Nov  7 20:08:14 g430 mythfrontend.real: mythfrontend[11510]: I
> CoreContext
> >> jitterometer.cpp:120 (RecordEndTime) Player(1): FPS:   58.98 Mean: 16955
> >> Std.Dev: 16741 CPUs: 6% 31% 8% 2%
> >>
> >> Once I hit pause the above message stops repeating.
> >>
> >> Anyone else see this?  Suggestions for a fix?
> >>
> >> Thanks.
> >>
> >
> >Please disregard the above message from logs.  I had the playback info
> >screen up and that was kicking out that message.
> >
> >So I really dont see anything in the logs.
> >
> >What the playback info screen showed is A/V sync:-3.5
> >Until I hit pause then play.  Then it goes to less that 1
>
> It is likely that this is just that the playback is starting too early
> and there is not enough data in the buffers for either the audio or
> the video stream that is being played.  So mythfrontend has to wait
> for more data to arrive for the stream that has run out of data in its
> buffers.  Different broadcasters use different offsets between the
> start of audio and the start of video in their transmissions, and also
> the interleaving size - how much audio or video is transmitted at once
> before switching to transmitting the other stream.  The MythTV
> developers have adjusted how mythfrontend starts to delay the start of
> playing until there is supposed to be enough of both streams in the
> buffers that neither will run out before more data arrives from the
> programme being received.  But they can only work from the data they
> have about what settings the broadcasters are using, and they seem to
> have got it wrong for your part of the world.  Or more likely, your
> broadcasters have got it wrong.  The solution is simple, as you have
> discovered: just pause the playback for a moment.  That lets
> mythbackend buffer more of the data, so mythfrontend will not run out
> of data again.  The devs could adjust the standard setting for how
> long MythTV waits to let the buffers build up before starting
> playback, but increasing that number means that in places where a
> bigger number is not needed, there is more delay between the playback
> of live TV and real time.  There is already a second or two of delay.
>
> The reason that it is happening to you now when it did not on 0.27 is
> likely that the devs have changed the startup delay to be a little
> smaller, for some reason.  But it could be coincidental - maybe your
> broadcasters have just recently typoed one of the settings they use
> for 720p broadcasts.  Or upgraded their broadcast equipment to
> something new that uses different settings.  Or maybe they have added
> extra audio streams (for example, 5.1 audio as well as stereo audio).
> Adding an extra stream means that there is more data to be received
> between arrivals of packets of data for the other streams, so it
> delays other streams a little.
>
> I used to see this problem when I first started using MythTV with
> DVB-T instead of analogue PAL TV transmissions, but it went away after
> the devs changed the startup delay, and has not been back since.  So
> the setting used seems fine for DVB-T and DVB-S/S2 transmissions here
> in New Zealand.
>

Thank you for the info.
It must be a change with mythtv because it happens on multiple frontends.
I do not see this if using Kodi.

It would be nice, (says the guy who know nothing about coding) if this
variable could be adjusted.
I tried adjusting the ringbuffer on the backend, but that made no
difference as I think it is not really used anymore?

Sometimes it will clear itself up after 5 or 10 seconds.  Sometimes it
never stops.
Pausing the playback works, but that is not great when channel surfing.

I tried the extra audiobuffer and that did not make a difference.

Any other suggestions?
Can I delay the playback startup?

> _______________________________________________
> mythtv-users mailing list
> mythtv-users at mythtv.org
> http://lists.mythtv.org/mailman/listinfo/mythtv-users
> http://wiki.mythtv.org/Mailing_List_etiquette
> MythTV Forums: https://forum.mythtv.org
>
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://lists.mythtv.org/pipermail/mythtv-users/attachments/20161108/52966795/attachment.html>