[mythtv] Jumpy video playback

[Klaas de Waal]

On Sat, 11 Jan 2020 at 01:18, Peter Bennett <pb.mythtv at gmail.com> wrote:

>
>
> On 1/9/20 5:36 PM, Klaas de Waal wrote:
> > Hi Mark,
> >
> > My MythTV production system recorded this weekend a program that does
> > not play back correct on my frontend with the Nvidia GT520  (driver
> > version 340).
> > It looks to me that the frame ordering is not correct; it jumps every
> second.
> > The complete recording of 10GB has this when played to the end.
> > However, if I cut off the first GB or so from the file then what
> > remains plays perfect.
> > Also, when I play it back on my development system (Intel only) then
> > the playback is smooth.
> > If you are interested then I can send you the file (or the first 100MB
> of it).
> > Please let me know and also how you want it (WeTransfer or gmail
> > attachment is what I use most of the time).
> >
> > Groetjes,
> > Klaas.
> > _______________________________________________
> >
>
> I have noticed this type of behavior, but only on some reruns of
> Midsomer Murders from early 2000's. It is especially bad on the
> "Ovation" channel. I suspect some issue with the source, particularly
> since I saw similar things when watching Midsomer Murders on Amazon
> Prime with the prime app on NVidia Shield.
>
>
> Peter
> _______________________________________________
>
> I got a bit further on this; the problem is in the frame rate!
It looks like that the recording is incorrectly identified as 24Hz instead
of as 50Hz.

When everything is OK it works like this as I understand it:
(1) Broadcast signal is 50Hz interlaced
(2) The playback info box shows this as 25.00fps
(3) De-interlacing then generates 50 fps.
(4) The Nvidia driver is set to 50Hz by MythTV/xrandr
(5) This is shown in the System Status / Display box (very useful new
addition)
(6) The actual framerate is also shown on my TV as 50Hz

With the problematic recording steps (1) to (3) are the same.
The difference is:
(4) The Nvidia driver is set to 23.98Hz by MythTV/xrandr
(5) This is shown in the System Status / Display box (very useful new
addition)
(6) The actual framerate is also shown on my TV as 50Hz

When the first 10 megabytes of the recording are removed then the playback
is correct.

This happened twice in the last two weeks in about 100 recordings or so.
The broken recording is created with multirec; the previous recording on
that
channel was still running at the moment the new recording started.
I have also in the past observed that the start of playback of recordings
created
by multirec has sometimes blocks.

My tentative conclusion at this moment is:
- there is something not correct in the first 10MB of the file
- the frame rate is obtained from the first 10MB of the file
- this frame rate is used to set the Nvidia with xrandr
- later the correct frame rate is obtained as shown in the playback box
- but the Nvidia framerate setting is never updated

Klaas.
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