[mythtv] Jumpy video playback

[Mark Kendall]

On Tue, 14 Jan 2020 at 20:54, Klaas de Waal <klaas.de.waal at gmail.com> wrote:
>
> Hi Mark,
>
> File with the first 128MB of the "Jumpy video playback" recording is sent.

Many thanks.

My nvidia box is down at the moment but it plays back fine with all
variations of decoders etc on my main intel dev machine (not using
xrandr).

The problem is this line in the log:-

2020-01-14 22:04:58.228867 I [22455/22591] Decoder
decoders/avformatdecoder.cpp:1363:normalized_fps  AFD: Selected FPS:
23.6667 (Avg:23.6667 Mult:1 Codec:0 Container:90000 Estimated:25)

The initial rate detection is wrong but it is very quickly corrected -
but in the meantime the display mode is switched to support the
incorrect rate.

I'll check the frame rate detection again - but that piece of code is
extremely 'sensitive'.

I can however see that MythVideoOutput won't act on the change in
frame rate if there are no other parameter changes at the same time -
so that can be fixed. Just need to guard against spurious changes as
changing video mode frequently is a recipe for disaster:)

> This corruption does not happen often; the weekend of 4/5 January it happened on two recordings but after that I have not seen it anymore. But this is with a generally rock-solid near-perfection cable signal. There will be more often corrupted files with DVB-T/T2 recordings done with antenna's.

Possibly the same issue as https://code.mythtv.org/trac/ticket/13543 ?

> The way to view the actual display fps is now to stop watching the recording and go to the Information Center / System Status and select the Display tab. The Nvidia driver keeps the last fps setting it has received and hence it is possible to see what it was when playing the video.

With xrandr/mode switching, we always just keep the last video mode as
long as the resolution is the same as the GUI mode - i.e. we assume it
doesn't matter what refresh rate the GUI is using. This saves a lot of
mode switches if you primarily watch 'local' broadcast material -
which will usually be the same frame rate.

> Feature Request: It would be great for debugging if the driver fps value was displayed in the Playback Menu / Playback / Playback Data box. There is already an additional line that shows the Deint settting so there is already space for a "Display fps"  setting to the right of it........

The problem with the debugging screen is it is starting to have a
negative impact on performance - it has gradually got more complicated
and the code to populate the fields is, iirc, not cheap.

I've been mulling over a change to split it into different screens
that you can cycle through with repeated key presses - but that
doesn't work if you bring up the debug screen from the main playback
menu...

As an aside, I always like to use the tv itself to check what refresh
rate it thinks it's using - that has cleared up some confusion on a
number of occasions but not all displays have this functionality.

Thanks and regards
Mark