[mythtv] 50fps video playback on 30Hz display (4K on HDMI 1.4 output)

[Andreas Mayer]

On Wed, Oct 24, 2018 at 6:17 PM Peter Bennett <pb.mythtv at gmail.com 
<http://lists.mythtv.org/mailman/listinfo/mythtv-dev>> wrote:

> With avsync2 it is almost perfect. Not as good as having the monitor at
> refresh rate 60 but perfectly acceptable.
avsync2 works well, but there are a couple of HD channels on Astra 19.2E 
(720p, ARD, ZDF) where the prebuffer pause does not work anymore when 
using VAAPI with avsync2 (works with VAAPI2/avsync2 and with 
VAAPI/without avsync2), video is not able to catch up even if dropping 
video frames all the time, audio is running with video still picture 
until I'm pressing pause/unpause, after doing this both audio and video 
are fine.
I would like use VAAPI2 with avsync2 for all channels but it looks like 
VAAPI2 is needing more CPU resources than VAAPI at least for HEVC 2160p 
(Astra UHD demo channel) decoding, VAAPI is able to keep up without 
frame drops (at least on a display with 1920x1080 at 60, I think it would 
not be worse on a 3840x2160 at 30 display).
I tried to create a video playback profile with VAAPI for HEVC and 
VAAPI2 for anything else (and avsync2), but it looks like changing 
between those decoders does not work when switching between channels.

> My suggestion is try to get the monitor to refresh rate 50 or 60, or use
> avsync2 (or both). This is the best example of improvement with aysync2
> I have seen.
Yes, I would prefer that too, but currently I have only a mainboard 
(with a Coffee Lake processor) available with HDMI 1.4 (which is limited 
to 3840x2160 at 30, DP would be able to use 3840x2160 at 60).
The other mainboard would have a DP (1.2?) output, but on this mainboard 
there is a Skylake processor installed, which is not able to decode HEVC 
main 10 profile (would need to buy a Kaby Lake for this mainboard to get 
HEVC main 10 decoding support).
And as far as I know there currently is no mainboard available with DP 
1.4 and/or HDMI 2.0b  (even with Intel UHD grapics 630 processors) dor HDR.

> You could change your monitor to run at 1920x1080 at 60fps.
> I am using Display Port for the monitor to get refresh rate 60.
I'm after using 4K (at least as soon as there are more channels 
available), so using 1920x1080 at 60 is not an option for the future (this 
is what I'm currently using).

> You can get HEVC accelerated video with vaapi2, if you use the intel
> display rather than the nvidia. 10bit does not seem to work, at least
> with my system.
You need to have at least a Kaby Lake processor to get HEVC main 10 
decoding support.

> I asked in the developer's irc about adding CUDA/NVDEV support to MythTV
> and the response was not enthusiastic so I put it on the back burner.
> People said they want their VDPAU.
As far as I know VDPAU will probably never be able to provide HEVC main 
10 decoding support because of architectural limitations.

Thank you,
Andreas