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

[Peter Bennett]

On 10/23/18 1:07 PM, Andreas Mayer wrote:
> Hi,
>
> I noticed that playback of videos with 50fps (for example HD 720p) on 
> a display using 30 Hz refresh rate does not work (results in slow 
> motion video with stuttering audio).
> I agree that this sounds like something one does not want to achive 
> anyways, but I recently bought a 4K TV and I am using a mainboard with 
> only HDMI 1.4 output (Intel Coffee Lake processor with no LSPCon for 
> DP to HDMI 2.0 conversion), so I'm currently only able to use a 
> maximum of 3840x2160 at 30 for 4K playback (I'm using VAAPI(2)).
>
> Do you think there would there be an easy way to change mythplayer to 
> allow playback of videos with higher frame rate than the refresh rate 
> of the display (maybe using the new avsync2 code - have not tried that 
> yet), maybe by just dropping video frames if there is another frame 
> that has to be displayed until the next display refresh occurs?
>
> I'm able to reproduce even with 1920x1080 by switching the display 
> rate to 30Hz when watching a 50fps video.
>
> I would own a Nvidia GT1030 card as well (which has DP 1.4 and HDMI 
> 2.0 outputs), but currently there is no HEVC Main 10 hardware 
> accelerated video playback available with Mythtv for Nvidia (VDPAU has 
> no HEVC Main 10 support, currently there is no CUDA/NVDEV support 
> available for Mythtv, would be harder work to implent this one).
>
> Any ideas, comments welcome ...
>
> Thank you,
> Andreas
>
>

I set my 4K monitor to refresh rate 30 and played a 60 fps 720p video. 
(I don't know if I have any 50 fps videos). The result is awful. There 
was no audio problem but the picture was alternately slowing and jumping 
ahead. I would get a headache very soon from watching that.  How has 
nobody noticed this before?

I tried vaapi2 and opengl slim for playback profile. Both acted the same 
way. This is not likely to be affected by the playback profile anyway.

With avsync2 it is almost perfect. Not as good as having the monitor at 
refresh rate 60 but perfectly acceptable.

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.

You could change your monitor to run at 1920x1080 at 60fps.

I am using Display Port for the monitor to get refresh rate 60.

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.

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.

Peter