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

Peter Bennett pb.mythtv at gmail.com
Tue Nov 6 23:40:39 UTC 2018



On 11/6/18 4:25 PM, Andreas Mayer wrote:
> On Wed, 31 Oct 2018 15:26:46, Peter Bennet wrote:
>
>> I tried your sample video and I see the same thing. VAAPI2 performs 
>> very poorly. In fact, it plays way better using software decoding 
>> (opengl slim with number of cpus increased to 4). Something strange 
>> is happening with VAAPI2. I will look into that.
>
> I tried your last commit (ticket 13345) today and the results for 
> VAAPI2 are much better than before (but still worse than for VAAPI)
> I'm using a Gigabyte Z370M-D3H mainboard with a i3-8100 quad core 
> processor and 8GB memory for testing.
>
> VAAPI2:
> top: mythfrontend 80%
> intel_gpu_top: render busy 50%, GAM 75%, CS 50%, TSG 40%, VFE 35%, 
> GAFS 20%
>
> VAAPI:
> top: mythfrontend 45%
> intel_gpu_top: render busy 90%, GAM 97%, CS 90%, GAFS 12%
>
>> Another thing is that probably MythTV is losing some color 
>> information. It is converting 10 bit color to 8 bit color. There 
>> needs to be some change in the OpenGL codes that displays it, to 
>> support the 10 bit color. I believe I can see a difference in colors 
>> between playing the video with VLC and playing it with MythTV. I 
>> don't know what it takes to support 10bit color with openGL.
> I'm still unsure if the Intel driver for Linux currently supports 
> 10bpc, although it looks like there are some changes in Mesa to 
> support 10bpc.
> https://www.intel.com/content/dam/www/public/us/en/documents/white-papers/deep-color-support-graphics-paper.pdf 
>
> https://www.phoronix.com/scan.php?page=news_item&px=Mesa-Lands-10-bit-Color 
>
> Until now I was not able to get an Opengl test program working with 
> 10bpc.
> Gigabyte mainboard with i3-8100 has only HDMI 1.4 output (limited to 
> 4K at 30), my LG TV supports "HDMI UHD Deep Color" only at 4k at 50-60 with 
> YCbCr 4:2:0 or 4:2:2)
> Tried an Asus mainboard with i5-6600 (no HEVC main 10 decoding) and 
> external DP to HDMI 2.0b converter and Nvidia GT 1030(Pascal) card 
> installed (DP 1.4 and HDMI 2.0b output, no Linux VDPAU decoding 
> support for HEVC main 10), but had no success until now.
> https://www.nvidia.com/docs/IO/40049/TB-04701-001_v02_new.pdf
>
> Thank you,
> Andreas
>
I have another change that I am testing, which provides further 
improvement. At last, with this change I can play your sample on my 
laptop and the video keeps up with the audio, there is no stuttering. 
VAAPI2 is still using more CPU than VAAPI, but with baby steps I am 
getting closer. I will commit this one after doing some more testing to 
make sure it does not break anything.

Peter


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