GT 1030 4K video stuttering

Hi all,

I just built a new HTPC with the following config:

- Intel Celeron G3900 @ 2.8 Ghz (dual core, no HT)

- Gigabyte GT1030 (2GB)

- 4GB DDR4-2100 RAM

- 40 GB Intel SSD

I waited a while to buy all components and to install LibreElec because by the time I got my GT1030 LE 8.2 wasn't out yet (with official support for the GT1030). It's hooked up to a Pioneer VSX-830 receiver that has 4K support (and I also have a Samsung 4K TV). LibreElec immediately set its resolution to 3840x2160, so all seemed well.

Now that I'm all up and running I've got a problem with GPU decoding most (all?) of the videos. I first noticed this when playing the 60FPS big buck bunny 4K test file, which is x264 and seems to stutter at some parts (especially at the beginning of the video). I'm aware that 10 bit HEVC is not supported at the moment, but 8 bit HEVC videos are unplayable as well. When I'm playing 1080p TV show content everything is fine, except that my HTPC seems to get rather hot.

Once I enable the CPU load counter I see both CPU cores hovering around 50% at 1080p content and the big buck bunny 4K x264 test file. Once I start playing an 8 bit HEVC 4K movie, both cores go to 100% and audio starts dropping out. Stuttering is also very noticeable.

It's probably the VDPAU not correctly being enabled, but once I turn it off the 4K big buck bunny test file is lagging even more. So VDPAU seems to do something. I also changed double buffering to triple buffering, to no avail.

When I installed my GT 1030 in an Optiplex running Windows 10, it worked fine for all content. I really want to run something Linux based though, and using LibreElec is my preferred choice.

Any clues on where I go from here?

What about NVIDIA NVDEC / CUVID? I read somewhere that this was Nvidia's answer for full HEVC support and that ffmpeg supports this already. Is this coming to Kodi/LibreElec?

I didn't really count on having to use my Intel GPU for decoding and for that I bought a H110 motherboard with Skylake CPU. Didn't you need at least Kaby Lake for full 4k60 support?

Thanks for your quick answer!

Hi, thanks for the replies!

I finally figured it out. It was your screenshot Klojum that pointed me to the right direction.

I noticed near 0% CPU load while you were playing the 8K test video. Whatever video I played, be it 1080p, 4K or something else, it always hovered around 70% CPU usage, but not from Kodi.bin, but Xorg instead. I also noticed this behavior when just sitting in some menus. When I switched the output to 1080p, all was fine. The CPU usage of Xorg immediately went down to near 0% CPU usage.

The problem turned out to be the Pioneer AVR. On the Pioneer Android app I noticed the input video source being sent was YCbCr 4:2:0, even though Kodi was configured to do Full RGB. The BD input on the AVR was not configured to do YCbCr 4:4:4 at 4k60, but 4:2:0 instead. Once I configured the input to do the full 4:4:4, LibreElec started sending me RGB Full video, which was then being converted to YCbCr 4:4:4 as output. Once I did this, the menu and all videos immediately went back to being smooth. CPU usage was around 20% while playing videos. Xorg was probably converting the framebuffer from one colorspace to another, causing the high CPU usage.

I couldn't resist to stop messing around to get it even further down. I ended up modifying my xorg.conf, with the following changes:

Section "Screen"
    Identifier     "screen"
    Device         "nvidia"
    DefaultDepth    24
    Option         "ColorRange" "Full"
    Option         "ColorSpace" "YCbCr444"
    SubSection     "Display"
        Depth       24
    EndSubSection
EndSection

The input source being sent is YCbCr 4:4:4 now, so the AVR isn't converting the signal anymore. Better yet, the CPU usage is now below 10% average.

Thanks for putting me in the right direction guys!