[Spice-devel] Stuttering video playback on LAN

Sun May 17 15:35:09 UTC 2020

Hi Uri,

On 17.05.20 16:08, Uri Lublin wrote:
> On 5/16/20 7:07 PM, Felix Leimbach wrote:
>>
>>>>
>>>> I experience stuttering video playback in remote-viewer despite connecting
>>>> via GBit/s LAN, using fast hardware and the QXL driver.
>>>> Up until a video size of roughly 800x600 the playback is smooth. But on
>>>> anything bigger, like my native resolution of 2540x1440, video playback is
>>>> stuttering annoyingly.
>>>> After lots of unsuccessful tinkering with spice parameters and qxl parameters
>>>> I'm asking you guys for help.
>>>>
>>>> Client:
>>>> Windows 10 1909
>>>> Remote Viewer 8.0-256
>>>> Quadcore i7-7820HQ 2.9GHz
>>>> 16GB DDR4 RAM
>>>>
>>>> Host of the VM:
>>>> Gentoo Linux
>>>> Kernel 4.14.172
>>>> Qemu 4.2.0
>>
>> I've updated to newer versions in the meantime, but no noticeable changes.
>>
>> Qemu 5.0.0
>> Host kernel 5.4.39
>> Remote Viewer 9.0-256 (x64) on the Windows 10 Client
>>
>>>> <snipped>
>>>>
>
> <snipped>
>
>> I noticed very high CPU usage in the guest during playback, because chrome, vlc, mpv used software h264 decoding.
>> I fixed this by passing a virtualized instance of the hosts Intel GPU to the guest via GVT-g.
>>
>> These are the qemu parameters I use for GVT-g:
>> -spice port=5906,addr=10.42.2.250,password=changed
>> -vga virtio
>> -display egl-headless,rendernode=/dev/dri/card0
>> -device vfio-pci,sysfsdev=/sys/bus/mdev/devices/f14c80d5-9ade-4802-9509-1d877d32d159,display=on,ramfb=on,driver=vfio-pci-nohotplug
>
> Perhaps here it would help to set streaming-video=all -spice option.

It doesn't really help. Still very stuttering playback, even with a video-player window size of only 720x576.
I now believe this is caused by a CPU bottleneck on the CLIENT (not guest), i.e. my Windows 10 machine.
virt-viewer.exe uses consistently 12% CPU, which is 100% of one core (Quad Core with SMT => 8 logical cores).
This is crazy, since the CPU core is running a modern i7 at 3.6 GHz (Turbo) with no other significant CPU users (system is idle).
Could this be a problem of remote-viewer.exe not using gstreamer codecs (and hw accel) properly?
Got these spice-debug messages on the client: "no video decoders from GSTreamer for {mjpeg,vp8,h264,vp9,h265} were found".

Also I noticed that the qemu process on the host is using much CPU, probably due to spice encoding the video frames.
The host shows 4 qemu-ystem-x86_64 threads using 93%, 34%, 24%, 16% CPU when playing a 720x576 video in the guest.
However the guest shows only 14% and 7% use for its 2 vCPUs in htop because it uses VA-API (GPT-g) in the video player (vlc, mpv).

So the host qemu threads use MUCH more CPU than the guest. When I disconnect spice (video still playing) the host qemu CPU usage drops to 35%, 1%, 1%, 1%, as expected.
Conclusion: Spice encoding on the host is very CPU hungry.

Is it possible to GPU-accelerate the video encoding in the host qemu process?
I've built spice and qemu with gstreamer and drm support and VA-API is working nicely.
Can spice use that? How?

>>
>> Unfortunately video playback is still not smoother. In fact it is about the same smoothness but new visual artefacts in the video make it worse. I think this is due to egl-headless.
>> For testing/comparison I installed a Windows 10 guest with the same GVT-g GPU and used RDP with h264 activated. Playback was much better and used only about 120MBit/s.
>>
>> Next I tried using the spice-streaming-agent in the guest to send a h264 encoded picture via spice.
>> However, the windows build of remote-viewer doesn't seem to support this. The new spice display is created and I see the mouse cursor in it but no picture (just black).
>
> You may be the first to test spice-streaming-agent + windows client.
>
> I think there is some work to be done in the windows client to make
> it handle better streams from spice-streaming-agent
>
> Also there is some work to be done to enable spice-streaming-agent
> on windows guests.
>
>> Log from the guest:
>> felix at idefix:~$ ./spice-streaming-agent -d
>> spice-streaming-agent[2465]: GOT START_STOP message -- request to START streaming
>> spice-streaming-agent[2465]: streaming starts now
>> spice-streaming-agent[2465]: Got device info of 1 devices from the plugin
>> spice-streaming-agent[2465]:    stream id 0: device address: pci/0000/06.0, device display id: 2
>> spice-streaming-agent[2465]: got a frame -- size is 321265 (26 ms) (1589641660285 ms from last frame)(1589641660258136 us)
>> spice-streaming-agent[2465]: wXh 1920X1200  codec=1
>
> Note that it's not H264, but MJPEG (codec=1)

You are right, so I debugged this:

Launching spice-streaming-agent with GST_DEBUG=6 shows a bunch of h264 related messages which seem to indicate that the gstreamer codecs are loaded (not sure):
gstregistry.c:461:gst_registry_add_plugin:<registry0> adding plugin 0x55d279f8fe70 for filename "/usr/lib/x86_64-linux-gnu/gstreamer-1.0/libgstuvch264.so"
gstregistry.c:577:gst_registry_add_feature:<registry0> adding feature 0x55d279fe1650 (video/x-h264)
gstregistrychunks.c:729:gst_registry_chunks_load_feature: Added feature vp8enc, plugin 0x55d279ed1150 vpx

However I didn't find an argument to force spice-streaming-agent to use a specific codec. Reading the source code I found the option "-c codec_name=h264", but it doesn't seem to have any effect.

Maybe it fails auto-negotiation with the client which does not support it?
On the client with the "--spice-debug" option I found interesting messages:

(remote-viewer.exe:15956): Spice-DEBUG: 17:17:06.218: ../src/channel-display-gst.c:792:gstvideo_has_codec: No video decoders from GStreamer for mjpeg were found
(remote-viewer.exe:15956): GSpice-DEBUG: 17:17:06.218: ../src/channel-display.c:894 GStreamer does not support the mjpeg codec
(remote-viewer.exe:15956): Spice-DEBUG: 17:17:06.219: ../src/channel-display-gst.c:792:gstvideo_has_codec: No video decoders from GStreamer for vp8 were found
(remote-viewer.exe:15956): GSpice-DEBUG: 17:17:06.220: ../src/channel-display.c:894 GStreamer does not support the vp8 codec
(remote-viewer.exe:15956): Spice-DEBUG: 17:17:06.221: ../src/channel-display-gst.c:792:gstvideo_has_codec: No video decoders from GStreamer for h264 were found
(remote-viewer.exe:15956): GSpice-DEBUG: 17:17:06.222: ../src/channel-display.c:894 GStreamer does not support the h264 codec
(remote-viewer.exe:15956): Spice-DEBUG: 17:17:06.223: ../src/channel-display-gst.c:792:gstvideo_has_codec: No video decoders from GStreamer for vp9 were found
(remote-viewer.exe:15956): GSpice-DEBUG: 17:17:06.224: ../src/channel-display.c:894 GStreamer does not support the vp9 codec
(remote-viewer.exe:15956): Spice-DEBUG: 17:17:06.227: ../src/channel-display-gst.c:792:gstvideo_has_codec: No video decoders from GStreamer for h265 were found
(remote-viewer.exe:15956): GSpice-DEBUG: 17:17:06.230: ../src/channel-display.c:894 GStreamer does not support the h265 codec

Any ideas how to fix this? Should I open a bug report?

>> <snipped>
>>
>> If I use remote viewer from a linux client then it does indeed work! Playback is nearly smooth, about the same as with RDP and h264!
>> So I guess it's a bug in the windows remote-viewer. Seems like it doesn't have gstreamer support, so I'll open a bug report.
>>
>> Any other ideas what I can try to get good reasonable video playback with good office-work performance?
>>
>> On a side note: Audio via spice isn't working. I hear a few strange noises and then only silence. So I use pulseaudio transmitting the sound to the client independent of spice.

Found the reason: It's a regression in the windows version of remote-viewer. Was caused by libgstdirectsound.dll being replaced with libgstwasapi.dll and this changed the audio subsystem being used.
Details: https://gitlab.com/virt-viewer/virt-viewer/-/issues/2

Cheers,
Felix