[Spice-devel] Stuttering video playback on LAN

Mon Jul 27 07:40:27 UTC 2020

Hi Uri

I've succeeded in using h264 with spice-streaming-agent, but only with a linux client. The windows client does not seem to support anything besides mjpeg, even after installing and tinkering with gstreamer.
I've opened a bugreport: https://gitlab.com/virt-viewer/virt-viewer/-/issues/5

Another drawback: spice-streaming-agent only works with the x264enc encoder, which does not support VAAPI based hardware acceleration with the Intel GPU I passed through with GVT-g.

The vaapih264enc codec claimed that it cannot produce a x-h264 stream:

# ./spice-streaming-agent -d -c gst.h264=vaapih264enc
...
spice-streaming-agent[266317]: Gstreamer plugin: Specified encoder named 'vaapih264enc' cannot produce 'video/x-h264, stream-format=(string)byte-stream, framerate=(fraction)25/1' streams. Make sure that gst.CODEC=ENCODER is correctly specified and that the encoder is available.
spice-streaming-agent[266317]: Gstreamer plugin: 'x264enc' encoder plugin is used

The avenc_h264 codec loaded but failed:

# ./spice-streaming-agent -c gst.h264=avenc_h264_omx:bitrate=100000
spice-streaming-agent[269477]: Gstreamer plugin: Looking for encoder plugins which can produce a 'video/x-h264, stream-format=(string)byte-stream, framerate=(fraction)25/1' stream
spice-streaming-agent[269477]: Gstreamer plugin: 'vaapih264enc' plugin is available
spice-streaming-agent[269477]: Gstreamer plugin: 'x264enc' plugin is available
spice-streaming-agent[269477]: Gstreamer plugin: 'avenc_h264_omx' plugin is available
spice-streaming-agent[269477]: Gstreamer plugin: 'avenc_h264_omx' encoder plugin is used
spice-streaming-agent[269477]: Gstreamer plugin: Trying to set encoder property: 'bitrate = 100000'
** (spice-streaming-agent:269477): CRITICAL **: 22:47:26.612: gst_vaapi_display_lock: assertion 'display != NULL' failed
** (spice-streaming-agent:269477): CRITICAL **: 22:47:26.612: gst_vaapi_display_unlock: assertion 'display != NULL' failed
** (spice-streaming-agent:269477): CRITICAL **: 22:47:26.617: gst_vaapi_display_lock: assertion 'display != NULL' failed
** (spice-streaming-agent:269477): CRITICAL **: 22:47:26.617: gst_vaapi_display_unlock: assertion 'display != NULL' failed
spice-streaming-agent[269477]: No sample- EOS or state change

So I reverted back to using regular spice in qemu without spice-streaming-agent.
I think it would be a huge improvement if the spice component in the qemu host process could leverage GPU based encoding with h264. We wouldn't need a guest agent, we wouldn't require GPU passthrough and have great performance for multimedia use-cases. Not sure were I would open a feature request for that, though.

Best,
Felix

On 18.05.20 12:21, Uri Lublin wrote:
> On 5/17/20 6:35 PM, Felix Leimbach wrote:
>> 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".
>
> Maybe the client is built without gstreamer.

>> 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).
>
> With egl-headless, spice-server encodes the whole screen, not 720x576 video. Since the client
> supports almost no codec likely
> it's using mjpeg
>
>>
>> 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.
>
> Your conclusion makes sense to me.
>
>>
>> Is it possible to GPU-accelerate the video encoding in the host qemu process?
>
> I think it can not use anything other than mjpeg if that's the only codec the client supports.
>
>> I've built spice and qemu with gstreamer and drm support and VA-API is working nicely.
>> Can spice use that? How?
>
> Possibly, for H264 you need to change the get_gst_codec_name (gstreamer pipe);
> For vp8 it should be done already.
>
>>
>>>>
>>>> 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?
>
> Likely.
>
> Uri.
>
>> 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
>>