If you choose to enable the video streaming support of gstreamer, please try to install addtional gst-plugins which matching the video codecs One the client side: mjpeg,x264 media-plugins/gst-plugins-libav:1.0 vpx media-plugins/gst-plugins-vpx:1.0 One the server side (which app-emulation/qemu running), you should also install additional gstreamer plugins for the app-emulation/spice package: mjpeg media-plugins/gst-plugins-libav:1.0 vpx media-plugins/gst-plugins-vpx:1.0 x264 media-plugins/gst-plugins-x264:1.0