Spice gstreamer:h264 black screen

Good day! I use QEMU 10.1.1 with libvirt 11.6.0 on Debian Bookworm. I found that in this release it is possible to use hardware encoder to code video stream by using this option to spice according to ui/spice: Enable gl=on option for non-local or remote clients series 376d4b22 So I tested with following lines

-device virtio-vga,max_outputs=1,xres=1920,yres=1080,blob=true

-spice port=3001,gl=on,disable-ticketing=on,video-codecs=gstreamer:h264

and remote-viewer --spice-debug spice://x.x.x.x:3001 on the client side.

Associated Spice server MR (merged):

https://gitlab.freedesktop.org/spice/spice/-/merge_requests/229

I use spice 0.16 and spice-protocol 0.14.5 Qemu launch OK without any errors, But remote-viewer gives me black screen without errors. Maybe I need something more? vainfo gives me all encoders with intel 25 non-free drivers. Thanx in advance Bye.