Slow video output from webcam with qemu-xhci but smooth with usb-ehci

[Diego Viola]

Hi,

I'm experiencing a lot of choppiness in the video output when I pass
through my USB webcam to the guest using qemu-xhci as follows:

qemu-system-x86_64 -enable-kvm -hda arch-zoom.qcow2 -m 4G -vga virtio
-device qemu-xhci,id=xhci -device
usb-host,bus=xhci.0,hostdevice=/dev/bus/usb/002/004

My webcam is:

Bus 002 Device 004: ID 04f2:b449 Chicony Electronics Co., Ltd Integrated Camera

I am using mpv /dev/video0 from the guest.

It works fine if I use usb-ehci instead, e.g.:

qemu-system-x86_64 -enable-kvm -hda arch-zoom.qcow2 -m 4G -vga virtio
-device usb-ehci,id=ehci -device
usb-host,bus=ehci.0,hostdevice=/dev/bus/usb/002/004

In this case, the video output from mpv /dev/video0 is not choppy.

My QEMU version is 5.2.0 -- I am running Arch Linux on the host and guest.

Any ideas please?

Thanks,
Diego