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

[Diego Viola]

On Sat, Dec 12, 2020 at 1:28 PM Diego Viola <diego.viola@gmail.com> wrote:
>
> 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

OK, I just noticed that it's mostly at the beginning (when I first run
mpv) that the video is jerky/choppy, looks like mpv is still buffering
at that stage, after buffering gets to 99% the video is smoother (with
xhci).

Now I don't understand why buffering with ehci happens a lot faster/smoother.

Nevermind, not an issue after all.

Diego