Re: Re: [RFC] Proposal for a QEMU video subsystem for cameras and webcams

[zhenwei pi]

On 3/11/25 00:57, Thomas Huth wrote:
> On 10/03/2025 17.51, Alex Bennée wrote:
> > David Milosevic <david.milosevic@9elements.com> writes:
> >
> > > Dear QEMU Developers,
> > >
> > > I would like to propose the development of a video subsystem in QEMU, 
> > > with the initial
> > > implementation focusing on UVC video device emulation and support for 
> > > multiple
> > > backends, including V4L2, GStreamer, and libcamera.
> > >
> > > This work is already in progress at 9elements, and we would like to 
> > > upstream it.
> > >
> > > == Motivation
> > >
> > > Currently, USB pass-through is the only way to make video devices 
> > > available to guests, which
> > >
> > >      - excludes non-USB cameras (e.g., MIPI)
> > >      - performs poorly with high-resolution cameras
> > >      - does not work with USB 3.0 video devices (Issue #1613)
> > >
> > > == Proposal
> > >
> > > We aim to introduce a video subsystem in QEMU that allows for the 
> > > implementation of various
> > > video devices, similar to how QEMU handles audio. The first device 
> > > implementation will be
> > > UVC (USB Video Class) device emulation, with support for multiple 
> > > backends. Future extensions
> > > could include virtio-video or other PCI-based video devices.
> >
> > Are you aware of virtio-media? It was an alternative proposal to
> > virtio-video which effectively becomes an encapsulation of v4l to the
> > guest.
>
> ... but USB video would also be nice, wouldn't it? That could enable 
> guests to use webcams without needing additional virtio drivers for it, 
> I think?

Agree. UVC based hardware emulation does not need additional guest 
driver, and it may help guest kernel driver debug. It's also useful for 
USB video related education.

Virtio based hardware will use the common video/camera framework, this 
is also another good shape: hardware devices emulation -> generic 
framework -> multiple backend driver implement.