On 10/03/2025 17.51, Alex Bennée wrote:
David Milosevic <david.milose...@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?
Supported backends: - Video4Linux (V4L2) - GStreamer - libcamera == Example: V4L2 Backend Once implemented, a typical QEMU command line for using a V4L2 backend would look like this ./build/qemu-system-x86_64 \ -device qemu-xhci \ -videodev v4l2,id=cam0,device=/dev/video0 \
Just a quick comment here: QEMU tries often to avoid to introduce new top-level command line switches nowadays. Would it be possible to use "-object" for this instead, like it is e.g. done with the memory backends or rng backends?
Thomas
-device usb-video,videodev=cam0 This sets up a UVC emulated device in the guest, using /dev/video0 from the host via the V4L2 backend. == Next Steps We welcome feedback on design considerations and integration approaches. Let us know if there are existing discussions or preferred directions for this work. Best regards, David Milosevic Firmware Developer 9elements
