[Spice-devel] Discuss about camera redirection in SPICE

[zhenwei pi]

On 1/17/22 2:29 PM, Gerd Hoffmann wrote:
>    Hi,
> 
>> Camera redirection through the USB redirection protocol seems feasible. But
>> I have several concerns:
>> 1, UVC started to support H.264 and VP8 since version 1.5, old version OS
>> has no support(Link https://en.wikipedia.org/wiki/USB_video_device_class).
>>
>> 2, Even guest side supports UVC 1.5, the camera App still has a chance to
>> select which format to use. We can control this from hypervisor side.
> 
> The camera could offer vp8 as only supported codec ...
> 
> But, yes, using usb redirection will loose some flexibility because you
> can't recode the video frames then.
> 
>> 3, I noticed that USB emulation uses a lot of CPU, so I also have a plan to
>> introduce virtio camera to reduce the CPU utilization.
> 
> uhci and ehci are pretty bad indeed.  xhci should behave noticeable better.
> 
>> So from the point of my view, I prefer a common camera redirection
>> protocol(event a hard work to do, but I can support it for a long time).
> 
> I think you can take some ideas from the audio protocol (start/stop
> stream, ...).  Define controls (brighness etc), probably best to follow
> uvc or v4l2 here.  Negotiate video format capabilities, so there is the
> option that server and client agree on some future codec when supported
> on both ends.
> 
> take care,
>    Gerd
>


Hi,

Actually, during I developed the QEMU camera subsystem and UVC 
emulation, I referred to both UVC and v4l2.

Detailed type definition and function declaration in 
include/camera/camera.h of this patch:
https://patchwork.kernel.org/project/qemu-devel/patch/20211227142734.691900-2-pizhenwei@bytedance.com/

I suppose the API may looks like this(of cause, detailed implementation 
  needs take some ideas from audio). Could you please take a look at it?

-- 
zhenwei pi