Fix device_caps error -22 (EINVAL) on Linux 5.4+

[grandchild]

torvalds/linux@3c13505 broke this driver, requiring the video device's
device_caps be set in advance.

Set the same device caps that are reported from vidioc_querycap().

Fixes #7.

[thamma]

Thanks for your contribution. Thanks to you, I can successfully load the driver.

After inserting the module/plugging in the camera, dmesg reports

[  515.585237] gspca_main: kinect2-2.14.0 probing 045e:02c4
[  515.585690] usbcore: registered new interface driver gspca_kinect2

which sounds very good, but when reading the video devices /dev/video0 and /dev/video1 (that are indeed present), I can find these errors in dmesg for which I don't know where they originate from.

[  578.426371] gspca_main: usb_submit_urb() ret -1
[  578.426404] gspca_kinect2 2-8:1.1: urb status: -2
[  578.426407] gspca_main: usb_submit_urb() ret -1
[  578.426443] gspca_kinect2 2-8:1.1: urb status: -2
[  578.426446] gspca_main: usb_submit_urb() ret -1

I'm grateful for any input you can provide on this issue.

[grandchild]

@thamma: I geht the same output, but I can still use the Kinect and get RGB video out.
Is that not the case for you?

[thamma]

Sadly no. I can neither read from /dev/video0 nor from /dev/video1.

Neither mpv (which usually can immediately read from video devices) nor OBS or applications accessing webcams immediately read any data successfully.

Mpv reports

$ mpv /dev/video0
Failed to recognize file format.

Exiting... (Errors when loading file)

I will double check if I loaded all required kernel modules, but I am very certain I always do. I am running my Kinect on rather low amperage (1A instead of 2-3A which some people reccommend), however Protonect (the example program from the libfreenect2 project) can read all video channels as it is supposed to.

[thamma]

Using v4l-utils yields some more info on the devices. In particular, For the Streaming Parameters Video Capture I get 0fps which might lead to further culprits.

$ v4l2-ctl --list-devices
Xbox NUI Sensor (usb-0000:00:14.0-8):
	/dev/video0
	/dev/video1

$ v4l2-ctl --all
Driver Info:
	Driver name      : kinect2
	Card type        : Xbox NUI Sensor
	Bus info         : usb-0000:00:14.0-8
	Driver version   : 5.6.15
	Capabilities     : 0x85200001
		Video Capture
		Read/Write
		Streaming
		Extended Pix Format
		Device Capabilities
	Device Caps      : 0x05200001
		Video Capture
		Read/Write
		Streaming
		Extended Pix Format
Priority: 2
Video input : 0 (kinect2: ok)
Format Video Capture:
	Width/Height      : 1920/1080
	Pixel Format      : 'JPEG' (JFIF JPEG)
	Field             : None
	Bytes per Line    : 1920
	Size Image        : 2073600
	Colorspace        : JPEG
	Transfer Function : Default (maps to sRGB)
	YCbCr/HSV Encoding: Default (maps to ITU-R 601)
	Quantization      : Default (maps to Full Range)
	Flags             : 
Streaming Parameters Video Capture:
	Frames per second: invalid (0/0)
	Read buffers     : 2

[grandchild]

I can look into this tomorrow, but maybe copy the info here into a new issue, which mentions usb_submit_urb() -- so that others can find it, and if someone solves it be properly closed. This PR here solves what it was meant to solve. Thanks!

[grandchild]

The command I use to show Kinect2 output is:

mpv av://v4l2:/dev/video0 --untimed --profile=low-latency

[thamma]

The command I use to show Kinect2 output is:

mpv av://v4l2:/dev/video0 --untimed --profile=low-latency

This actually shows the footage. Thanks for your effort and your great contribution in the first place!

[grandchild]

In order to use the Kinect2 (which uses the MotionJPG/mjpg codec) with other programs that mostly don't support mjpg, say, as a webcam, I convert with ffmpeg in the background. You do need a v4l2loopback device for this!

ffmpeg \
    -i /dev/video0 \
    # don't do vsync, for less delay
    -vsync drop \
    # drop half the frames, and scale to 720p -- good enough for webcam use
    # also mirror horizontally for webcam use -- other cams do this intrinsically but we need to do it ourselves
    -filter:v fps=30,scale=1280:-1,hflip \
    # good general-purpose pixel format supported by many apps
    -pix_fmt yuyv422 \
    # convert the colorspace, so the colors look better (not blown out too much)
    -color_trc bt709 \
    -color_primaries bt709 \
    -color_range tv \
    # output device format
    -f v4l2 \
    # output device
    /dev/video2

(remove the comments)
/dev/video0 is the kinect rgb input.
/dev/video2 is the v4l2loopback device.
All options except -i ..., -f v4l2 and the output device are optional but recommended, if you want smaller delay. I still have quite a huge delay sometimes, but it can be good as well -- sadly really random when it works and when not.

I keep this running in the background, and can then use /dev/video2/ as webcam.