[Interest] USB Webcams in Android?

[Jason H]

It also looks like /dev/video0 is provided specifically for USB webcam support. It is opened, then ioctls use VIDIOC_QBUF to get a frame from the camera.
I don't know how this will work with Qt. It looks like I need to build Qt with both android and v4l support? It looks like v4l support in Qt is limited to radio?


> Sent: Tuesday, April 10, 2018 at 11:09 AM
> From: "Jason H" <jhihn at gmx.com>
> To: "interestqt-project.org" <interest at qt-project.org>
> Subject: [Interest] USB Webcams in Android?
>
> I'm wondering what it would take to get USB webcams working in Qt on Android. It seems that if the kernel already supports it, it will be listed as as /dev/v* device.
> 
> I'm also wondering what Qt needs to use the device? I plugged it in and it did not appear in QtMultimedia.availableCameras:  
> [
>   {"deviceId":"back","displayName":"Rear-facing camera","position":1,"orientation":270},
>   {"deviceId":"front","displayName":"Front-facing camera","position":2,"orientation":90}
> ]
> 
> Additionally, it seems that many camera apps don't support USB cameras and USB camera apps don't support the built-in cameras. 
> The only hint at what is going on is this line in logcat: 04-10 10:59:05.360 14692 14886 I USBMonitor: name=/dev/bus/usb/001/002,desc=86,busnum=1,devnum=2,rawDesc=[B at 6930dda
> 
> 
> Many thanks!
> 
> Here's what my Android kernel is saying:
> [ 2026.007529] PMI: smblib_vbus_regulator_enable: Enabling internal vbus regulator
> [ 2026.014142] msm-dwc3 a800000.ssusb: DWC3 exited from low power mode
> [ 2026.019444] xhci-hcd xhci-hcd.0.auto: xHCI Host Controller
> [ 2026.019548] xhci-hcd xhci-hcd.0.auto: new USB bus registered, assigned bus number 1
> [ 2026.026489] xhci-hcd xhci-hcd.0.auto: hcc params 0x0230fe65 hci version 0x110 quirks 0x00010010
> [ 2026.026595] xhci-hcd xhci-hcd.0.auto: irq 732, io mem 0x0a800000
> [ 2026.027069] usb usb1: New USB device found, idVendor=1d6b, idProduct=0002
> [ 2026.027101] usb usb1: New USB device strings: Mfr=3, Product=2, SerialNumber=1
> [ 2026.027130] usb usb1: Product: xHCI Host Controller
> [ 2026.027156] usb usb1: Manufacturer: Linux 4.4.88-gda039c93611c xhci-hcd
> [ 2026.027182] usb usb1: SerialNumber: xhci-hcd.0.auto
> [ 2026.035180] hub 1-0:1.0: USB hub found
> [ 2026.036400] hub 1-0:1.0: 1 port detected
> [ 2026.037148] xhci-hcd xhci-hcd.0.auto: xHCI Host Controller
> [ 2026.037195] xhci-hcd xhci-hcd.0.auto: new USB bus registered, assigned bus number 2
> [ 2026.037435] usb usb2: We don't know the algorithms for LPM for this host, disabling LPM.
> [ 2026.037767] usb usb2: New USB device found, idVendor=1d6b, idProduct=0003
> [ 2026.037798] usb usb2: New USB device strings: Mfr=3, Product=2, SerialNumber=1
> [ 2026.037825] usb usb2: Product: xHCI Host Controller
> [ 2026.037851] usb usb2: Manufacturer: Linux 4.4.88-gda039c93611c xhci-hcd
> [ 2026.037877] usb usb2: SerialNumber: xhci-hcd.0.auto
> [ 2026.043081] hub 2-0:1.0: USB hub found
> [ 2026.043804] hub 2-0:1.0: 1 port detected
> [ 2026.342230] usb 1-1: new high-speed USB device number 2 using xhci-hcd
> [ 2026.485458] usb 1-1: New USB device found, idVendor=a16f, idProduct=0304
> [ 2026.485503] usb 1-1: New USB device strings: Mfr=2, Product=3, SerialNumber=0
> [ 2026.485526] usb 1-1: Product: USB2.0 UVC PC Camera
> [ 2026.485548] usb 1-1: Manufacturer: GenesysLogic Technology Co., Ltd.
> [ 2026.545861] PMI: smblib_set_prop_use_external_vbus_output: VBUS output source: internal -> extern
> 
> walleye:/dev # ls -al v*
> crw-rw---- 1 system camera 81, 128 1970-06-12 03:04 v4l-subdev0
> crw-rw---- 1 system camera 81, 129 1970-06-12 03:04 v4l-subdev1
> crw-rw---- 1 system camera 81, 138 1970-06-12 03:04 v4l-subdev10
> crw-rw---- 1 system camera 81, 139 1970-06-12 03:04 v4l-subdev11
> crw-rw---- 1 system camera 81, 140 1970-06-12 03:04 v4l-subdev12
> crw-rw---- 1 system camera 81, 141 1970-06-12 03:04 v4l-subdev13
> crw-rw---- 1 system camera 81, 142 1970-06-12 03:04 v4l-subdev14
> crw-rw---- 1 system camera 81, 143 1970-06-12 03:04 v4l-subdev15
> crw-rw---- 1 system camera 81, 144 1970-06-12 03:04 v4l-subdev16
> crw-rw---- 1 system camera 81, 145 1970-06-12 03:04 v4l-subdev17
> crw-rw---- 1 system camera 81, 146 1970-06-12 03:04 v4l-subdev18
> crw-rw---- 1 system camera 81, 147 2018-04-10 09:47 v4l-subdev19
> crw-rw---- 1 system camera 81, 130 1970-06-12 03:04 v4l-subdev2
> crw-rw---- 1 system camera 81, 148 2018-04-10 09:47 v4l-subdev20
> crw-rw---- 1 system camera 81, 131 1970-06-12 03:04 v4l-subdev3
> crw-rw---- 1 system camera 81, 132 1970-06-12 03:04 v4l-subdev4
> crw-rw---- 1 system camera 81, 133 1970-06-12 03:04 v4l-subdev5
> crw-rw---- 1 system camera 81, 134 1970-06-12 03:04 v4l-subdev6
> crw-rw---- 1 system camera 81, 135 1970-06-12 03:04 v4l-subdev7
> crw-rw---- 1 system camera 81, 136 1970-06-12 03:04 v4l-subdev8
> crw-rw---- 1 system camera 81, 137 1970-06-12 03:04 v4l-subdev9
> crw------- 1 root   root   10,  95 1970-06-12 03:04 vga_arbiter
> crw-rw---- 1 system camera 81,   0 1970-06-12 03:04 video0
> crw-rw---- 1 system camera 81,   1 1970-06-12 03:04 video1
> crw-rw---- 1 system camera 81,   2 1970-06-12 03:04 video2
> crw-rw---- 1 system camera 81,   3 1970-06-12 03:04 video3
> crw-rw---- 1 system camera 81,  32 1970-06-12 03:04 video32
> crw-rw---- 1 system camera 81,  33 1970-06-12 03:04 video33
> crw-rw---- 1 system camera 81,   4 2018-04-10 09:47 video4
> crw-rw---- 1 system camera 81,   5 2018-04-10 09:47 video5
> crw-rw-rw- 1 root   root   10,  47 1970-06-12 03:04 vndbinder
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