Camera


This chapter describes the common information and instructions for the camera on AIoT Yocto, such as setting camera hardware/software, launching the camera pipeline, and so on. The camera on different platforms may have some platform-specific instructions or test results. For example, you will have different camera settings on different platforms. Please refer to the platform-specific section to find more details.


Note

All cmd operations presented in this chapter are based on the AIoT Yocto v22.1, Genio 350-EVK. You might get different operation result depends on what platform you currently use.

v4l2-ctl

v4l2-ctl is a useful tool to dump the information of v4l2 devices. You can obtain the supported format, resolution, and controls. For more details, you can use command v4l2-ctl -h.

To list all available devices on the board:

v4l2-ctl --list-devices
...
mtk-camsys-3.0 (platform:15040000.seninf):
        /dev/media1

mtk-camsv-isp30 (platform:15050000.camsv):
        /dev/video3

mtk-camsv-isp30 (platform:15050800.camsv):
        /dev/video4

USB2.0 Camera: USB2.0 Camera (usb-11200000.xhci-2):
        /dev/video5
        /dev/video6
        /dev/media2
...

To obtain the format and the resolution supported by a video device:

v4l2-ctl -d /dev/video3 --all
...
Video input : 0 (1a051000.camsv video stream: ok)
Format Video Capture Multiplanar:
        Width/Height      : 2316/1746
        Pixel Format      : 'UYVY'
        Field             : None
        Number of planes  : 1
        Flags             :
        Colorspace        : sRGB
        Transfer Function : Default
        YCbCr/HSV Encoding: Default
        Quantization      : Default
        Plane 0           :
           Bytes per Line : 4632
           Size Image     : 8087472

GStreamer Pipeline Example

v4l2src

The camera implementation follows V4L2 standard. Therefore, you can operate the camera through GStreamer element, v4l2src. For more details about GStreamer, please refer to GStreamer.

In this section, there are two scenarios demonstrated:

  • Show camera images on the screen

  • Store camera images in the file

Show camera images on the screen

First, you need to find out which device node is the camera you want. The video device node which points to seninf will be the camera. In this example, the camera is /dev/video3.

ls -l /sys/class/video4linux/ | grep seninf
total 0
...
lrwxrwxrwx 1 root root 0 Sep 20  2020 video3 -> ../../devices/platform/soc/15040000.seninf/video4linux/video3
...

Then you can show the full-size camera image to the screen through waylandsink.

gst-launch-1.0 v4l2src device=/dev/video3 ! video/x-raw,width=2316,height=1746,format=UYVY ! videoconvert ! waylandsink sync=false

You may feel that the image is too big to be accommodated on the screen. In this case, you can use the GStreamer element, v4l2convert, which will use the hardware converter, MDP, to resize the image.

gst-launch-1.0 v4l2src device=/dev/video3 ! video/x-raw,width=2316,height=1746,format=UYVY ! v4l2convert output-io-mode=dmabuf-import ! video/x-raw,width=400,height=300 ! waylandsink sync=false

Store camera images in the file

To store camera images, you can use filesink as output. By the following command, the camera images will be saved in /home/root/out.yuv

gst-launch-1.0 v4l2src device=/dev/video3 num-buffers=1 ! video/x-raw,width=2316,height=1746,format=UYVY ! filesink location=/home/root/out.yuv

You can use filesrc to show the saved images.

gst-launch-1.0 filesrc location=/home/root/out.yuv blocksize=8087472 ! videoparse width=2316 height=1746 format=uyvy framerate=1 ! videoconvert ! waylandsink

libcameasrc

On AIoT Yocto, you can also use the GStreamer element, libcamerasrc, to demonstrate the camera pipeline.

First, you need to determine which camera you want to use. The libcamera utility cam can help.

cam -l
Available cameras:
1: Internal front camera (/base/soc/i2c@11009000/camera@3d)
2: Internal front camera (/base/soc/i2c@1100f000/camera@3d)
3: 'USB2.0 Camera: USB2.0 Camera' (/base/soc/usb@11201000/xhci@11200000-2:1.0-1e4e:0102)

Second, select the camera you want and record its name. For example, the name of the first camera above is /base/soc/i2c@11009000/camera@3d.

Third, use the GStreamer command with a specified camera name to show the camera images on the screen.

gst-launch-1.0 libcamerasrc camera-name="/base/soc/i2c@11009000/camera@3d" ! video/x-raw,format=RGB ! v4l2convert output-io-mode=dmabuf-import ! video/x-raw,width=400,height=300 ! waylandsink sync=false

For more details about the GStreamer elements, libcamerasrc, you can use gst-inspect-1.0 command to list details, templates, and properties.

gst-inspect-1.0 libcamerasrc
...
Plugin Details:
  Name                     libcamera
  Description              libcamera capture plugin
  Filename                 /usr/lib64/gstreamer-1.0/libgstlibcamera.so
...
Pad Templates:
  SRC template: 'src'
    Availability: Always
    Capabilities:
      video/x-raw
      image/jpeg
    Type: GstLibcameraPad
    Pad Properties:
      stream-role         : The selected stream role
                            flags: readable, writable, changeable only in NULL or READY state
                            Enum "GstLibcameraStreamRole" Default: 2, "video-recording"
                               (1): still-capture    - libcamera::StillCapture
                               (2): video-recording  - libcamera::VideoRecording
                               (3): view-finder      - libcamera::Viewfinder
...
Element Properties:
  camera-name         : Select by name which camera to use.
                        flags: readable, writable, changeable only in NULL or READY state
                        String. Default: null
  name                : The name of the object
                        flags: readable, writable
                        String. Default: "libcamerasrc0"
  parent              : The parent of the object
                        flags: readable, writable
                        Object of type "GstObject"
...

USB Camera

AIoT Yocto supports USB Video Class (UVC). You can use a USB webcam as a v4l2 video device and operate through GStreamer. To find out the USB camera, you can use the following two methods:

  • For v4l2 device node

ls -l /sys/class/video4linux
...
lrwxrwxrwx 1 root root 0 Oct  8 01:29 video5 -> ../../devices/platform/soc/11201000.usb/11200000.xhci/usb1/1-1/1-1.3/1-1.3:1.0/video4linux/video5
...
  • For libcamera name

cam -l
Available cameras:
1: Internal front camera (/base/soc/i2c@11009000/camera@3d)
2: Internal front camera (/base/soc/i2c@1100f000/camera@3d)
3: 'USB2.0 Camera: USB2.0 Camera' (/base/soc/usb@11201000/xhci@11200000-1.3:1.0-1e4e:0102)

In this example, the video device node of the USB camera is /dev/video5, and the camera name is /base/soc/usb@11201000/xhci@11200000-1.3:1.0-1e4e:0102. Next, you can operate your camera through GStreamer, given either the device node or the libcamera name.

  • To use v4l2src

gst-launch-1.0 v4l2src device=/dev/video5 io-mode=mmap ! videoconvert ! waylandsink sync=false

Note

UVC driver uses CPU to compose the frame buffer from several USB packets, so the memory mode should be mmap. Otherwise, if the memory mode is dmabuf, the consumer of UVC won’t flush the CPU cache leading to the dirty image issue.

  • To use libcamerasrc

gst-launch-1.0 libcamerasrc camera-name="/base/soc/usb@11201000/xhci@11200000-1.3:1.0-1e4e:0102" ! videoconvert ! waylandsink sync=false