android（linux）控制uvc相机实现ptz

Question

I want to control a ptz camera from android,actually i do that in jni and use linux api,the camera is connected to android-tvbox's usb interface directly, ,below is the code:

    struct v4l2_ext_control xctrls[1];
    struct v4l2_ext_controls ctrls;

    memset(xctrls, 0, sizeof xctrls);
    memset(&ctrls, 0, sizeof ctrls);
    xctrls[0].id = V4L2_CID_PAN_ABSOLUTE;
    xctrls[0].value = 20;
    ctrls.ctrl_class = V4L2_CTRL_CLASS_CAMERA;
    ctrls.count = 1;
    ctrls.controls = xctrls;
    //xioctl(fd, VIDIOC_S_EXT_CTRLS, &ctrls);
    int result = ioctl(fd, VIDIOC_S_CTRL, &ctrls);
    //LOGE("Cannot identify:%d , %d, %s", result, errno, strerror (errno));
    LOGE("Cannot open '%d': %d, %s", result, errno, strerror (errno));

and it return invalid argument , can anyone tell me which argument is wrong?Or my code is incorrect...

Answer 1

I have solved this problem. Actually, you need to design your Android source code in UVC (USB Video Class) module, and UVC is located in the kernel of the whole android source code.

What's more, you have to cooperate with the camera's vendor, because they have deep insights into the firmware of PTZ cameras, and Android's UVC version should apply to camera firmware, data length and control type (absolute or relative).

Furthermore, Android kernel's version is generally 3.10. When you control camera with absolute control, it may move in one direction but not another one, because the Android UVC control parameters of absolute is unsigned: you should change it to signed parameters.

When you control in relative, it's a little more complicated, for you should add relative control in Android source code because Android kernel in 3.10 does not support it. You can get the Linux kernel patch to add relative movements.