连接的USB设备的Android设备节点名称

Question

I am currently writing an application for an Android nexus 5 phone. The application uses gstreamer that runs natively to access a usb webcam that has been plugged into the device. In order to access the webcam I need the device node location of the webcam. Generally it is /dev/video3 but sometimes it changes values, ie /dev/video4

Currently I have to set the device node location manually for this to work. I wish to render the process automatic. Especially given the case where a user could disconnect and reconnect the webcam.

So far, I can determine the vendorID, productID from Java, I then pass this info to my C code using JNI.

I use the following to detect the USB device info :

if (UsbManager.ACTION_USB_DEVICE_ATTACHED.equals(action)) 
        {
            deviceFound = (UsbDevice)intent.getParcelableExtra(UsbManager.EXTRA_DEVICE);

            Log.i("TAG", "USB DEVICE ATTACHED");

            deviceFound.getDeviceName();
            deviceFound.getVendorId();
            deviceFound.getProductId();

        }

getDeviceName returns a string that contains "/dev/bus/usb/001/002". If I try using this to access my webcam using gstreamer I get the following error "Error getting capabilities for device '/dev/bus/usb/001/002': It isn't a v4l2 driver"

I'm assuming that /dev/bus/usb/002/001 isn't quite the same as /dev/video3 in this case. A few questions :

1) Can I obtain the correct device node ie /dev/video3 using /dev/bus/usb/001/002 ?

2) Is there a way of directly obtaining the device node (/dev/video*) given the USB device's vendor & product identifiers programmatically ?

Thanks.

Answer 1

Check the modification time on all candidates in /dev/video* . You are looking for the one close to the time you received USB_DEVICE_ATTACHED action.

Answer 2

Android have USB accessory APIs (android.hardware.usb) in which you can get when any USB device attach or detach from android device and add

to manifest and this intent filter to

<intent-filter>
       <action android:name="android.hardware.usb.action.USB_ACCESSORY_ATTACHED" /> 
</intent-filter>

to activity in manifest

UsbManager mUsbManager = (UsbManager) getSystemService(Context.USB_SERVICE);

from this you can get system service for USB

UsbAccessory[] accessories = mUsbManager.getAccessoryList();

You will get a list of currently attached USB accessories. it reports its manufacturer and model names, the version of the accessory, and a user visible description of the accessory to the device.

HashMap<String,UsbDevice> result= mUsbManager.getDeviceList()

Returns a HashMap containing all USB devices currently attached. USB device name is the key for the returned HashMap. And UsbDevice contains manufacturer and model names, the version etc.

For more detailed description Read Android Developer