How to open usb camera in android using android.hardware.camera.external

For me works the next config for USB Cameras with official API:

Camera (old API)

On some china devices, Camera.CameraInfo.CAMERA_FACING_FRONT works, but some times your should force to camIdx to 0.

public static Camera getCameraInstance() {
    Camera c = null;
    try {
        Camera.CameraInfo cameraInfo = new Camera.CameraInfo();
        int cameraCount = Camera.getNumberOfCameras();
        for (int camIdx = 0; camIdx < cameraCount; camIdx++) {
            Camera.getCameraInfo(camIdx, cameraInfo);
            Log.i(TAG, "[Camera] try to open camera camIdx:" + camIdx);
            if (cameraInfo.facing == Camera.CameraInfo.CAMERA_FACING_FRONT) {
                try {
                    c = Camera.open(camIdx);
                    mCameraIdx = camIdx;
                    Log.i(TAG, "[Camera] camIdx:" + camIdx);
                } catch (RuntimeException e) {
                    Log.e(TAG, "[Camera] failed to open: " + e.getLocalizedMessage());
                }
            }
        }

        if (c == null) {
            Log.i(TAG, "[Camera] forcing open camera with camIdx 0");
            c = Camera.open(0); // force because FACING_FRONT not found
            mCameraIdx = 0;
        }
    } catch (Exception e) {
        Logger.e("TAG", "[Camera] Open camera failed: " + e);
    }
    return c;
}

Camera2 (new API)

Similar for Camera2 API:

public String getCamera(CameraManager manager) {

    String cameraIndex = "0";
    try {
        for (String cameraId : manager.getCameraIdList()) {
            CameraCharacteristics characteristics = manager.getCameraCharacteristics(cameraId);
            Logger.d(TAG, "cameraId " + cameraId);
            int cOrientation = characteristics.get(CameraCharacteristics.LENS_FACING);
            if (cOrientation != CAMERACHOICE) {
                cameraIndex = cameraId;
            }
        }
    } catch (CameraAccessException e) {
        e.printStackTrace();
    }
    return cameraIndex;
}

But in my experience some Android ROM implementations are really bad (sometimes custom hardware or china hardware) then it not works. In some situations you should be use libuvc driver fore some USB Cameras: https://github.com/saki4510t/UVCCamera

There's currently (as of Android O) no common USB camera support on Android devices via the standard camera API.

Some Android manufacturers do have their own support for USB cameras, but it's hard to know what devices do and what don't.