diff --git a/app/src/main/java/com/jiangdg/usbcamera/view/USBCameraActivity.java b/app/src/main/java/com/jiangdg/usbcamera/view/USBCameraActivity.java
index 5e527ec..9046731 100644
--- a/app/src/main/java/com/jiangdg/usbcamera/view/USBCameraActivity.java
+++ b/app/src/main/java/com/jiangdg/usbcamera/view/USBCameraActivity.java
@@ -72,10 +72,6 @@ public class USBCameraActivity extends AppCompatActivity implements CameraDialog
 
         @Override
         public void onAttachDev(UsbDevice device) {
-            if (mCameraHelper == null || mCameraHelper.getUsbDeviceCount() == 0) {
-                showShortMsg("check no usb camera");
-                return;
-            }
             // request open permission
             if (!isRequest) {
                 isRequest = true;
@@ -141,7 +137,7 @@ public class USBCameraActivity extends AppCompatActivity implements CameraDialog
         mUVCCameraView = (CameraViewInterface) mTextureView;
         mUVCCameraView.setCallback(this);
         mCameraHelper = UVCCameraHelper.getInstance();
-        mCameraHelper.setDefaultFrameFormat(UVCCameraHelper.FRAME_FORMAT_YUYV);
+        mCameraHelper.setDefaultFrameFormat(UVCCameraHelper.FRAME_FORMAT_MJPEG);
         mCameraHelper.initUSBMonitor(this, mUVCCameraView, listener);
 
 
diff --git a/libusbcamera/src/main/java/com/jiangdg/usbcamera/UVCCameraHelper.java b/libusbcamera/src/main/java/com/jiangdg/usbcamera/UVCCameraHelper.java
index 20e20b7..7dd26f8 100644
--- a/libusbcamera/src/main/java/com/jiangdg/usbcamera/UVCCameraHelper.java
+++ b/libusbcamera/src/main/java/com/jiangdg/usbcamera/UVCCameraHelper.java
@@ -238,6 +238,7 @@ public class UVCCameraHelper {
         List<DeviceFilter> deviceFilters = DeviceFilter
                 .getDeviceFilters(mActivity.getApplicationContext(), R.xml.device_filter);
         if (mUSBMonitor == null || deviceFilters == null)
+//            throw new NullPointerException("mUSBMonitor ="+mUSBMonitor+"deviceFilters=;"+deviceFilters);
             return null;
         // matching all of filter devices
         return mUSBMonitor.getDeviceList(deviceFilters);
diff --git a/libusbcamera/src/main/java/com/serenegiant/usb/USBMonitor.java b/libusbcamera/src/main/java/com/serenegiant/usb/USBMonitor.java
index c51e567..0fe041d 100644
--- a/libusbcamera/src/main/java/com/serenegiant/usb/USBMonitor.java
+++ b/libusbcamera/src/main/java/com/serenegiant/usb/USBMonitor.java
@@ -181,6 +181,7 @@ public final class USBMonitor {
 				mPermissionIntent = PendingIntent.getBroadcast(context, 0, new Intent(ACTION_USB_PERMISSION), 0);
 				final IntentFilter filter = new IntentFilter(ACTION_USB_PERMISSION);
 				// ACTION_USB_DEVICE_ATTACHED never comes on some devices so it should not be added here
+				filter.addAction(ACTION_USB_DEVICE_ATTACHED);
 				filter.addAction(UsbManager.ACTION_USB_DEVICE_DETACHED);
 				context.registerReceiver(mUsbReceiver, filter);
 			}
@@ -311,7 +312,15 @@ public final class USBMonitor {
 		final HashMap<String, UsbDevice> deviceList = mUsbManager.getDeviceList();
 		// store those devices info before matching filter xml file
 		String fileName = Environment.getExternalStorageDirectory()+ "/USBCamera/failed_devices.txt";
+
 		File logFile = new File(fileName);
+		if(! logFile.exists()) {
+			try {
+				logFile.createNewFile();
+			} catch (IOException e) {
+				e.printStackTrace();
+			}
+		}
 		FileWriter fw = null;
 		PrintWriter pw = null;
 		final List<UsbDevice> result = new ArrayList<UsbDevice>();