Android4OpenCV: setting resolution at startup

edit

I'm using Android4OpenCV to do some live image processing, and I'd like to use the smallest resolution the camera can offer. The default resolution is the largest the camera can offer.

I'm looking at the 3rd example, which allows the user to change resolutions via a menu. I'd like to modify that example to change the resolution at startup instead of requiring the user go through the menu. To do that, I simply add two lines to the otherwise empty onCameraViewStarted() function:

public void onCameraViewStarted(int width, int height) {
    android.hardware.Camera.Size res = mOpenCvCameraView.getResolutionList().get(mOpenCvCameraView.getResolutionList().size()-1);
    mOpenCvCameraView.setResolution(res);
}

And the thing is, this works perfectly fine on my Galaxy Nexus, running Android 4.2.2. The app starts up, and the resolution is set correctly.

However, when I run the exact same app on a Nexus 7 tablet, running Android 5.1, the app hangs on the call to setResolution(). Actually it works okay one time, but then hangs the second time you try to run it- even if you completely exit the app, remove it from the running apps, or restart the device. Other users are reporting the same error as well, so it's not just the Nexus 7 device- in fact, my Galaxy Nexus seems to be the only device where this works.

Specifically, the application goes into the setResolution() function, which then calls org.opencv.android.JavaCameraView.disconnectCamera(), which looks like this:

(Note: this code is internal to the OpenCV4Android library, this is not my code)

protected void disconnectCamera() {
    /* 1. We need to stop thread which updating the frames
     * 2. Stop camera and release it
     */
    Log.d(TAG, "Disconnecting from camera");
    try {
        mStopThread = true;
        Log.d(TAG, "Notify thread");
        synchronized (this) {
            this.notify();
        }
        Log.d(TAG, "Wating for thread");
        if (mThread != null)
            mThread.join();
    } catch (InterruptedException e) {
        e.printStackTrace();
    } finally {
        mThread =  null;
    }

    /* Now release camera */
    releaseCamera();
}

Looking at the logs, I can see that the thread gets stuck on the synchronized(this) line. The only other thing that synchronizes on that Object is the inner JavaCameraView.CameraWorker class, which is the mThread variable in the above code, started by the JavaCameraView class:

(Note: this code is internal to the OpenCV4Android library, this is not my code)

private class CameraWorker implements Runnable {

    public void run() {
        do {
            synchronized (JavaCameraView.this) {
                try {
                    JavaCameraView.this.wait();
                } catch (InterruptedException e) {
                    // TODO Auto-generated catch block
                    e.printStackTrace();
                }
            }

            if (!mStopThread) {
                if (!mFrameChain[mChainIdx].empty())
                    deliverAndDrawFrame(mCameraFrame[mChainIdx]);
                mChainIdx = 1 - mChainIdx;
            }
        } while (!mStopThread);
        Log.d(TAG, "Finish processing thread");
    }
}

I've tried futzing with that code, changing the notify() to notifyAll(), and maintaining a List of CameraWorker threads and joining each one. But no matter what, the app still hangs at the disconnectCamera() call.

My questions are:

• How can I modify the third OpenCV4Android example so that its resolution is set at startup?

• What is causing the app to hang?

• Why does this work on some devices but not others?

I've also posted ... (more)