proper video streaming with rxjava - opencv

Question

To handle a video stream from a webcam (delivered by opencv) i am considering to use RxJava.
I am hoping to achieve the following:
being able to control the frames per second to be delivered
to be able to handle different inputs - e.g. a life webcam, a video or even a still picture
being able to switch to a picture-by-picture handling under the control of a gui
I have been experimenting a bit with RxJava but i am confused about the debounce, throttleFirst and async operators
Examples like https://stackoverflow.com/a/48723331/1497139 show some code but I am missing more detailed explanation.
Where could I find a decent example for video processing or something similar along the needs mentioned above?
The code below does some non async logic at this time - please let me know if i could build on it:
ImageFetcher
import org.opencv.core.Mat;
import org.opencv.videoio.VideoCapture;
import rx.Observable;
import rx.functions.Action1;
import rx.functions.Func0;
import rx.functions.Func1;
/**
* fetcher for Images
*
*/
public class ImageFetcher {
// OpenCV video capture
private VideoCapture capture = new VideoCapture();
private String source;
protected int frameIndex;
public int getFrameIndex() {
return frameIndex;
}
/**
* fetch from the given source
*
* #param source
* - the source to fetch from
*/
public ImageFetcher(String source) {
this.source = source;
}
/**
* try opening my source
*
* #return true if successful
*/
public boolean open() {
boolean ret = this.capture.open(source);
frameIndex=0;
return ret;
}
/**
* fetch an image Matrix
*
* #return - the image fetched
*/
public Mat fetch() {
if (!this.capture.isOpened()) {
boolean ret = this.open();
if (!ret) {
String msg = String.format(
"Trying to fetch image from unopened VideoCapture and open %s failed",
source);
throw new IllegalStateException(msg);
}
}
final Mat frame = new Mat();
this.capture.read(frame);
frameIndex++;
return !frame.empty() ? frame : null;
}
#Override
protected void finalize() throws Throwable {
super.finalize();
}
/**
* convert me to an observable
* #return a Mat emitting Observable
*/
public Observable<Mat> toObservable() {
// Resource creation.
Func0<VideoCapture> resourceFactory = () -> {
VideoCapture capture = new VideoCapture();
capture.open(source);
return capture;
};
// Convert to observable.
Func1<VideoCapture, Observable<Mat>> observableFactory = capture -> Observable
.<Mat> create(subscriber -> {
boolean hasNext = true;
while (hasNext) {
final Mat frame = this.fetch();
hasNext = frame!=null && frame.rows()>0 && frame.cols()>0;
if (hasNext) {
String msg = String.format("->%6d:%4dx%d", frameIndex, frame.cols(), frame.rows());
System.out.println(msg);
subscriber.onNext(frame);
}
}
subscriber.onCompleted();
});
// Disposal function.
Action1<VideoCapture> dispose = VideoCapture::release;
return Observable.using(resourceFactory, observableFactory, dispose);
}
}
ImageSubscriber
import org.opencv.core.Mat;
import rx.Subscriber;
public class ImageSubscriber extends Subscriber<Mat> {
public Throwable error;
public int cols = 0;
public int rows=0;
public int frameIndex=0;
public boolean completed = false;
public boolean debug = false;
#Override
public void onCompleted() {
completed = true;
}
#Override
public void onError(Throwable e) {
error = e;
}
#Override
public void onNext(Mat mat) {
cols = mat.cols();
rows = mat.rows();
frameIndex++;
if (cols==0 || rows==0)
System.err.println("invalid frame "+frameIndex);
if (debug) {
String msg = String.format("%6d:%4dx%d", frameIndex, cols, rows);
System.out.println(msg);
}
}
};