Movie.duration() always returns 0.0, framerate() and speed() do not seem to affect playback

I've just started to experiment with the Movie library and I've run into some basic questions.

Here's the testbed code:

import processing.video.*;
Movie myMovie;
int screenSizeX = 800;
int screenSizeY = 600;
float duration = 0;

void settings()
{
  size(screenSizeX, screenSizeY);
}
void setup() {

  myMovie = new Movie(this, "20180201103135_20180201103155_01_M.dav");
  myMovie.frameRate(25);
  myMovie.speed(0.01);
  duration = myMovie.duration();
  println("setup duration =" + duration);
  duration = myMovie.playbin.queryDuration().toSeconds();
  println("setup playbin.queryDuration() duration =" + duration);
  myMovie.loop();
}

void draw() {
  image(myMovie, 0, 0);
  println("Duration=" + myMovie.duration());
}

// Called every time a new frame is available to read
void movieEvent(Movie m) {
  m.read();
  duration = myMovie.duration();
  println("movieEvent duration =" + duration);
}

When I run it, duration always appear to return 0.0 regardless of when I test it -- including if I call playbin directly (mimicking the library code at line 270 here: https://github.com/processing/processing-video/blob/master/src/processing/video/Movie.java ).

The console output is:
setup duration =0.0
setup playbin.queryDuration() duration =0.0
movieEvent duration =0.0
Duration=0.0
Duration=0.0
movieEvent duration =0.0
Duration=0.0
:

What I was really trying to do (apart from experimenting with playback at various speeds) was figure out how to detect when a Movie has finished playing? I've seen some example code that did this:

if (myMovie.time() >= myMovie.duration()) // Test if the playhead is at the end
{
   // end of Movie
}

Of course that's destined to fail if .duration() always returns zero. So that raises the question, how do you tell when a movie has finished?? I supposed I could check when .time() stops changing, but that squawks a dreaded red text error on the console when the code runs "off the end" of the Movie.

Anyone got any ideas how you test for when a Movie has finished playing? I need to work my way through a directory with hundreds of different movie files and extract individual frames -- I've figured out what I thought would be the hard part only to screech to a halt on this "simple" problem. :(

Oh....and anyone got any ideas why myMovie.frameRate() and .speed() don't appear to do anything?

Thanks in advance Andy