Saving frames when frameRate%15 is not working

elunicotomas

Hello there,

I have this code that saves a frame from the webcam everytime frameRate%15 ==0, and I only want 30 frames total.

Whit a frameRate of 60fps I should have 4 frames per second, but is not the case (it's not saving any frame) and i don't know why, any ideas?

I'm using Processing 2.2.1

import processing.video.*;
Capture cam;
int frames = 0;

void setup() {
  size(640, 480);
  String[] cameras = Capture.list();

  if (cameras.length == 0) {
    println("There are no cameras available for capture.");
    exit();
  } else {
    println("Available cameras:");
    for (int i = 0; i < cameras.length; i++) {
      println(cameras[i]);
    }
    cam = new Capture(this, cameras[1]);
    cam.start();
  }
  background(0);
}

void draw() {
  if (mousePressed) {
    if (cam.available() == true) {
      cam.read();
      image(cam, 0, 0);
      if (frameCount % 15 == 0) {
        saveFrame("frames/" + frames + ".png"); //voy guardando frames
        frames++;
      }
      if (frames > 29) {
        frames = 0;
      }
    }
  } else {
    background(0);
  }

  print("frame count: ");
  print(frameCount);
  print("  |  framerate: ");
  println(frameRate);
}

billhsu

The problem is you only save the frame when cam.available() == true. You don't always get a new image from the camera every time you call draw(). So frameCount % 15 == 0 will be false, more often than once every 15 frames. (Frames 0, 15, 30 etc may not be frames where a new image is available.)

If you want to save one out of every 15 available frames, you can create a counter that counts just the available frames, and use the % operation on that counter.

Or if you want to save (say) 4 frames per second, you can check the timestamp instead of the frameCount. Note that saving a frame is slow and will quite likely slowly down your code for that call to draw().

Chrisir

yeah, do this

if (frameCount % 15 == 0) {
        saveFrame("frames/" + frames + ".png"); //voy guardando frames
        frames++;
      }

outside the ifs

elunicotomas

Now I get it, thanks billhsu and Chrisir!

Just one question, when you say "Note that saving a frame is slow and will quite likely slowly down your code for that call to draw()." is there any way to save frames outside the draw?

Chrisir

hm...

you could store the images in an ArrayList and when the movie is over write them to the hard drive from there.

elunicotomas

thanks again! I'll try that later.

PhiLho

Note that the way you use saveFrame(), it could be replaced by frame(). saveFrame() is best used with a pattern numbering the frames automatically.

elunicotomas

@PhiLho Do you mean using the line frame() instead of saveFrame() ?

Like this?

frame("frames/" + frames + ".png");

PhiLho

Ouch, I meant to use save() instead of saveFrame(). frame() is a different thing!

elunicotomas

@PhiLho I got it ! thakns