Use mousePressed(), the function, instead. Because with the variable, if you click over several frames (60 per second! so it is likely...), you end in an unknown state...
BTW, i = 0; i++; is the same that i = 1;...

Many thanks, could you please give me a similar example which easy for me to understand. It's the first time I am tring using processing...

1. int i=0;
   import processing.video.*;
   Movie myMovie;
   
   void setup() {
   
   
     size(300, 200);
     background(0);
     myMovie = new Movie(this, "1.mp4");
     myMovie.loop();
     myMovie.pause();
   }
   
   void movieEvent(Movie m) {
     m.read();
   }
   
   void draw() {
   
   
     background(255);
     image(myMovie, 0, 0, 300, 200);
   }
   
   void mousePressed()
   
   {
     if (i==0) {
       i=1;
       myMovie.play();
     }
     else {
       i=0;
       myMovie.pause();
     }
   }