Problem with ofVideoPlayer

//
I tried this sample code to mac,
to play video frame by frame,
and sometimes it works, and sometimes it is not working,
i get “pip” messagess writen in console, but, frames not changing, sometimes

-on space video plays
-but using 1, 2 frame by frame sometimes work sometimes now working.

i am some-how new learning oF,

inspired, used code from video tutorial at

//my .h file

#pragma once

#include “ofMain.h”

class ofApp : public ofBaseApp{

public:
	void setup();
	void update();
	void draw();

	void keyPressed(int key);
	void keyReleased(int key);
	void mouseMoved(int x, int y );
	void mouseDragged(int x, int y, int button);
	void mousePressed(int x, int y, int button);
	void mouseReleased(int x, int y, int button);
	void mouseEntered(int x, int y);
	void mouseExited(int x, int y);
	void windowResized(int w, int h);
	void dragEvent(ofDragInfo dragInfo);
	void gotMessage(ofMessage msg);
	

//my
ofVideoPlayer video_player_a;
//end my

};

//my .cpp file
#include “ofApp.h”

//--------------------------------------------------------------
void ofApp::setup(){
//my
video_player_a.loadMovie(“a.mp4”);
//video_player_a.load(“a.mp4”);
//end my
}

//--------------------------------------------------------------
void ofApp::update(){
video_player_a.update();
}

//--------------------------------------------------------------
void ofApp::draw(){
video_player_a.draw(200, 200, 300, 300);
}

//--------------------------------------------------------------
void ofApp::keyPressed(int key){
switch (key) {
case ’ ':
{
video_player_a.play();
//video_player_a.update();

        break;
    }
    case '1'://OF_KEY_LEFT:
    {
        
        video_player_a.previousFrame();
        //video_player_a.update();
        printf("pip A 5");

        break;
    }
    case'2':// OF_KEY_RIGHT:
    {
        video_player_a.nextFrame();
        //video_player_a.update();
        printf("pip B 5");
        break;
    }
}

}

//--------------------------------------------------------------
void ofApp::keyReleased(int key){
}

//--------------------------------------------------------------
void ofApp::mouseMoved(int x, int y ){

}

//--------------------------------------------------------------
void ofApp::mouseDragged(int x, int y, int button){

}

//--------------------------------------------------------------
void ofApp::mousePressed(int x, int y, int button){

}

//--------------------------------------------------------------
void ofApp::mouseReleased(int x, int y, int button){

}

//--------------------------------------------------------------
void ofApp::mouseEntered(int x, int y){

}

//--------------------------------------------------------------
void ofApp::mouseExited(int x, int y){

}

//--------------------------------------------------------------
void ofApp::windowResized(int w, int h){

}

//--------------------------------------------------------------
void ofApp::gotMessage(ofMessage msg){

}

//--------------------------------------------------------------
void ofApp::dragEvent(ofDragInfo dragInfo){

}