Video files are not playing, only the sound..

I have this problem, i want the video to play in my game, but it doesn't work.. I use mp4 files. The problem is the sound plays but the video doesn't, it's just black screen.. And if i play the video in 'play mode' or then i 'build the game', the whole program is not responding.. Even in the preview, then i play longer videos.. (in 'project tab').. The only thing i can hear is audio.. I don't understand.. can anyone give me a hand, because i'm out of options write now.. i tried everything..

Used script: using UnityEngine; using System.Collections;

[RequireComponent (typeof(AudioSource)) ]

public class Video : MonoBehaviour {

 public MovieTexture movie;


 // Use this for initialization
 void Start () 
 {
     renderer.material.mainTexture = movie as MovieTexture;
     audio.clip = movie.audioClip;
     movie.Play();
     audio.Play();
 }

}