How do I sync up the video and audio from my movie?

Hi guys, I'm trying to play a .avi video in unity which I have put on a plane and it's working fine but the audio is a few seconds out of sync with the video which makes it unbearable to watch. Does anyone know how to sync up video and audio so that it plays at the same time?

 using UnityEngine;
 using System.Collections;
 [RequireComponent (typeof(AudioSource))]
 
 public class PlayVideo : MonoBehaviour {
         
     // Use this for initialization
     void OnMouseUp(){    
           MovieTexture PL1 = renderer.material.mainTexture as MovieTexture;
         audio.clip = PL1.audioClip;
         
         audio.Play();
         PL1.Play ();
      }
 
     
     // Update is called once per frame
     void Update () {
     }
 }