StartVideoDynamic.cs

using Vuforia;
using UnityEngine;
using UnityEngine.Video;

public class StartVideoDynamic : MonoBehaviour, ITrackableEventHandler
{
    void Start()
    {
        GetComponent<VideoPlayer>().enabled = false;

        if (GetComponent<TrackableBehaviour>())
        {
            GetComponent<TrackableBehaviour>().RegisterTrackableEventHandler(this);
        }
    }

    public void OnTrackableStateChanged(TrackableBehaviour.Status previousStatus, TrackableBehaviour.Status newStatus)
    {
        if (newStatus == TrackableBehaviour.Status.DETECTED || newStatus == TrackableBehaviour.Status.TRACKED || newStatus == TrackableBehaviour.Status.EXTENDED_TRACKED)
        {
            GetComponent<VideoPlayer>().enabled = true;
            GetComponent<VideoPlayer>().Play();
        }
        else
        {
            //GetComponent<VideoPlayer>().enabled = false;
            GetComponent<VideoPlayer>().Pause();
        }
    }
}