MovieTexture.duration

Description

The time, in seconds, that the movie takes to play back completely.

Note that duration is only available once the movie has started. Until then duration will return -1. If you need to know the duration of a movie before it is played, consider extracting this information offline and creating a text asset. You can then look up the duration given the movie name.

using UnityEngine;
using System.Collections;

public class ExampleClass : MonoBehaviour {
    public MovieTexture mov;
    public GUIText gui;
    void Start() {
        gui.text = mov.duration.ToString();
    }
}