var mov: MovieTexture;
var gui: GUIText;

function Start() {
    gui.text = mov.duration.ToString();
}

using UnityEngine;
using System.Collections;

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

import UnityEngine
import System.Collections

class example(MonoBehaviour):

    public mov as MovieTexture

    public gui as GUIText

    def Start():
        gui.text = mov.duration.ToString()