using the Rectangle tool. 1. Select the Video layer, and click the Insert Layer icon. Name the new layer Mask. 2. Select the Rectangle tool, with no stroke and a solid fill in any color. 3. Draw a rectangle on the Stage, and select it with the Selection tool. 4. In the Property inspector, set the width and height of the rectangle to 300. Set the X and Y values to 0. [View full size image] 5. Right-click (Windows) or Control-click (Mac OS) the Mask layer, and select Mask. 6. Choose Control > Test Movie to see the effect. The video should disappear when it slides off the Stage. You've made an ordinary project much more engaging with sound and video files imported from other sources.   Review Review Questions 1 How can you edit the length of a sound clip 2 What is a skin for a video 3 What are the limitations for embedded video clips 4 What is a green screen and how is it used Review Answers 1 To edit the length of a sound clip, select the frame that contains it, and click Edit in the Property inspector. Then, move the time slider in the Edit Envelope dialog box. 2 The skin is the combination and appearance of video controls, such as Play, Fast Forward, and Pause buttons. You can choose from a wide array of combinations, with the buttons in different positions, and you can customize the skin. If you don't want viewers to have control over the video, apply no skin. 3 When you embed a video clip, it becomes part of the Flash document and is included in the Timeline. Because embedded video clips significantly increase the size of the document and produce audio synchronization issues, it's best to embed video only if it is less than 10 seconds in length and contains no audio track. 4 A green screen is a solid color background shot behind a video subject. The solid background is then removed from the footage in an application such as After Effects, so that the subject can be placed in front of a different background. 10. Loading and Optimizing Flash Content A preloader keeps your viewers engaged while the primary movie file loads. Be creative in designing the preloader, and then use ActionScript to put it to work. Lesson Overview In this lesson, you'll learn how to do the following: