Watch the video tutorial covering timeline controls

The timeline/playhead work in combination to show users where they are in the video and allows them a control to scrub back and forth.

Create a timeline by creating a MovieClip of arbitrary length and giving it an instance name of timeline. When the file is published the timeline will not move.

You can create the playhead anywhere on the stage and it will snap to the beginning of the timeline at runtime. When snapping the playhead will center itself vertically on the timeline and move to the right as the video plays. The user can click-hold on the playhead to drag it across the timeline.

The downloadProgress bar is not necessary for the playhead to function but it does give the user an indication of how much of the video has been downloaded and therefore how far they can scrub forward in the video - obviously, you cannon scrub past the point that the video has been downloaded.

Because the downloadProgress bar will be shrunk and stretched to display the amount of the video stream that has been downloaded I would recommend not using a line for the MovieClip. Rather it works best if you create a rectangle with no border because the border will become distorted.