Progress Bar for QuickTime Movies

Date:    Tue, 20 Jun 1995 13:54:15 -0800
From:    KEVIN BAIRD <kevin_baird@QMAIL.LIGHTSPAN.COM>
Subject: digital video progress bar
Yes, I've recently done something like that. This lingo controls movieRate instead of movieTime of a QuickTime movie, which is what you want. But it should be pretty similar. The dragBall handler is called by a click (mouseDown) on both the "thumb" and the line the thumb is constrained to, and it's pretty responsive. The position of the ball is determined constantly by whatever the current movieRate is, and the movieRate is affected immediately by dragging the ball. I haven't tested it with high datarate movies, though. The fun part is that it's really easy to modify the min and max values of the rate, and that moving the controller doesn't break it, because there are few numbers hard-coded in. It uses a (unoptimized) linear funtion to convert from pixels to rates and back. (I even made the sprite numbers global because I was rearranging it on the score a bunch, and got tired of changing 3s to 2s and so on.) The setBall handler is called by Play (setBall 1) and Pause (setBall 0) buttons. A backwards button would be setBall -1. Hope it helps. 
on setMooVSpeed newRate
  global gsMooV, gsSlider, gsBall
  set the movieRate of sprite gsMooV to newRate
  set the text of cast "fSpeed" to string(integer(newRate * 100)) & "%"
end setMooVSpeed

on dragBall
  --  drag ball to determine and set movieRate
  global gsMooV, gsSlider, gsBall
  repeat while the stillDown
    --  drag the ball
    set ballLoc to constrainH(gsSlider, the mouseH)
    set the locH of sprite gsBall to ballLoc
    updateStage
    --  figure the new speed
    set scale to 4.0  --  0 to 4
    set slope to scale / (the width of sprite gsSlider)
    set newRate to slope * (ballLoc - (the left of sprite gsSlider))
    setMooVSpeed newRate
  end repeat
  --  updateStage
end dragBall

on setBall newRate
  --  click something that sets movieRate, then update ball.
  global gsMooV, gsSlider, gsBall
  set the locH of sprite gsBall to (the left of sprite gsSlider) + newRate * (the width of sprite gsSlider) / 4.0
  setMooVSpeed newRate
end setBall