Captivate's Preloader feature allows you to both control what the learner sees as they wait for the lesson to begin playing, and the percentage of the lesson that must be downloaded before the lesson will begin to play.
Captivate ships with a few Preloaders you can use when you publish your lesson. However, many of my corporate customers prefer to brand the lesson and use their corporate logos as the Preloader. You can accomplish the task easily enough. First, with a project open, display Captivate's Preferences (Edit > Preferences for Windows users; Adobe Captivate > Preferences for Macintosh users). Then select the Start and End category from the Project group.
To load your corporate logo and use it as a Preloader, click the Browse button to the right of Preloader. Find and open your logo. You can use any of the following formats as a Preloader: jpeg, gif, bmp, wmf, or swf.
To control how much of the lesson must be downloaded before it will begin to play, change the Preloader % value. The higher the Preloader percentage, the longer the learner will have to wait before seeing the lesson. If you set the Preloader % lower, the lesson will play sooner. However, since little of the lesson will have been received by the learner, the lesson with sputter along instead of playing smoothly. If you set the percentage too high, the learner will have to wait for the lesson to begin playing at all. A best practice would be to set the Preloader somewhere in the middle. I typically set my Preloader % to 50, which tends to work quite well.
Once you publish your lesson, the Preloader image will appear for your learners until the Preloader % is reached.
If you'd like to see a demonstration on adding a preloader to a Captivate project, check out the video I created on IconLogic's YouTube channel.