Sound Across Slides in PowerPoint 2008 for Mac

Follow these steps to loop a music or any audio file across slides in PowerPoint 2008 on the Mac:

1. Navigate to the slide where you want the sound to begin playing, which is usually the first slide of the presentation. Then, choose the Insert | Sound and Music | From File menu option, as shown in Figure 2, below.
2. 
   Figure 2: Sound from file
2. In the resultant Insert Sound dialog box, navigate to the folder that contains the sound file you want to use. Locate the sound file you want to play on the slide, and click the Insert button, as shown in Figure 3, below.
3. 
   Figure 3: Insert Sound
3. PowerPoint will prompt you about how you want the sound to start, as shown in Figure 4, below. Click the Automatically button.
4. 
   Figure 4: Play the sound automatically
4. PowerPoint will place an audio icon in the center of the slide. Right-click (or Ctrl + click) the audio icon and choose the Custom Animation option from the contextual menu, as shown in Figure 5, below.
5. 
   Figure 5: Right-click menu
5. This action brings up the Custom Animation palette that you can see in Figure 6, below. Click the triangle next to Media Options to reveal the panel (refer again to Figure 6).
6. 
   Figure 6: Custom Animation
6. As you can see in Figure 6, above, we have changed the Stop playing After option to 999 slides since that's the largest number that PowerPoint allows you to type in.

Why 999 Slides?

You type 999 in the After text box since that's the largest number that PowerPoint will allow you to add.
7. Now, with the audio icon on your slide still selected, choose the View | Formatting Palette option, as shown in Figure 7, below.
8. 
   Figure 7: View menu
8. Doing so brings up the Formatting Palette as shown in Figure 8, below. Change the Play option to Across Slides, and check the Loop Until Stopped option as well.
9. 
   Figure 8: Formatting Palette
9. In all versions of PowerPoint, you might see an audio icon on the slide where you inserted the sound. If you don't like the icon on the slide, just drag it to anywhere off the slide, and your sound shall still play fine.
10. Save your presentation often.