Sound Across Slides in PowerPoint X for Mac

Follow these steps to loop a music or any audio file across slides in PowerPoint X 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 | Movies and Sounds | Sound from File menu option, as shown in Figure 2, below.
2. 
   Figure 2: Sound from file
2. Doing so brings up the Insert Sound dialog box that you can see in Figure 3, below. Locate the sound file you want to play, and click the Insert button.
3. 
   Figure 3: Insert Sound
3. When prompted if you want the sound on the slide to play automatically in the slide show, click the Yes button, as shown in Figure 4, below.
4. 
   Figure 4: Play the sound automatically
4. Ctrl + click (or right-click) the audio icon placed in the center of the slide, and choose the Custom Animation option from the contextual menu, as shown in Figure 5, below.
5. 
   Figure 5: Right-click menu
5. The Custom Animation dialog box will open with the Options tab active, as shown in Figure 6, below. Also, the inserted sound will be pre-selected as the object to animate.
6. 
   Figure 6: Custom Animation
6. Check the Play using animation order option, and choose the Continue slide show radio button. Also change the number in the Stop playing After text box to 999 slides. Check the box that says Hide while not playing if you do not want the audio icon to appear when you show the presentation. You can check the option to Loop until stopped option if you wish for the sound to repeat continuously, as shown in Figure 6, above.

Why 999 Slides?

You type 999 in the Stop playing After text box since that's the largest number that PowerPoint will allow you to add.
7. You can now adjust timing options for the sound. In the Custom Animation dialog box, select the Order and Timing tab. If you wish for the sound to play right when you open the slide, choose the Media entry under Animation Order that matches the one selected in the left pane, and press the Up arrow next to the list until the selected entry is on top. This ensures that the sound animates (plays) before any other objects do. Of course if you have no other animated objects in this particular slide, then the Up and Down arrow buttons will be grayed out, as you can see in Figure 7.
8. 
   Figure 7: Custom Animation
8. Also, under Start Animation, choose the Automatically, 0 seconds after previous event option. Doing so ensures that the sound begins playing as soon as you open the slide, or as soon as the previous object has finished animating if the Media object is not first in the Animation Order list (refer to Figure 7 above).
9. Click the OK button. 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.