There are two ways to playback your audio once you have attached it to a presentation and changing it to a Slidecast:

1. You can divide audio equally between the slides (default setting)
2. You can synchronize each slide with a point in the audio file

To create a Slidecast, please follow the steps below: 

Step 1: Upload your presentation file to SlideShare or find an existing existing presentation on SlideShare that you wish to turn into a Slidecast.

Step 2: Visit your 'My Uploads' page and click on the 'Add audio' link.

Step 3: Click on the orange 'Upload mp3 file..' link to bring up an explorer window that will let you search for your audio file

Step 4: Once the audio has uploaded and converted, you can then synchronize slides and audio — here are the three ways to do this:

• You can leave the audio un-synchronized. (As long as you do not adjust the audio this is the same as the 'divide audio equally' option)
• You can do a quick sync using the divide audio equally (suited to musical presentations)
• You can manually sync each slide to a particular point in the audio file for custom timing