How To add Audio to my presentation

Hi:

My presentations only contains slides and each slide has a silent video associated with each presentation.

I usually create them using a program in PPT and then import them into Storyline.  I now would like to add audio to each of my sides.   The audio is just a description of the acutal slide.  Is it possible to add the audio during MS Powerpoint and it will import over or I must add the audio in Storyline ??

If I must add the audio in storyline or change the audio in storyline, how do I do this ???  The audio my be longer than my video (if that was the case, one can just listen to the audio before starting the video).  Any suggestions and the best way of doing this ???

Thank You,

Gary