Jenpen

Hello, I"m new to this, so please excuse any ignorant questions! I've been using Switch to convert wav files into mp3s for my digital store. All great! Now, i'm developing an ebook, but in an enriched format which has embedded audio in it in some sections. Not sure how to convert my audio files into a format, using Switch so they can be played within the ebook, in all devices such as iPhone and iPad. I checked with a publishing services company and they require audios to be in mp4 format... How do I make the audios into mp4 format? I think this is the format required.. Cheers, Jenny