thank you for the interesting pointers. They all look promising.
Just to clarify my request: I do not want to create a media-overlay, because I am working with several different audio clips whose reproduction should be left on the user's will.
I was just asking if it was possible to "tweak" the <audio> tag in order to have it displayed in the same way on every reading software (a way to achieve this might exploit the epub:trigger, I will give it a try tomorrow) and whether it is possible to automatically stop an ongoing audio clip if the user exits the chapter it belongs to.
Thank you again for your suggestions!