I'm looking into synchronizing an ebook in epub format (so the content is in XHTML) to an audio file. I'm thinking of putting something along the lines of:

<a class="audiolink" href="sound.ogg?t=1093"></a>

into the body of the document, and then have a custom epub reader that recognizes those tags and synchronizes the audio accordingly. That does seem like a bit of a hack to me though, especially the use of a special class name.

Does anyone have any pointers to how this may be done in a more standards-compliant manner (or somewhere where it has been done before)? Ebooks with audio annotation seem like an idea that may already be out there.