I have proposed adding multiple sources separated by spaces here:
https://groups.google.com/d/msg/web2py/4tAElh1pqUM/wn-Lu1yvbeQJI think that audio or video souce lists could instead have this syntax:
[[title link1|link2|...linkn video]]
It requires simple string manipulation code in markmin2html, but I'm not sure it follows the markmin style. Bars are commonly used for separating table cells. Shoud markmin accept this way of listing sources?