metadata element or sync:link element?

[iherman]

At the moment, that element is fairly underspecified; it comes that way from the SMIL specification. The problem I see is that the metadata element relies on the inclusion of other types of metadata coming in XML. That may have been a reasonable assumption in 2008 (when the latest version of SMIL was published) but may not be today. How would I use schema.org statements?

I wonder whether it is not better (while keeping metadata for SMIL's sake) to introduce a sync:link sub-element, whose only purpose would be to link to an external metadata file, in whatever format. That would follow the approach used in EPUB.

[marisademeglio]

This seems entirely reasonable to me. We haven't come across use cases involving metadata, so that aspect is definitely underspecified.