Step 3 of the addSourceBuffer algorithm says: "If the user agent can't handle any more SourceBuffer objects then throw a QUOTA_EXCEEDED_ERR exception and abort these steps."

We would like to add an informative note describing what we think will be a common restriction in initial implementations:

"For example, a user agent may throw QUOTA_EXCEEDED_ERR if the media element has reached the HAVE_METADATA readyState."

Today, many media engines expect to process all the metadata for a presentation at the beginning before indicating they have all the metadata. Allowing dynamic changes to this will require more work.