The spec was updated to require a 'progress' event just before the 'load' event: Once the entire media resource has been fetched (but potentially before any of it has been decoded) Queue a task to fire a progress event called progress at the element. http://html5.org/tools/web-apps-tracker?from=3618&to=3619
Created attachment 35047 [details] proposed patch
http://trac.webkit.org/changeset/47431