The bug occurred when the underlaying GStreamer backend of Qt Multimedia was returning an infinite duration for the video. The timeline of the video controls was shown but was unusable (seeking broken for example). It's better to hide it rather than a broken state.
Created attachment 89398 [details] Proposed patch.
Comment on attachment 89398 [details] Proposed patch. Ok.
Comment on attachment 89398 [details] Proposed patch. Clearing flags on attachment: 89398 Committed r83804: <http://trac.webkit.org/changeset/83804>
All reviewed patches have been landed. Closing bug.