make it possible to query the AVOfflineComposition.errorString in the case where AVOfflineCompositionFailedNotification notification is delivered
rework logic that decodes h264 to mvid before comp op so that a tmp file is used as an intermediate in case of a crash, also cleanup the tmp file is writing fails due to disk being full
force all CoreText render operations to sync to the main thread to avoid any chance of a crash in typesetter code