Back in October, upon publishing my tutorial (link) on fixing videos no longer playable in most iOS video players, the then-current version of the tool to be used, MKVTools, wasn't still able to add an AAC track in addition to the original AC3 one without human intervention. (Just to recap: AAC is the iOS-friendly audio format and AC3 is the format that is no longer supported in almost any third-party iOS multimedia players, “thanks” to Dolby's forcing developers to drop the support.)