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.)
Answering a related question (thread) over at MacRumors (where there are a lot of, because of Dolby's actions, disgruntled users in the forum), I've quickly tested the recently-released beta 5 (download from HERE – do NOT get the non-beta, non-recommended, old one!) version and found out it has also fixed the two-channel AAC addition problem.
Now, it's really easy to make a (single) MKV have an AAC audio track – in addition to the original AC-3. (I recommend keeping the latter so that you always have a real 5.1 audio track in your file.) Just
- drag-and-drop the file in MKVTools (here, I used the one HERE, linked from HERE)
- select all tracks (by clicking the A + S + V buttons – the upper left annotation in the screenshot below)
- select the “add 2-Ch. track” checkbox (the other annotation in the screenshot)
- click “Convert” in the lower right corner:
(as with all the other image thumbnails here, click for the original image!)
What about the batch mode?
Should you want to convert several MKV videos at a time, absolutely automatically, I have some bad news.
In batch mode, you need to use pre-defined presets. It's only there that you can change the transcoding parameters. Unfortunately, it lacks the checkbox for adding a two-channel AAC audio track. The following preset shows one that just copies the video and the AAC (stereo) audio / embedded subtitle tracks (if present) and also copies the AC-3 track (denoted as “Surround”; also see the bottom right annotation):
(Also note that I've annotated the “Add Preset” button and the preset name. Upon first clicking the “Edit” button on the main dialog, you'll want to click the former (“Add Preset”) so that you can define a new one by not overwriting anything else. I've chosen a name reflecting what the preset does; it must be entered in the “Name” textfield – the second annotation.)
You can easily make this preset the one to be used in batch mode (too) by clicking the drop-down list just under the “Settings” label with the Edit button. I've annotated it in the following screenshot:
Note that, above, I've also annotated
1, the “Edit” button (see above – it's the one you'll need to click to be able to add/ edit presets)
2, the “Track Selection” preset, where I've selected “All Tracks” instead of the default “Manual” one.
Unfortunately, when you select an active Settings preset and, then, try to enable the “add 2-Ch. track” checkbox (as you would do in non-batch mode; see the first section), the active Settings preset changes back to “Manual”, which means you won't be able to mass-convert in batch mode.
I really hope the developer adds an “add 2-Ch. track” checkbox also in the preset setting dialog. Until now, you'll need to use the non-batch mode of MKVTools; that is, you'll need to add an AAC track one by one.
Of course, if you don't need to keep the AC-3 track in the target MKV, only an AAC one, you can use the batch mode. Then, the preset setting should be as follows (also note the different preset name (up the “Name” textfield) reflecting the custom parameters):