Problems using Subler to convert MKV Files

Discussion in 'Apple TV and Home Theater' started by m021478, Feb 15, 2013.

  1. m021478 macrumors 6502

    Nov 23, 2007
    Trying to figure out how best to handle converting my MKV files into M4V files for playback on my Apple TV, iOS devices, and in iTunes on my Mac.

    Dealing with the video track seems easy enough... I just open an MKV file in Subler, then after clicking "Add", I highlight the video track and change the current profile to Main @ 3.1 to ensure that the remuxed file will play nice with whatever I'm trying to watch it on.

    The issue of audio tracks isn't quite as easy for me to figure out. The following blog post has the answer I am looking for, I'm just having a hard time interpreting some of the things the author si trying to get across:

    Let me start out by saying that I am using Mountain Lion, I do have Perian installed, and I have followed the instructions in the blog post to install the The Mountain Lion - compatible A52Codec.component (timestamp of Jul 27, 2012.)

    My goal is to have every MKV file I run through Subler be compatible with my AppleTV 3, my iPad 3, and my iPhone 5.

    "Convert AC3 Audio to AAC" checkbox in Preferences > Audio is checked (which I believe is necessary if I want to playback my remuxed files on iOS devices. In the preferences, what should I have the default settings be for "Downmix audio to:" configured for?

    For MKV files with multiple audio tracks, I think I am supposed to convert (remux?) DTS audio tracks into AAC - Dolby Pro Logic II, and for any Ac-3 audio tracks I am supposed to set the 'Action' to AAC - Stereo to ensure playback on iOS devices... is this correct?

    What am I supposed to do if the MKV file I am trying to remux only has one DTS audio track?

    Forgive my ignorance about all of this. I'm clearly not on the same level as all of you guys, but I'd still like to know how to deal with this scenario so I can use this tool to enjoy my MKV files in the Apple ecosystem.

    If possible, please keep your answers simple and straightforward. I just need to know the 'HOW', and not so much the 'WHY'... if you know what I mean.

    Thanks so much!
  2. mic j macrumors 68030

    Mar 15, 2012
    I would give the latest version of mp4tools a try (do NOT use any previous versions). Although Subler can be used to do what you want (with multiple steps to create the AAC and pass-through the AC3 track), mp4tools will create both audio tracks with very simple radio button settings. Also, Subler does not do DTS, while mp4tools does convert DTS to AC3.
  3. Pyromonkey83 macrumors 6502

    May 24, 2009
    Incorrect. Subler handles DTS converting just fine with Perian installed! It does not, however, support converting anything to AC3 as it is an AAC converter only.


    Convert it to AAC - Dolby Pro Logic II.

    Well... This would technically work, but it is wrong. If you want them to be compatible with all and yet still retain any resemblance of quality, Select AAC - Dolby Pro Logic II for any audio track you want to convert.

    Dolby Pro Logic (both I and II) IS Stereo audio. It also, however, has algorithms built-in to allow it to try and reproduce surround sound when hooked up to a 5.1 audio receiver. This is why it works with both the ATV AND iOS devices.

    I'd just like to point out that while you will get the answer you are looking for by doing what I say above, it is not your 1 stop-shop and you should really try to understand at least part of the "why". Without some form of understanding of all of this, you will just end up with problems in the end, especially if and when things change.

    Also, if you have a 5.1 audio system I would personally recommend converting audio to BOTH AAC - Dolby Pro Logic II AND AC-3 Surround sound. The AAC track would be used for your iOS devices and the AC-3 track would be used for your ATV using the 5.1 sound system. Of course if you don't actually care about audio quality or surround sound, then stick with the Dolby Pro Logic II AAC track and you will be fine.
  4. mic j macrumors 68030

    Mar 15, 2012
    Yes, you are correct on that. I was assuming DTS to AC3 was an OP need.
  5. sjk macrumors 6502a

    May 2, 2003
    For Apple TV 3 playback with audio output to a basic older model AV receiver (Onkyo TX-SR304), is conversion from DTS to AC3 preferable over multi-channel AAC to retain as much original audio quality and surround as possible?

    Using iFFmpeg with H.264 passthru and DTS to AC3 conversion (48 kHz, 448 kbps - maybe unnecessarily high?) from MKV input produces ATV3 compatible output. Listening tests still in progress.

    Wanted to ask about this before getting ambitious with more conversions. Thanks for any feedback.
  6. mic j macrumors 68030

    Mar 15, 2012
    Yes, convert to AC3. Multi-channel AAC is supported by very few AVR's.
  7. sjk macrumors 6502a

    May 2, 2003
    Seems to make the most sense.

    Yup, but this comment under AAC 5.1 Audio from Ten Myths of the Apple TV: 5.1 Audio got me wondering if/when it was reasonable to use anyway:

    "The Apple TV does something special with AAC 5.1 audio: it mixes it into a format Pro Logic receivers can split into multiple channels of sound, with a separate center channel and front and rear stereo."

    If still applicable (the article's nearly six years old, referring to the original Apple TV) I'm curious how that "something special" mixing compares with multi-channel AC3. Likely inferior, but more acceptable for mostly Apple-centric purposes.

    Conclusion: without direct multi-channel AAC decoding, multi-channel AC3 (with direct decoding) should have superior quality when converting from DTS.
  8. mic j macrumors 68030

    Mar 15, 2012
    Like your article said: it mixes it into a Pro Logic format that AVR's can split into multiple channels. The question to be answered is: Does your AVR have the ability to handle the format. Most don't, but try it and see. If it doesn't, there are ways to convert the DTS to AC3 Prologic which has wider compatibility and also provides a format that most (if not all) AVR's can synthesize to provide Prologic multi-channel audio.
  9. sjk macrumors 6502a

    May 2, 2003
    Hmm, I'm confused. That seems to contradict what the paragraph I quoted from also says:

    "All existing 5.1 receivers support Dolby Surround Pro Logic, which is why Apple is using it in its movie downloads and trailers. Pro Logic is also backwards compatible with regular stereo equipment."

    Mine certainly supports DSPL but not AAC 5.1 decoding.

    And earlier under Pro Logic Audio on Movies from iTunes:

    "The videos Apple currently sells in iTunes use Dolby Surround Pro Logic, a surround system which provides four discreet sound channels:

    •Stereo front left and right (for primary sound)
    •Mono center channel (for dialog)
    •Mono rear channel (for surround effects)
    Pro Logic systems with 5.1 speakers play the rear mono channel out both rear speakers, and send low frequency sound to the subwoofer, so the difference between Pro Logic and AC3/DTS content is not dramatic over the same set of 5.1 speakers."

    Not sure which of my limited iTS video collection that might be. Some displays "Dolby Digital 5.1" in addition to Stereo as Channels metadata in iTunes. Media inspector apps display the former as AAC format and the latter as drms. Is the latter multi-channel AAC?

    Finally, even earlier:

    "AC3 and DTS are two encoding systems for recording 6 channels of sound:

    •Stereo front left and right channels (for primary sound)
    •Mono center channel (for dialog)
    •Stereo rear left and right channels (for surround effects)
    •Subwoofer channel (for bass)"

    I thought that's what converting DTS (5.1) to AC3 (5.1) with iFFmpeg does. But converting to multi-channel AAC (processed with DSPL on my receiver) doesn't seem like it would suffer much. And I'd think newer AAC encoding could have comparable audio quality with smaller size and future compatibility with direct/discreet AAC channel decoding.

    Thanks for your time and patience helping me better understand this.
  10. dynaflash macrumors 68020

    Mar 27, 2003
    Yes, use AC3 5.1. All atv's downmix aac 6 channel discrete to a strange 3.0 mix. Use AC3 5.1 just as the HD iTunes stuff uses.
  11. mic j macrumors 68030

    Mar 15, 2012
    Well, I new there was a glitch somewhere using AAC 6 channel. Thought it was with the AVR but, I was mistaken. Sorry for introducing all that confusion. :eek:
  12. dynaflash macrumors 68020

    Mar 27, 2003
    NP, doesn't matter even if you have one of the few avr receivers that can decode aac six channel discrete, that is not what the atv will send out.

    Anecdotal: Before appletv take 2 software ( on the original atv 1) HB devs heard rumors of true 5.1 audio output but had no specifics. Hence HB developed the aac 6 channel discrete output in anticipation of it working on the forthcoming new software presuming it had to use aac which to that point was all the atv could put out (in 2 channel dpl2). However once Take 2 (as it was called) came out ... voila ... it was AC3 5.1 passthru. So a swing and a miss on HB's part. Course then HB came out with the "magic sauce" of 1 track of 2 channel dpl2 and the 2nd track in AC3 5.1 . which worked! Thankfully apple had that intro movie when the atv 1 boots up. HB devs got it off of the atv 1 and reverse engineered the audio layout. So there is a bit of history for you, not that anyone really cares. :)
  13. sjk macrumors 6502a

    May 2, 2003
    Bypassing the possibility of downmixing is a good enough reason to choose AC3.

    Ultimately helpful confusion, if any. :)
    I should be the one apologizing for some gravedigging here.

    Good point to remember.

    It's interesting to me. :)

    Last question (for now): Should iFFmpeg be sufficient for my relatively simple DTS -> AC3 conversions or is there a better tool? Popular ones use ffmpeg or the same libraries it does so it seems more a matter of picking a UI.

    Thanks again!

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