MKVTools AC3 6ch. to aac 5.1

Discussion in 'Apple TV and Home Theater' started by iYannickV, Mar 15, 2011.

  1. macrumors newbie

    Mar 15, 2011
    I’m using MKVTools to convert my MKV’s to MP4, but I’m experiencing some difficulties.
    When I convert a MKV with an AC3 6ch. Audio track to an mp4 with AAC 5.1, the movies plays fine in iTunes but when I want to see it on my iphone or Appletv via airplay the movie won’t play.
    What am I doing wrong?
  2. macrumors regular

    Jun 14, 2010
    I use MKVTools as well to convert MKV to M4V.

    I used to have similar audio problems streaming to ATV2, but I think with Apple's latest updates to iTunes and AppleTV2, I don't have those problems anymore with AC3 audio on ATV2! So I just select pass thru for audio in MKVTools when the source is AC3.

    AAC 5.1 works fine on ATV2 as well, but I've read in this forum somewhere, that ATV2 will downmix AAC 5.1 to two-channel audio, while ATV2 will just pass thru the AC3 audio to an audio receiver that is capable of handling AC3 audio (i.e. no downmixing). I don't have a digital audio receiver yet, so I can't confirm this, it's just what I read somewhere.

    Do you have ATV2 and iTunes with the most updated version?
    Also, make sure your video is maximum resolution 1280x720 for ATV2.
  3. thread starter macrumors newbie

    Mar 15, 2011
    I think something goes wrong during muxing.
    I used Subler to mux the .h264 video file and the .aac audio file that MKVtools spits out.
    This seems to work. I can view the video via airplay on my iphone. Didn't have a change to test it with an atv2.
  4. macrumors regular

    Jun 14, 2010
    Why not let MKVTools mux them together and let it create the M4V file? Thats what I do. I only use Subler to add metadata and subtitles.

    I am only muxing in a single audio track not two audio tracks, like some other people do. Having multiple audio tracks might cause issues with ATV2 and the latest ATV2 update.

    Also, because of this latest update, you might have to check your TV's HDMI settings are set up correctly (e.g. audio signal is digital vs analog), when before they didn't matter as much.
  5. thread starter macrumors newbie

    Mar 15, 2011
    I used subler to test something. When MKVTools mux the files the movie won't play on my iphone. When I check the information of the video fille after the muxing, iTunes says the audio had a bitrate of 0 kbps.
    Then I used the same video and audio file with Subler and this works perfectly.

    So I find verry strange what goes wrong during the muxing with MKVTools.
  6. macrumors 6502

    Jun 14, 2010
    Also: why are you transcoding the audio to 5.1-channel AAC? The Apple TV can't play it without downmixing. Neither can the Mac unless you have an external sound card.

    The best thing to do is leave the AC3 track intact and add a 2-channel AAC track. This is the format iTunes HD movies use and it works perfectly with the Apple TV.
  7. thread starter macrumors newbie

    Mar 15, 2011
    Thnx for the tip. I just tested it, and the movie plays fine on my iPhone with airplay. But is there a way to give the audiotracks a name?
  8. macrumors regular

    Jun 14, 2010
    I still don't understand the need for two audio tracks (unless for multiple languages) in a movie file. Could someone explain this? You can change the name of an audio track in Subler. I stream via Home Sharing or sync HD movies from my iTunes library to my iPhone4, and they play with no problems either way. Yes, they take up more space in my iPhone when I sync them, but when I am done watching I remove them (I am also glad I invested in the 32GB).
  9. macrumors 6502

    Jun 14, 2010
    The Apple TV can play 5.1-channel Dolby Digital (AC3), which gives you proper surround sound if you have a multichannel system setup. The iPhone etc can't play AC3, it can only play stereo AAC. So you put in a 5.1-channel AC3 track and a 2-channel AAC track in the same file if you want to play the same movie on both the iPhone and the Apple TV and take advantage of the maximum capabilities of both. They each know which track they're supposed to play.
  10. macrumors regular

    Jun 14, 2010
    thanks for the explanation! since the latest updates, i just started to use AC3 audio only on my m4v files instead of AAC 5.1. And they play fine on ATV2. I believe I tried it on my iPhone too and thought they played with sound fine as well, but let me re-check that tonight. If it is like you say, then I'll mux in the second AAC 2-channel track. I'll keep you posted.
  11. thread starter macrumors newbie

    Mar 15, 2011
    owke, I successfully added 2 audio tracks. But when I wanted to add subtitles with Subler the movies plays both audio streams at the same time in Itunes.
    If I click the speech bubble, it gives me only the option to turn of the subtitles.
    This is how I do it: first I convert the MKV with MKVTools, I check the pass thru for video and audio and check the add 2ch. track. This works fine. Then I put the m4v that coms from MKVTools in Subler and add the .srt file.

    Am I doing something wrong?
  12. sampdoria, Mar 15, 2011
    Last edited: Mar 15, 2011

    macrumors regular

    Jun 14, 2010

    re: the audio tracks. what's wrong with both streams playing, maybe that is supposed to be that way?
    check your itunes preferences, for any audio setting that may be triggering that, or rename one of the tracks differently in subler, so that itunes is able to distinguish them separately and lets you choose one from the other. sorry i'm not home to check all of this first hand, and i don't have much experience with multiple audio tracks.

    also try muxing (not burning) the subtitle file using MKVTools if subler is giving you trouble. i've had better results muxing in subtitle files with mkvtools than subler about 50-50.
  13. macrumors regular

    Jun 14, 2010
    Ok, well I was mistaken. My movie files with AC3 audio won't play on my iPhone. :( Also no sound is played on my Windows XP desktop when playing them through iTunes or Quicktime. Though VLC player plays them just fine. When they stream to the ATV2, everything is fine too. And when i play them on my MacBook Pro, movies with AC3 also play fine (the Mac must have an AC3 codec converter). So now I understand that I'm going to need a 2nd audio track in my movie files as AAC 2-channel in order to play on my iPhone and my Windows XP machine. Does anyone know of any of an AC3 plugin for Quicktime in Windows XP? I'll mux in the 2nd audio track as AAC 2ch and let you know if that does not solve it for me.
  14. thread starter macrumors newbie

    Mar 15, 2011
    Everthing works perfectly now. I did some research in the Subler issues and you need to put the 2 audio tracks in an alternate group and then the subtitle in an other alternate group.

    Now when I click the speech bubble in iTunes, I can choose between the audio trakcs and to turn the subs on or off.

    The movie plays great in iTunes and on my iPhone.

    The only thing for me to do now is to convert my massive movie collection :p
  15. macrumors regular

    Jun 14, 2010
    Congrats and thanks for this, I didn't know about alternate grouping either, and you probably saved me hours of time trying to figuring this out. So:
    Video Track in Alternate Group: None
    Both Audio Tracks (multi-channel AC3 and 2-channel AAC) in Alternate Group: 1
    Subtitle Tracks in Alternate Group: 2​

    Thanks to peterjcat for explaining this too!
  16. thread starter macrumors newbie

    Mar 15, 2011
    No problem, I'm glad I could help.
    And yes, that's how I do it and it works perfectly!
  17. macrumors regular

    Jun 14, 2010
    Yes it does...It took about 15 minutes to remux the audio in MKVTools (not bad). Now all my devices (Mac, PC, ATV2, and iPhones) play movies just fine. This will be my set-up from now on using MKVTools and Subler! to set up chapters :eek:.
  18. thread starter macrumors newbie

    Mar 15, 2011
    I've been looking into this to. You can put 2 types of chapter files in subler.
    Subler - ChapterTextFormat
    The only problem is finding these chapter files. I've been not able to find them.
    I can make them myself but I don't want to put al the time and effort in something I probably won't use.
  19. macrumors 6502a

    Aug 1, 2004
    The AppleTV2 can NOT play AC3 6ch though. On my ATV2, it sqawks and the movie freezes.

    I just convert to AAC (2Ch.)

    Does the "add 2 Ch. track" add an AAC (2Ch.) track?
  20. macrumors 6502

    The Mad Hatter

    Oct 12, 2004
    I don't know about your ATV2, but mine plays AC3 6-channel discrete fine.
  21. macrumors 68020

    Feb 19, 2011
    And that's when ATV2 is connected to your receiver right?

    Yes, yes it does.
  22. macrumors 6502

    Jun 12, 2007
    Unless something has changed, the ATV2 will play AAC 2 channel natively, but only pass-through AC3. The ATV2 isn't playing the AC3, the device on the other end of the cable is. So, if your TV or receiver doesn't support AC3 5.1, or have the ability to down-mix it to stereo, you won't hear anything.
  23. macrumors 6502a

    Aug 1, 2004
    Wirelessly posted (Mozilla/5.0 (iPhone; U; CPU iPhone OS 4_0_1 like Mac OS X; en-us) AppleWebKit/532.9 (KHTML, like Gecko) Version/4.0.5 Mobile/8A306 Safari/6531.22.7)

    I'm using the 1/8 stereo out jack on the back of the apple TV.

    I guess the stupid appletv2 doesn't transcode the ac3 5.1 down to two channel stereo hence the need for another track.
  24. macrumors 6502

    Jun 12, 2007
    It should work fine if you switch an optical cable for the stereo jack, as long as your receiver can handle Dolby Digital 5.1 audio.
  25. macrumors 65816


    Dec 10, 2002
    Open file with Subler. Click the video track. Change profile to mid 3.0 instead of high profile >3. Regardless of the other things, this is the most important.

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