What is the diff between AC3 and AC3 Passthru? And why won't they work on ATV2?

Discussion in 'Apple TV and Home Theater' started by marcel-v, Dec 27, 2010.

  1. marcel-v macrumors regular

    Oct 25, 2006
  2. akm3 macrumors 68020

    Nov 15, 2007
    AC3 is just the codec name for Dolby Digital 5.1

    They SHOULD work on ATV2
  3. Cave Man macrumors 604

    Cave Man

    For the Apple TV, audio track 1 must be AAC and audio track 2 must be AC3.
  4. NightStorm macrumors 68000

    Jan 26, 2006
    Whitehouse, OH
    I assume you are talking about options in the latest handbrake nightly builds...

    "AC3 Passthru" will take an existing AC3 soundtrack and include an exact copy as a track in the final encode.

    "AC3" will take a non-AC3 source (ex. DTS for a DVD or Bluray) and convert it to AC3. This is useful for devices that do not support other formats (ex. AppleTV).

    Both options will create audio tracks that are compatible with the AppleTV. There is likely something else about your encode causing your problem.
  5. dhy8386 macrumors 6502a

    Aug 13, 2008
    I am not sure how you mean that but i have 300 m4vs i encoded with handbrake with the 1st audio track selected being the AC3 track and the second audio track being the AAC track. Works fine in ATV2 as well as on iPad or iPhone
  6. newagemac macrumors 68020

    Mar 31, 2010
    But are you getting 5.1 surround sound that way? It's supposed to be the other way around.
  7. Cave Man macrumors 604

    Cave Man

    The ATV software looks for AC3 in track 2. If it's there, then it enables AC3 passthrough via the optical port. By default, track 1 is enabled and is AAC, AC3 is disabled and is track 2.

    Attached Files:

  8. dhy8386 macrumors 6502a

    Aug 13, 2008
    On every file. I did not know that "it was supposed to be the other way around". What does that mean? Your saying the ATV2 cant play a AC3 track that is listed as track 2?

    I have converted MKVs, Blu Rays (which go to MKV then to handbrake), DVDs and AVIs. My preset it the 5.1 track first followed by the AAC track. Whether its passthru or DTS conversion, I have never had a problem with one file.
  9. Cave Man macrumors 604

    Cave Man

    The reason the Apple TV preset in Handbrake sets track 1 to AAC and track 2 to AC3 is because that's how the files from Apple are. Handbrake just replicate's Apple's videos for the Apple TV.

  10. PurdueGuy macrumors regular

    Jun 23, 2010
    Those requirements on that support page are "should" and not "must" nor "shall."

    Putting them in a different order doesn't violate the spec, and "should" work, but YMMV.
  11. dhy8386 macrumors 6502a

    Aug 13, 2008
    So if you set the dolby digital to audio, i believe if the AC3 track is track 1, it will not pick it up and instead play stereo. However, i am not sure why you would never set it to on instead of auto, which is how i have it, and this it works regardless of how it is encoded - track 1 or track 2. That said, no reason for me to not switch it from this point on in case something changes.

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