AAC 5.1 surround sound on AppleTV

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Level 1

3 points

AAC 5.1 surround sound on AppleTV

Hi there,

I recently became a user of FCPX and I do my videos now with 5.1 surround sound. Exporting the video from FCPX will result in a mov file having typically H264 HD video and AAC 5.1 as audio. So far so good, but when streaming on my AppleTV 2 I noticed that AppleTV 'decodes' the AAC audio to provide a downmixed stereo PCM audio on the optical interface and does not transcode the stream to DTS or AC3. Neither does it provide 6 discrete audio channel on the HDMI interface to allow to connect to a hometheater amplifier for true multichannel decoding.

My question: does AppleTV 3 support multichannel AAC and transcode to multichannel DTS or AC3 (via the optical audio interface) or alternatively does it support the decoding to 6 discrete PCM channels via HDMI ?

If not, is a firmware upgrade in the pipeline to support multichannel AAC ?

Many thanks for the info

Regards

Steve

iMAC

Posted on Oct 22, 2012 2:23 PM

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Answer 1

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Alley_Cat

Level 7

20,548 points

Oct 22, 2012 3:12 PM in response to slacha1

AppleTV has never officially supported 5.1 AAC only Dolby Digital 5.1.

The majority of amps/receivers do not support AAC, and AppleTV AFAIK has never transcoded on the fly to 5.1 Dolby Digital.

Stereo audio AAC/WAV/Apple Lossless etc get converted by ATV2 and 3 to stereo linear PCM for optical output at 48 kHz (yes not 44.1 kHz even for CD) 16 bit.

Dolby Digital 5.1 is output as is, as a bitstream for decoding by an amp/receiver.

Not sure what AppleTV is doing with your 6 channel AAC - it may simply be using the L and R channels and discarding the rest or downmixing to 2 channel.

There is no official word on this.

The only officially supported specs we know of are:

ATV3:

http://www.apple.com/appletv/specs.html

ATV2:

http://support.apple.com/kb/SP598?viewlocale=en_US&locale=en_US

AC

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