Re: Outputting Multichannel sound via HDMI - revisited
Re: Outputting Multichannel sound via HDMI - revisited
- Subject: Re: Outputting Multichannel sound via HDMI - revisited
- From: Brian Willoughby <email@hidden>
- Date: Sun, 12 Dec 2010 01:47:33 -0800
This list is for discussions of CoreAudio API programming. You seem
to be bouncing around between application software feature requests
and API support, or at the very least you do not seem to have a
clearly appropriate question. Basically, the only question you're
going to get answered here is whether it is "possible" to do what you
want when writing a CoreAudio-based program, and how to do it. If
it's possible, but not currently implemented by the free software
bundled with Mac OS X, then you need to look elsewhere for feature
requests as an end user. Apple's mission is not to provide every
possible feature that end users might want - there are still a few
opportunities left unimplemented for third-party developers to provide.
A quick check seems to indicate that CoreAudio supports decoding of
AC3 formatted data. Whether or not this works with multichannel
sound is one appropriate question. If the answer is positive, then
perhaps you should try to write a CoreAudio program which pulls AC3
data from a DVD, uses CoreAudio to decode it, and then sends the
multichannel data to a CoreAudio-compliant audio device. There are
various pieces of CoreAudio, such and AudioFile, ExtAudioFile,
AUAudioFilePlayer, AUHAL, and AUGraph, which are available for this
task, but I don't think you're going to find a single object which
handles the combined task of reading AC3-encoded audio tracks from
DVD and playing them directly to a device such as the HDMI
interface. For one thing, DVD audio is interleaved with DVD video
data, and extracting the audio from the MPEG stream is outside the
realm of CoreAudio.
This is all fascinating technology, and as an end user I would like
to be able to play a DVD in surround from my laptop when it is
connected to any of a huge variety of multichannel audio interfaces,
but I still recommend that you ask focused questions which are
relevant to this list. I realize that I have, at times, strayed from
the CoreAudio topic in my own postings, so please take this as a
constructive and friendly suggestion.
P.S. I think that Paul used the word "frequency" to refer to how
often releases appear on the market - I don't think he was saying
anything at all about 44.1 kHz versus 192 kHz.
Brian Willoughby
Sound Consulting
On Dec 11, 2010, at 23:50, Simon Thorpe wrote:
On Sat, December 11, 2010 18:52, Paul Davis wrote:
On Sat, Dec 11, 2010 at 12:00 PM, Simon Thorpe
<email@hidden> wrote:
I was reading along with interest until we got to here:
But, now that I can potentially output 7.1 channel audio, I'm pretty
much
stuck because of the fact that multichannel audio recordings that
can be
played on a Mac are effectively non existent. iTunes will
happilly play
multichannel recordings but the only stuff you can buy from the
iTunes
store is stereo. Other sources such as Spotify, Deezer etc are all
stereo
only. If anyone knows of a place where I can get hold of
multichannel
recordings, I'm definitely interested...
So you're only interest in this is (a) 7.1, a not very good
multichannel format invented primarily to generate licensing revenue
and (b) playing back existing recordings?
What made you think that people release multichannel recordings with
any notable frequency whatsoever?
I don't care at all about frequency - at my age, 44.1KHz is
probably just
fine! No, the problem is that I can't even play the 5.1 Dolby Surround
Sound tracks on my DVDs using Apple's DVD player! In the DVD menu,
I can
choose different audio formats (Stereo, Dolby 5.1 surround sound)
but when
I've selected 8channels in Audio Midi Setup, it just comes out as
stereo.
And if I select Encoded Digital Audio, there is no sound at all.
Yes, I know that it is (just) possible to output AC3 encoded
signals via
an optical link
(http://www.cod3r.com/2008/02/the-correct-way-to-enable-ac3-
passthrough-with-quicktime/
). But this hack doesn't work with the 8channel HDMI option. By the
way,
I've tried with and without Perian installed (http://
www.perian.org/ ) -
nothing seems to work.
So, let's forget about fancy 7.1 recordings. How about being able
to play
the hundreds of thousands of DVDs with Dolby surround sound?
Currently, I
have to use a stand-alone DVD player to play them.
It seems to me that having a bit of code built into CoreAudio that can
read AC3 encoded audio tracks and play them through the 8 channels
available via HDMI is the strict minimum.
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