Re: Question about CoreAudio, digital output out and multichannels audio
Re: Question about CoreAudio, digital output out and multichannels audio
- Subject: Re: Question about CoreAudio, digital output out and multichannels audio
- From: Brian Willoughby <email@hidden>
- Date: Thu, 03 Mar 2011 17:13:50 -0800
Are you aware of the Hog Mode feature of CoreAudio? Have you
researched the various API specifications and example source code?
It seems like you have a very long list of desired features, but all
of them are possible with CoreAudio.
The CoreAudio HAL presents information and access to the raw audio
device. If a device only supports 2 channels or 8 channels, then the
HAL API will allow your program to discover this. If you select 8
channels but only need 6 channels, there is a CoreAudio API to
disable the unneeded channels to save CPU.
Channel ordering also has a method in CoreAudio for changing the
order, but some user input is required. For example, not every
output system follows the SMPTE standard, so the user must use Audio
MIDI Setup to configure their speakers. If you can discover the
channel ordering in your media source, along with the channel
ordering of the specific output hardware that your user has
connected, then you can use CoreAudio to rearrange the channels to
match - but the process is not automatic because too much information
is missing.
You might not find anyone willing to take the time to volunteer and
look at your source code unless you get into specific API questions
that are not covered by the example source.
Brian Willoughby
Sound Consulting
On Mar 1, 2011, at 23:15, Jean-Yves Avenard wrote:
Now, with CoreAudio I'm running into heaps of problem.
When multi-channels audio however, not quite.
when using the DisplayPort -> HDMI adapter (with audio support
obviously).
In either analog or digital mode :
The AudioDeviceID only reports 2 and 8 channels as being available
Is it expected for CoreAudio to only supports explicitly those? or
can I assume that if 8 channels is supported then anything in
between is also supported? (in particular 6 channels)
Something I've noticed too, is that the channels ordering isn't
following SMPTE standard.
the SMPTE standard is:
L R C LFE Rls Rrs LS RS
with CoreAudio, when I do get audio out it is:
L R C LFE LS RS Rls Rrs
Is this expected ?
Is the channel ordering used by CoreAudio documented anywhere?
For TrueHD or DTS-HD ; I get no-where whatsoever, it's like I
didn't write anything on the audio card.
Is HBR audio bitstream something that is supported; or at least
will be supported in the near future?
Is there a way to set the IEC digital flag so I can try getting
around any of such limitation should they exist?
BTW, the source code is publicly available there:
https://github.com/MythTV/mythtv/blob/master/mythtv/libs/libmyth/
audio/audiooutputca.cpp
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