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: Jean-Yves Avenard <email@hidden>
- Date: Fri, 04 Mar 2011 12:28:44 +1100
Hi
Thank you for your answer.
On 04/03/2011, at 12:13 PM, Brian Willoughby wrote:
> 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.
I am aware of the hog mode ; and this is what I use for digital audio bitstream.
When going through the list of "ac3" streams ; they only ever support 2 channels, and a maximum of 96kHz. This makes it impossible to bitstream any of the new audio stream like E-AC3, DTS-HD or TrueHD. When the hardware does support it.
What the hardware actually support is never reported as such; only a limited subset.
>
> 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.
which I also already use.
>
> 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.
I was hoping to do by code what the Audio MIDI setup application is doing.
In particular configuring the number of channels. By default, even when you plug a hdmi device, the default is always stereo audio, even when you configure the frame to have 8 channels ; just means you're only going to hear the left and right audio channel
>
> 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.
>
This isn't what I was looking for at all. I was just asking if anyone was familiar with any of the problems mentioned.
And obviously none of the example source actually do any of the features I'm trying to get to work
> 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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