Re: 5.1 Surround-to-stereo AU (Brian
Re: 5.1 Surround-to-stereo AU (Brian
- Subject: Re: 5.1 Surround-to-stereo AU (Brian
- From: Ernest Burghardt <email@hidden>
- Date: Fri, 6 Feb 2009 14:38:41 -0800
Hi Brian,
Thank you for the enlightenment, it is unfortunate, the AU sounded like it would be such an elegant solution.
I will search the archives for the examples you mention, which are what I originally expected I would have to do.
I was a little mislead by the OutputUnits>AUHAL>HAL>IOKit flow into thinking that I could do an AU as a "user-mode driver"...
Ernie
On Fri, Feb 6, 2009 at 2:06 PM, Brian Willoughby
<email@hidden> wrote:
Ernie,
Now that you've explained your goal more clearly, I don't think an AU is appropriate. The advantage of AudioUnits is that you can use them in applications that you have not written yourself. It is a plugin format. Surround down mixing is already at a disadvantage at the moment, here, because there are no hosts which know what to do with a down-mixing plug-in.
In your case, you need to build a fake audio device driver. Instructions for this can be found in the examples and in the archives of this mailing list. The only difference in your case is that your custom driver would publish surround formats instead of stereo, thus fooling applications into thinking they had a surround output device. Meanwhile, inside your driver, you would down-mix those surround channels to stereo and pass them off to a real audio driver which only supports stereo. You really have no need for an AU in this scenario.
In other words, audio device drivers do not host AudioUnits. Only applications host AUs (and maybe some future device drivers).
You may be confused because the default audio output device AudioUnit provides the standard glue between an application and an audio output device, however, the audio driver is not hosting this AU - it's CoreAudio that is providing the link.
Brian Willoughby
Sound Consulting
On Feb 6, 2009, at 13:58, Ernest Burghardt wrote:
It seems like everything exists for what I would want to do, except that I would want have an AU that would install for a specific device and work for any application capable of playing audio, similar to a driver, but the requirement of an AU host application seems to complicate this idea.
I was hoping that an AU could take the place of doing the Mac version of a filter driver that would install over the device's audio class driver... I would love to wrong about this, so please feel free to correct my understanding.
In the case that I can not use a host-less AU, may I ask for recommendations for approaching this challenge?
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