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Re: what would cause QTSetComponentProperty to fail with a kAudioUnitErr_InvalidPropertyValue err?
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Re: what would cause QTSetComponentProperty to fail with a kAudioUnitErr_InvalidPropertyValue err?


  • Subject: Re: what would cause QTSetComponentProperty to fail with a kAudioUnitErr_InvalidPropertyValue err?
  • From: Jeff Moore <email@hidden>
  • Date: Thu, 22 Mar 2007 08:50:19 -0700

That might be correct, but it still is not the proper way to implement the kind of audio driver Mr. Dautermann is describing. As I said in my previous email, this kind of driver needs to be written in a two parts. First, there needs to be a daemon that handles the actual interaction with the hardware. Then the HAL plug-in and the vdig component communicate with the daemon using shared memory and the IPC API of your choice (I prefer Mach IPC using MIG).

The real practical outcome of trying to do it the way Mr. Dautermann is describing is the multitude of bugs with applications that try to use the device expecting it to work like every other device and the incredible hate from users that the iSight driver and Digidesign's first attempt at integrating the DAE into the HAL engendered. It wasn't pretty and if memory serves, one of the primary APIs that had big problems with those drivers at the time was QuickTime's Sequence Grabber.

So the take away here is, take short cuts at your own peril!

On Mar 22, 2007, at 7:42 AM, Chandrasekhar Ramakrishnan wrote:


Am 20.03.2007 um 22:30 schrieb Michael Dautermann:

I'd love to be able to fully use HALLab for my validation tool, and the plug-in seems to do all the right things at least on the Info dialog (the main dialog) of HALLab.

In the big picture, audio data for the plug-in comes from a Quicktime 'vdig' component I've written that gathers video and audio streams from a USB device. Because this 'vdig' needs to be running, I don't think I can easily use HALLab play-through to do validation. I have to do it this way as a USB device can only be exclusively opened by one process / app at a time (and 'vdig' counts for one and 'audi' for another).

I have an AudioHardwarePlugIn that uses AudioUnits and thus the component manager internally. This works fine.


The one tricky aspect was instantiating the components at the right moment -- I couldn't do this in the Initialize() method because I was encountering problems with reentrancy and the ComponentManager when the app requesting the HAL plugin uses the AUHAL audio unit. Moving the component instantiation to a later point in time solves that.


--

Jeff Moore
Core Audio
Apple




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  • Follow-Ups:
    • Re: what would cause QTSetComponentProperty to fail with a kAudioUnitErr_InvalidPropertyValue err?
      • From: Michael Dautermann <email@hidden>
References: 
 >what would cause QTSetComponentProperty to fail with a kAudioUnitErr_InvalidPropertyValue err? (From: Michael Dautermann <email@hidden>)
 >Re: what would cause QTSetComponentProperty to fail with a kAudioUnitErr_InvalidPropertyValue err? (From: Brad Ford <email@hidden>)
 >Re: what would cause QTSetComponentProperty to fail with a kAudioUnitErr_InvalidPropertyValue err? (From: Michael Dautermann <email@hidden>)
 >Re: what would cause QTSetComponentProperty to fail with a kAudioUnitErr_InvalidPropertyValue err? (From: Jeff Moore <email@hidden>)
 >Re: what would cause QTSetComponentProperty to fail with a kAudioUnitErr_InvalidPropertyValue err? (From: Michael Dautermann <email@hidden>)
 >Re: what would cause QTSetComponentProperty to fail with a kAudioUnitErr_InvalidPropertyValue err? (From: Jeff Moore <email@hidden>)
 >Re: what would cause QTSetComponentProperty to fail with a kAudioUnitErr_InvalidPropertyValue err? (From: Michael Dautermann <email@hidden>)
 >Re: what would cause QTSetComponentProperty to fail with a kAudioUnitErr_InvalidPropertyValue err? (From: Jeff Moore <email@hidden>)
 >Re: what would cause QTSetComponentProperty to fail with a kAudioUnitErr_InvalidPropertyValue err? (From: Michael Dautermann <email@hidden>)
 >Re: what would cause QTSetComponentProperty to fail with a kAudioUnitErr_InvalidPropertyValue err? (From: Brad Ford <email@hidden>)
 >Re: what would cause QTSetComponentProperty to fail with a kAudioUnitErr_InvalidPropertyValue err? (From: Michael Dautermann <email@hidden>)
 >Re: what would cause QTSetComponentProperty to fail with a kAudioUnitErr_InvalidPropertyValue err? (From: Chandrasekhar Ramakrishnan <email@hidden>)

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