Re: HAL Devices and Streams
Re: HAL Devices and Streams
- Subject: Re: HAL Devices and Streams
- From: <email@hidden>
- Date: Sun, 13 Jan 2002 20:06:51 -0600
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on 1/11/02 2:44 PM, email@hidden <email@hidden> wrote:
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> I've noticed on OS X (up to 10.1.2 at least) QuickTime doesn't seem to have
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> the same access to multiple audio devices as OS 9, namely USB audio.
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>
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> The list of available audio devices QuickTime API's FindNextComponent and
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> GetComponentInfo functions give is limited to FireWire DV, and two
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> variations of "HAL System". In contrast, under OS 9 with a USB audio device
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> connected (Griffin iMic), QuickTime has access to both "Built-In" and "USB
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> Audio", as it should.
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>
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> Is this a limitation of the current QuickTime on OS X, or CoreAudio? What
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> will be done about this limitation in the future?
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>
The Sound Manager provides an sdev component to talk to the HAL. It is the
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default component. This component by default talks to whatever the HAL
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thinks of as the default device. This provides pretty much the expected
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behavior.
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Since the Sound Manager is shimmed on top of the HAL and doesn't provide an
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API that abstracts out the device discovery process (like the Sound Input
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Manager does),
Jeff, thanks for the reply. I'm a little worried... Are there no plans to
make QuickTime's multiple soundcard support function on OS X as it does on
OS 9? Since "FireWire DV" is listed as an output option, I would hope USB
audio, and any other connected audio devices would also be supported in the
future. We need QuickTime to be able to play different audio tracks on
multiple sound outputs... namely 'Built-In' and/or USB audio, or VXPocket,
etc, and use them simultaneously.
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it isn't feasible to provide a component for every device the
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HAL knows about since they can come and go pretty much at will.
Audio devices come and go at will under OS 9 too. USB audio for example...
The QuickTime API under OS 9 did not have a problem with this. Why not
bridge the QuickTime component API calls to work with any discovered HAL
output devices?
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Therefore, it has just the one sdev component, but this component provides a
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mechanism to tell this it what HAL device to use (the siHALAudioDeviceID
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Get/SetInfo constant).
...but only for one device at a time, for all QuickTime playback, right?
Will QuickTime eventually bypass the SoundManager in future versions?
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Given how the Sound Manager works, it really isn't going to be possible to
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make it work the way you would like on X.
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--
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Jeff Moore
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Core Audio
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Apple
My application development is moving to X, and it uses QuickTime with
multiple outputs. I hope Apple seriously looks into supporting this on X,
and the QuickTime and CoreAudio teams work together to solve any problems.
Thanks again,
Jason