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Problems with first CoreAudio Example : (
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Problems with first CoreAudio Example : (


  • Subject: Problems with first CoreAudio Example : (
  • From: "sam aspin" <email@hidden>
  • Date: Mon, 31 Oct 2005 00:23:12 +0000

Hi, im a total mac/coreaudio noob and i'm having problems running the example code from the coreAudio SDK. I was simply hoping to play an audio file. I've tried a few of the different examples but here are the results from when i tried to build and run afplay

****************************************************
[Session started at 2005-10-31 00:15:00 +0000.]
Usage:
afplay [option...] audio_file

Options: (may appear before or after arguments)
 {-a --all}
   for files with >2 channels, play each pair of channels in succession
 {-f --frame} FRAME
   starting sample frame number
 {-s --seconds} START_SECONDS END_SECONDS
   segment of file to play, in seconds
error -35: open audio file

Error: open audio file (-35)
afplay has exited with status 1.
*****************************************************************

its saying theres an error opening the file but i havent specified a file for it to open???

i realise i maybe trying to use afplay in the wrong way but i've had similar probs with other examples

i did some googling on the error code and found it meant 'no such volume'...... some further googling suggested i may have errors on my HD so i ran the disk utility and found some errors which were repaired and followed by repairing the permissions.

any help would be greatly appreciated

Sam

From: email@hidden
Reply-To: email@hidden
To: email@hidden
Subject: Coreaudio-api Digest, Vol 2, Issue 332
Date: Sun, 30 Oct 2005 12:04:59 -0800 (PST)

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Today's Topics:

   1. Re: Channels and frames (john smith)
   2. Output AU buffer size for RenderCallback (Tim Dorcey)


----------------------------------------------------------------------

Message: 1
Date: Sun, 30 Oct 2005 08:03:05 +0100
From: "john smith" <email@hidden>
Subject: Re: Channels and frames
To: email@hidden
Cc: email@hidden
Message-ID: <email@hidden>
Content-Type: text/plain; format=flowed


Stefan,

Thanks for your help. This AU manager definitely sounds like what I need.
However, I'm unable to locate it.

I assume it is something that was installed with Logic? (FWIW, I'm running
LA7).


Thanks,

Michael Olsen

>From: Stefan Gretscher <email@hidden>
>To: john smith <email@hidden>
>CC: coreaudio-api Audio <email@hidden>
>Subject: Re: Channels and frames
>Date: Fri, 28 Oct 2005 15:31:02 +0200
>
>Am 28.10.2005 um 12:34 schrieb john smith:
>>I must have misunderstood something, because when using the following
>>code, the plug-in still shows up as mono->mono and mono->stereo in Logic.
>Logic caches the I/O capabilities of your AU - increase the version number
>of your AU or rescan the AU in the AU Manager to have Logic update its
>cache.
>Alternativley, use a version number of 0 during debug, this will cause
>Logic to always rescan your AU when it launches.
>
>Let me know if this doesn't fix your problem.
>
>Best,
>Stefan
>
>------------------------------------
>Stefan Gretscher
>
>plug-in development & 3rd party plug-in support
>Emagic GmbH, Hamburg, Germany
>a subsidiary of Apple Computer, Inc.
>
>email: email@hidden
>phone: (+49)-4101-495-586
>(Central European Timezone)
>


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------------------------------

Message: 2
Date: Sun, 30 Oct 2005 11:03:42 -0800
From: "Tim Dorcey" <email@hidden>
Subject: Output AU buffer size for RenderCallback
To: <email@hidden>
Message-ID: <002901c5dd84$a5f3d850$email@hidden>
Content-Type: text/plain; charset=iso-8859-1

I found mention in archives here that the value of "inNumberFrames" passed
to a RenderCallback for default Output Unit is determined by the attached
device's "I/O proc frame count."  Is this a property that clients can (or
should) change?

On my system, talking to "Built-in Audio," it seems to want about 12 msec
per render callback.  This is fine, and anything in the range < 100 msec
would be fine for my app.  Do I need to concern myself with getting
something outside that range, and how do I change it if so?

Also, I based my code on a "Quick and Dirty" example that was posted here,
which was nothing other than:
FindNextComponent()	kAudioUnitSubType_DefaultOutput
OpenAComponent()
AudioUnitSetProperty()	kAudioUnitProperty_StreamFormat
AudioUnitSetProperty()	kAudioUnitProperty_SetRenderCallback
AudioUnitInitialize()
AudioUnitStart()
...
AudioUnitStop()
AudioUnitUninitialize()
CloseComponent()

Then, my render callback simply fills the AudioBufferList presented to it.
Is that all there is to it?

Also, is it correct to presume that if I Open/Start multiple instances of
the Output AU, the audio streams will be mixed at final output?  And, each
could have a different stream format (e.g., sampling rate)?

Thanks,
Tim



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