Apple

On Sat, Aug 24, 2013 at 7:05 PM, Stefan Gretscher <email@hidden> wrote:

> I'm not sure you can accomplish what you want with an Audio Unit. It is my understanding that if the bus count is writable, a host can choose any number of busses -
> unless you're also implementing kAudioUnitProperty_SupportedNumChannels, which allows for limiting the total channel count across all busses, which may or may not be sufficient for your needs.

PS: another option that may fit your needs is to use a fixed bus count of 5, and then check which busses are actually connected when your Audio Unit is being initialized.

Be aware that both approaches allow for many more configurations than the ones you've listed below, including configurations that use both mono and stereo outputs at the same time.
Some hosts like AU Lab provide a nifty configuration UI, others like Logic try to pick a small sub-set which includes the typical use cases and present it as a menu. You'll have to experiment to get best results for your particular use case.

> Besides the documentation provided by Apple, you can search the archives of this list for more information, and study the implementation of CAAudioUnit::CanDo() in Apple's CoreAudio SDK.
> I've always felt expressing I/O capabilities is a weak spot of the Audio Unit specs and should be updated in some day. If you agree, file a bug.
>
> Best,
> Stefan
>
> Am 06.08.2013 um 11:28 schrieb Jan Weigel <email@hidden>:
>
>> Please, could anybody who has implemented an Audio Unit with a variable number of buses give me some information what is missing in the implementation I described below?
>> Thanks in advance.
>>
>> Cheers,
>> Jan
>>
>>
>> Am 05/08/2013 13:13, schrieb Jan Weigel:
>>> Hello,
>>>
>>> I have an Audio Unit Instrument that supports multiple output bus configurations.
>>> For example it supports:
>>> 1 stereo output bus,
>>> 2 stereo output buses
>>> 2 mono output buses
>>> 5 stereo output buses
>>> 5 mono output buses.
>>>
>>> I have implented BusCountWritable() to return true and SetBusCount() to return kAudioUnitErr_InvalidPropertyValue whenever inScope == kAudioUnitScope_Output and inCount is not a supported number.
>>>
>>> However in the Logic Plugin Menu it shows a lot of Output configurations that are not supported by the plugin:
>>> Mono
>>> Stereo
>>> Multi-Output (16x Mono)
>>> Multi-Output (1xStereo, 15xMono)
>>> Multi-Output (8xStereo, 8xMono)
>>> Multi-Output (16xStereo)
>>>
>>> What else do I have to implement to show only the supported configurations (the supported number of buses)?
>>> If I return false in BusCountWritable() then only the initial bus configuration is shown correctly but it is not possible to change the number of buses.
>>>
>>> Any help appreciated.
>>> Thanks
>>>
>>
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References:
	>Audio Unit: BusCountWritable Problem (From: Jan Weigel <email@hidden>)
	>Re: Audio Unit: BusCountWritable Problem (From: Jan Weigel <email@hidden>)
	>Re: Audio Unit: BusCountWritable Problem (From: Stefan Gretscher <email@hidden>)
	>Re: Audio Unit: BusCountWritable Problem (From: Stefan Gretscher <email@hidden>)
	>Re: Audio Unit: BusCountWritable Problem (From: Paul Davis <email@hidden>)