Expresses valid combinations of input and output channels.
- iOS 10.0+
- macOS 10.12+
- Mac Catalyst 13.0+
- tvOS 10.0+
Array elements are
NSNumber values containing integers.
The array index alternates between input and output counts, in ascending order of input/output channels—for example:  = first input count,  = first output count,  = second input count,  = second output count, etc.
Positive array values specify the number of input and/or output channels supported.
Negative array values have particular meanings. An input/output value pair of
(-1, -1) (i.e.  = -1,  = -1) indicates that any number of channels are supported, as long as they are the same number for both input and output. An input/output value pair combination of
-2 (e.g.  = -1,  = -2) also indicates that any number of channels are supported, but without the requirement that the input and output counts are the same. A negative value less than
-2 (e.g.  = -16) specifies a total number of channels across every bus in that scope, regardless of how many channels are set on any particular bus.
An array value of
0 (e.g.  = 0) specifies that the input/output channel is not applicable (though typically only used for input channels).
Table 1 shows a sample selection of valid input and output channel combinations:
First input/output count.
Any number of input and output channels, requiring that the numbers match. This is the default case.
Second input/output count.
Any number of input and output channels, without requiring that the numbers match.
Third input/output count.
Exactly two input channels, exactly six output channels.
Fourth input/output count.
Any number of input channels, exactly two output channels.
Fifth input/output count.
No input channels, exactly one output channel.
Sixth input/output count.
Up to four input channels, up to eight output channels.
This version 3 property is bridged to the version 2 kAudioUnitProperty_SupportedNumChannels API.