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# start(at:flags:IOProcID:)

Starts IO for the given AudioDeviceIOProcID and aligns the IO cycle of the device with the given time.

```
func start(at time: AudioTimeStamp, flags: UInt32 = 0, IOProcID: AudioDeviceIOProcID? = nil) throws -> AudioTimeStamp?
```

## Parameters

`time`

An AudioTimeStamp that containing the requested time to start the IOProc.

`flags`

A UInt32 containing flags that modify how this function behaves.

`IOProcID`

The AudioDeviceIOProcID to start. Note that this can be nil, which starts
the hardware regardless of whether or not there are any IOProcs registered.

## Return Value

An AudioTimeStamp containing the actual time the IOProc will start if the call
is successful.

## Discussion

An AudioHardwareError of kAudioHardwareUnsupportedOperationError will be thrown if the
device does not support starting at a specific time.
IOProcs should be written in C to ensure realtime safety.
IOProcIDs can be registered on the device with AudioDeviceCreateIOProcID or
AudioDeviceCreateIOProcIDWithBlock from AudioHardware.h.

---

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