Class WindowsAudioIo

This class uses the Windows Wave API to capture audio from a microphone and to send audio to the speakers or a headset. It is intended for use with Voice Over IP (VoIP) applications running under Windows.

Inheritance

object

WindowsAudioIo

Implements

IMMNotificationClient

IAudioSampleSource

Inherited Members

object.Equals(object)

object.Equals(object, object)

object.GetHashCode()

object.GetType()

object.MemberwiseClone()

object.ReferenceEquals(object, object)

object.ToString()

Namespace: SipLib.Audio.Windows

Assembly: SipLib.Audio.Windows.dll

Syntax

public class WindowsAudioIo : IMMNotificationClient, IAudioSampleSource

Constructors

WindowsAudioIo(int, string?)

Constructor

Declaration

public WindowsAudioIo(int SampleRate = 8000, string? DeviceName = null)

Parameters

Type	Name	Description
int	SampleRate	Sample rate in samples per second. Must be either 8000 or 16000. The default is 8000.
string	DeviceName	Specifies the audio device name as known by the Windows Wave API subsystem. The default is null. If null, then this class will pick the first available audio device.

Properties

SampleRate

Gets the configured sample rate in samples/second.

Declaration

public int SampleRate { get; }

Property Value

Type	Description
int

Methods

AudioOutSamplesReady(short[])

Sends the received PCM samples to the output device (speakers or headset).

Declaration

public void AudioOutSamplesReady(short[] PcmSamples)

Parameters

Type	Name	Description
short[]	PcmSamples	Received PCM samples (16-bit linear, 8000 or 16000 samples per second.

GetAudioDeviceNames()

Gets a list of available Wave API audio devices.

Declaration

public static List<string> GetAudioDeviceNames()

Returns

Type	Description
List<string>	Returns a list of device names. The list will be empty if there are no audio devices available.

OnDefaultDeviceChanged(DataFlow, Role, string)

IMMNotificationClient interface method. Called by the Windows multi-media subsystem when the default audio device has changed. The user of this WindowsAudioIo object should never call this method.

Declaration

public void OnDefaultDeviceChanged(DataFlow flow, Role role, string defaultDeviceId)

Parameters

Type	Name	Description
DataFlow	flow
Role	role
string	defaultDeviceId

OnDeviceAdded(string)

IMMNotificationClient interface method. Called by the Windows multi-media subsystem when an audio device has been added to the system. The user of this WindowsAudioIo object should never call this method.

Declaration

public void OnDeviceAdded(string pwstrDeviceId)

Parameters

Type	Name	Description
string	pwstrDeviceId

OnDeviceRemoved(string)

IMMNotificationClient interface method. Called by the Windows multi-media subsystem when an audio device has been removed from the system. The user of this WindowsAudioIo object should never call this method.

Declaration

public void OnDeviceRemoved(string deviceId)

Parameters

Type	Name	Description
string	deviceId

OnDeviceStateChanged(string, DeviceState)

IMMNotificationClient interface method. Called by the Windows multi-media subsystem when the audio device state changes. The user of this WindowsAudioIo object should never call this method.

Declaration

public void OnDeviceStateChanged(string deviceId, DeviceState newState)

Parameters

Type	Name	Description
string	deviceId
DeviceState	newState

OnPropertyValueChanged(string, PropertyKey)

IMMNotificationClient interface method. Called by the Windows multi-media subsystem when a property of an audio device has changed. The user of this WindowsAudioIo object should never call this method.

Declaration

public void OnPropertyValueChanged(string pwstrDeviceId, PropertyKey key)

Parameters

Type	Name	Description
string	pwstrDeviceId
PropertyKey	key

Start()

Tells the audio sample source to start sending audio samples by firing the SendAudioSamples event.

Declaration

public void Start()

StartAudio()

Sets up audio acquisition from the microphone and gets ready to start sending audio to the speakers or headset.

Declaration

public WaveAudioStatusEnum StartAudio()

Returns

Type	Description
WaveAudioStatusEnum	Returns Success if no errors were detected or an error code. Audio is not started if an error code is returned.

Stop()

Tells the audio sample source to stop sending audio samples.

Declaration

public void Stop()

StopAudio()

Call this method to stop the audio and gracefully shutdown.

Declaration

public void StopAudio()

Events

AudioDeviceStateChanged

This event is fired when the state of the Windows audio I/O device changes state.

Declaration

public event AudioDeviceStateChangedDelegate? AudioDeviceStateChanged

Event Type

Type	Description
AudioDeviceStateChangedDelegate

AudioSamplesReady

This event is fired when a full block of 20 milliseconds of audio data has been received from the microphone. Each sample point is a PCM sample (16-bit linear, 8000 or 16000 samples/second).

Declaration

public event AudioSamplesReadyDelegate? AudioSamplesReady

Event Type

Type	Description
AudioSamplesReadyDelegate

Implements

NAudio.CoreAudioApi.Interfaces.IMMNotificationClient

SipLib.Media.IAudioSampleSource