/// <summary>
/// Constructs an <see cref="AudioConfig"/> from <see cref="Config"/>.
/// Depending on the available services, this may either use the audio features built into the Speech SDK (such as <see cref="AudioConfig.FromDefaultMicrophoneInput"/>),
/// or it may construct a <see cref="IStreamAudioSource"/> that accesses the requested <see cref="AudioDevice"/> with resampling and noise gates as required.
/// </summary>
/// <returns></returns>
protected AudioConfig GetAudioConfig()
{
var streamSource = GetStreamAudioSource(Config.AudioSource);
if (streamSource != null)
{
//use this stream source and convert to an Azure audio stream
try
{
var azureInput = AudioInputStream.CreatePushStream(AudioStreamFormat.GetWaveFormatPCM(
(uint)streamSource.Format.SampleRate,
(byte)streamSource.Format.BitsPerSample,
(byte)streamSource.Format.ChannelCount));
byte[] bufferOptional = null;
streamSource.DataAvailable += (s, e) =>
{
azureInput.Write(e.Buffer.GetArray(ref bufferOptional), e.Buffer.Count);
};
streamSource.Stopped += (s, e) =>
{
if (e.Cause == StreamAudioSourceStoppedCause.Stopped)
{
//signal end-of-stream to Azure
azureInput.Close();
}
};
this.StreamAudioSource = streamSource;
return(AudioConfig.FromStreamInput(azureInput));
}
catch (Exception ex)
{
Logger.LogError(ex, $"Error while creating an Azure AudioConfig from an IStreamAudioSource. Format: SampleRate={streamSource.Format.SampleRate}, BitsPerSample={streamSource.Format.BitsPerSample}, Channels={streamSource.Format.ChannelCount}");
streamSource.Dispose();
}
}
this.StreamAudioSource = null;
this.StreamAudioNoiseGate = null;
//try and use the built-in audio engine
if (Config.AudioSource is AudioDevice audioDevice)
{
if (audioDevice.UseDefaultAudioInputDevice)
{
return(AudioConfig.FromDefaultMicrophoneInput());
}
}
return(null);
}
/// <summary>
/// See <see cref="GetAudioConfig"/>: constructs a <see cref="IStreamAudioSource"/> for the given audio source (usually an <see cref="AudioDevice"/>).
/// Returns null if no <see cref="IStreamAudioSource"/> can be constructed from this source.
/// </summary>
/// <param name="configSource"></param>
/// <returns></returns>
protected IStreamAudioSource GetStreamAudioSource(IAudioSource configSource)
{
IStreamAudioSource streamSource = configSource as IStreamAudioSource;
if (streamSource != null)
{
//take care to keep the original stream intact
streamSource = new NonDisposingStreamAudioSource(streamSource);
}
else
{
//read from blob/device
var provider = ServiceProvider.GetService(typeof(IStreamAudioSourceProvider)) as IStreamAudioSourceProvider;
streamSource = provider?.GetStreamAudioSource(configSource);
}
if (streamSource == null)
{
Logger.LogError($"Cannot read from AudioDevice: could not construct an IStreamAudioSource");
return(null);
}
//add a noisegate to avoid unnecessary costs when there's no actual sound. probably best to do that before resampling => saves some processing power
var noiseGateProvider = ServiceProvider.GetService(typeof(INoiseGateStreamAudioProcessProvider)) as INoiseGateStreamAudioProcessProvider;
var noiseGate = noiseGateProvider?.GetNoiseGate(streamSource);
if (noiseGate != null)
{
noiseGate.SetOptions(new NoiseGateStreamAudioProcessorOptions()
{
VolumeThreshold = Config.VolumeThreshold,
Delay = TimeSpan.FromSeconds(5),
DelayStopDetection = TimeSpan.FromSeconds(2)
});
streamSource = noiseGate;
StreamAudioNoiseGate = noiseGate;
}
else
{
Logger.LogWarning($"No noisegate available. Input format: {streamSource.Format}");
}
//check on the wave format
//according to https://docs.microsoft.com/en-us/azure/cognitive-services/speech-service/audio-processing-overview#minimum-requirements-to-use-microsoft-audio-stack
//-we need multiples of 16kHz
//-"32-bit IEEE little endian float, 32-bit little endian signed int, 24-bit little endian signed int, 16-bit little endian signed int, or 8-bit signed int"
//--(though the API doesn't seem to allow float formats)
//additionally: more than one channel increases the API cost
var sourceFormat = streamSource.Format;
bool resampleRequired = sourceFormat.SampleRate % 16000 != 0 ||
!sourceFormat.IntEncoded ||
!sourceFormat.IntEncodingSigned ||
!sourceFormat.ByteOrderLittleEndian ||
sourceFormat.ChannelCount > 1;
if (resampleRequired)
{
//get a resampler
WaveStreamAudioFormat targetFormat = WaveStreamAudioFormat.GetIntFormat(
sampleRate: sourceFormat.SampleRate / 16000 * 16000,
bitsPerSample: Math.Min(sourceFormat.BitsPerSample / 8 * 8, 32),
channelCount: 1,
signed: true,
littleEndian: true
);
var provider = ServiceProvider.GetService(typeof(IStreamAudioResamplerProvider)) as IStreamAudioResamplerProvider;
var resampler = provider?.GetResampler(streamSource, targetFormat);
if (resampler != null)
{
streamSource = resampler;
}
else
{
//can't resample
Logger.LogError($"No resampler available. Input format: {sourceFormat}");
streamSource.Dispose();
return(null);
}
}
return(streamSource);
}
