/// <summary>
/// Creates a new audio format based on a well known codec.
/// </summary>
public AudioFormat(
AudioCodecsEnum codec,
int formatID,
int clockRate = DEFAULT_CLOCK_RATE,
int channelCount = DEFAULT_CHANNEL_COUNT,
string parameters = null) :
this(codec, formatID, clockRate, clockRate, channelCount, parameters)
{
}
/// <summary>
/// Creates a new audio format based on a well known codec.
/// </summary>
public AudioFormat(
AudioCodecsEnum codec,
int formatID,
int clockRate,
int rtpClockRate,
int channelCount,
string parameters)
: this(formatID, codec.ToString(), clockRate, rtpClockRate, channelCount, parameters)
{
}
public byte[] EncodeAudio(byte[] pcm, AudioCodecsEnum codec, AudioSamplingRatesEnum sampleRate)
{
// Convert buffer into a PCM sample (array of signed shorts) that's
// suitable for input into the chosen encoder.
short[] pcmSigned = new short[pcm.Length / 2];
for (int i = 0; i < pcmSigned.Length; i++)
{
pcmSigned[i] = BitConverter.ToInt16(pcm, i * 2);
}
return(EncodeAudio(pcmSigned, codec, sampleRate));
}
public bool IsSupported(AudioCodecsEnum codec)
{
switch (codec)
{
case AudioCodecsEnum.G722:
case AudioCodecsEnum.PCMA:
case AudioCodecsEnum.PCMU:
return(true);
default:
return(false);
}
}
/// <summary>
/// Attempts to get the RTP clock rate of known payload types. Generally this will be the same
/// as the clock rate but in some cases for seemingly historical reasons they are different
/// </summary>
/// <param name="mediaType">The media type to get the clock rate for.</param>
/// <returns>An integer representing the payload type's RTP timestamp frequency or 0
/// if it's not known.</returns>
public static int GetRtpDefaultClockRate(AudioCodecsEnum codec)
{
switch (codec)
{
case AudioCodecsEnum.PCMA:
case AudioCodecsEnum.PCMU:
case AudioCodecsEnum.G722:
return(8000);
case AudioCodecsEnum.OPUS:
return(48000);
default:
return(8000);
}
}
public void SetAudioSourceFormat(AudioCodecsEnum audioFormat)
{
_sendingFormat = audioFormat;
}
public void SetAudioSinkFormat(AudioCodecsEnum audioFormat)
{
_selectedSinkFormat = audioFormat;
}
public void SetAudioSourceFormat(AudioCodecsEnum audioFormat)
{
_selectedSourceFormat = audioFormat;
_externalSource?.SetAudioSourceFormat(audioFormat);
}
public byte[] EncodeAudio(short[] pcm, AudioCodecsEnum codec, AudioSamplingRatesEnum sampleRate)
{
byte[] encodedSample = null;
if (codec == AudioCodecsEnum.G722)
{
if (_g722Codec == null)
{
_g722Codec = new G722Codec();
_g722CodecState = new G722CodecState(G722_BIT_RATE, G722Flags.None);
}
if (sampleRate == AudioSamplingRatesEnum.Rate16KHz)
{
// No up sampling required.
int outputBufferSize = pcm.Length / 2;
encodedSample = new byte[outputBufferSize];
int res = _g722Codec.Encode(_g722CodecState, encodedSample, pcm, pcm.Length);
}
else
{
// Up sample the supplied PCM signal by doubling each sample.
int outputBufferSize = pcm.Length;
encodedSample = new byte[outputBufferSize];
short[] pcmUpsampled = new short[pcm.Length * 2];
for (int i = 0; i < pcm.Length; i++)
{
pcmUpsampled[i * 2] = pcm[i];
pcmUpsampled[i * 2 + 1] = pcm[i];
}
_g722Codec.Encode(_g722CodecState, encodedSample, pcmUpsampled, pcmUpsampled.Length);
}
return(encodedSample);
}
else if (codec == AudioCodecsEnum.PCMA ||
codec == AudioCodecsEnum.PCMU)
{
Func <short, byte> encode = (codec == AudioCodecsEnum.PCMA) ?
(Func <short, byte>)ALawEncoder.LinearToALawSample : MuLawEncoder.LinearToMuLawSample;
if (sampleRate == AudioSamplingRatesEnum.Rate8KHz)
{
// No down sampling required.
int outputBufferSize = pcm.Length;
encodedSample = new byte[outputBufferSize];
for (int index = 0; index < pcm.Length; index++)
{
encodedSample[index] = encode(pcm[index]);
}
}
else
{
// Down sample the supplied PCM signal by skipping every second sample.
int outputBufferSize = pcm.Length / 2;
encodedSample = new byte[outputBufferSize];
int encodedIndex = 0;
// Skip every second sample.
for (int index = 0; index < pcm.Length; index += 2)
{
encodedSample[encodedIndex++] = encode(pcm[index]);
}
}
return(encodedSample);
}
else
{
throw new ApplicationException($"Audio format {codec} cannot be encoded.");
}
}
/// <summary>
/// Event handler for receiving RTP packets from the remote party.
/// </summary>
/// <param name="remoteEP">The remote end point the RTP was received from.</param>
/// <param name="codec">The encoding codec of the packets.</param>
/// <param name="rtpPacket">The RTP packet with the media sample.</param>
public byte[] DecodeAudio(byte[] encodedSample, AudioCodecsEnum codec, AudioSamplingRatesEnum sampleRate)
{
bool wants8kSamples = sampleRate == AudioSamplingRatesEnum.Rate8KHz;
bool wants16kSamples = sampleRate == AudioSamplingRatesEnum.Rate16KHz;
if (codec == AudioCodecsEnum.G722)
{
if (_g722Decoder == null)
{
_g722Decoder = new G722Codec();
_g722DecoderState = new G722CodecState(G722_BIT_RATE, G722Flags.None);
}
short[] decodedPcm16k = new short[encodedSample.Length * 2];
int decodedSampleCount = _g722Decoder.Decode(_g722DecoderState, decodedPcm16k, encodedSample, encodedSample.Length);
// The decoder provides short samples but streams and devices generally seem to want
// byte samples so convert them.
byte[] pcm8kBuffer = (wants8kSamples) ? new byte[decodedSampleCount] : null;
byte[] pcm16kBuffer = (wants16kSamples) ? new byte[decodedSampleCount * 2] : null;
for (int i = 0; i < decodedSampleCount; i++)
{
var bufferSample = BitConverter.GetBytes(decodedPcm16k[i]);
// For 8K samples the crude re-sampling to get from 16K to 8K is to skip
// every second sample.
if (pcm8kBuffer != null && i % 2 == 0)
{
pcm8kBuffer[(i / 2) * 2] = bufferSample[0];
pcm8kBuffer[(i / 2) * 2 + 1] = bufferSample[1];
}
// G722 provides 16k samples.
if (pcm16kBuffer != null)
{
pcm16kBuffer[i * 2] = bufferSample[0];
pcm16kBuffer[i * 2 + 1] = bufferSample[1];
}
}
return(pcm8kBuffer ?? pcm16kBuffer);
}
else if (codec == AudioCodecsEnum.PCMA ||
codec == AudioCodecsEnum.PCMU)
{
Func <byte, short> decode = (codec == AudioCodecsEnum.PCMA) ?
(Func <byte, short>)ALawDecoder.ALawToLinearSample : MuLawDecoder.MuLawToLinearSample;
byte[] pcm8kBuffer = (wants8kSamples) ? new byte[encodedSample.Length * 2] : null;
byte[] pcm16kBuffer = (wants16kSamples) ? new byte[encodedSample.Length * 4] : null;
for (int i = 0; i < encodedSample.Length; i++)
{
var bufferSample = BitConverter.GetBytes(decode(encodedSample[i]));
// G711 samples at 8KHz.
if (pcm8kBuffer != null)
{
pcm8kBuffer[i * 2] = bufferSample[0];
pcm8kBuffer[i * 2 + 1] = bufferSample[1];
}
// The crude up-sampling approach to get 16K samples from G711 is to
// duplicate each 8K sample.
// TODO: This re-sampling approach introduces artifacts. Applying a low pass
// filter seems to be recommended.
if (pcm16kBuffer != null)
{
pcm16kBuffer[i * 4] = bufferSample[0];
pcm16kBuffer[i * 4 + 1] = bufferSample[1];
pcm16kBuffer[i * 4 + 2] = bufferSample[0];
pcm16kBuffer[i * 4 + 3] = bufferSample[1];
}
}
return(pcm8kBuffer ?? pcm16kBuffer);
}
else
{
throw new ApplicationException($"Audio format {codec} cannot be decoded.");
}
}
