/// <summary>
/// Decodes an 8Khz array of 8-bit encoded values into an equivalent set of 16-bit samples
/// </summary>
/// <param name="encodedFrame">A short array with the encoded values</param>
/// <param name="inputStart">The starting position IN SHORTS of the samples</param>
/// <param name="inputLength">The length of the samples IN SHORTS</param>
/// <param name="decodedFrame">The output frame</param>
/// <param name="outputStart">The starting position IN SHORTS in the output buffer where the decoded data should be written</param>
/// <param name="isSilent">Whether the samples contain silence</param>
/// <returns>The length of the decoded samples IN SHORTS</returns>
public int Decode(short[] encodedFrame, int inputStart, int inputLength, short[] decodedFrame, int outputStart, bool isSilent)
{
if (isSilent)
{
Array.Clear(decodedFrame, outputStart, _outputAudioFormat.SamplesPerFrame);
return(_outputAudioFormat.SamplesPerFrame);
}
// Decode
int decodedPos = outputStart;
if (_outputAudioFormat.SamplesPerSecond == 16000)
{
for (int i = inputStart; i < inputStart + inputLength; i++)
{
byte b1;
byte b2;
G711.FromShort(encodedFrame[i], out b1, out b2);
decodedFrame[decodedPos] = G711.ULawToLinearFast(b1);
decodedPos += 2;
decodedFrame[decodedPos] = G711.ULawToLinearFast(b2);
decodedPos += 2;
}
// Upsample using linear interpolation. Not the best quality, but cheap on CPU.
for (int i = 1; i < decodedPos - 1; i += 2)
{
decodedFrame[i] = (short)((decodedFrame[i - 1] + decodedFrame[i + 1]) / 2);
}
decodedFrame[decodedPos - 1] = decodedFrame[decodedPos - 2]; // Cheat on the last sample
}
else
{
for (int i = inputStart; i < inputStart + inputLength; i++)
{
byte b1;
byte b2;
G711.FromShort(encodedFrame[i], out b1, out b2);
decodedFrame[decodedPos++] = G711.ULawToLinearFast(b1);
decodedFrame[decodedPos++] = G711.ULawToLinearFast(b2);
}
}
return(decodedPos - outputStart);
}
/// <summary>
/// Decodes an 8Khz array of 8-bit encoded values into an equivalent set of 16-bit samples (and upsamples them to 16Khz if necessary).
/// </summary>
/// <param name="encodedFrame">A byte array with the encoded values</param>
/// <param name="inputStart">The starting position IN BYTES of the samples</param>
/// <param name="inputLength">The length of the samples IN BYTES</param>
/// <param name="decodedFrame">The output frame</param>
/// <param name="outputStart">The starting position IN BYTES of the output buffer where the decoded data should be written.</param>
/// <param name="isSilent">Whether the samples contain silence</param>
/// <returns>The length of the decoded samples IN BYTES</returns>
public int Decode(byte[] encodedFrame, int inputStart, int inputLength, byte[] decodedFrame, int outputStart, bool isSilent)
{
if (isSilent)
{
Array.Clear(decodedFrame, outputStart, _outputAudioFormat.BytesPerFrame);
return(_outputAudioFormat.BytesPerFrame);
}
int end = inputStart + inputLength;
int decodedPos = outputStart;
if (_outputAudioFormat.SamplesPerSecond == 16000)
{
// Decode
for (int i = inputStart; i < end; i++)
{
short decodedSample = G711.ULawToLinearFast(encodedFrame[i]);
G711.FromShort(decodedSample, out decodedFrame[decodedPos++], out decodedFrame[decodedPos++]);
decodedPos += 2;
}
// Upsample
short next = 0;
for (int i = 2; i < decodedPos - 2; i += 4)
{
short previous = G711.ToShort(decodedFrame[i - 2], decodedFrame[i - 1]);
next = G711.ToShort(decodedFrame[i + 2], decodedFrame[i + 3]);
G711.FromShort((short)((previous + next) / 2), out decodedFrame[i], out decodedFrame[i + 1]);
}
G711.FromShort(next, out decodedFrame[decodedPos - 2], out decodedFrame[decodedPos - 1]); // Cheat on the last sample
}
else // if outputAudioFormat.SamplesPerSecond = 8000
{
// Decode
for (int i = inputStart; i < end; i++)
{
short decodedSample = G711.ULawToLinearFast(encodedFrame[i]);
G711.FromShort(decodedSample, out decodedFrame[decodedPos++], out decodedFrame[decodedPos++]);
}
}
return(decodedPos - outputStart);
}
