static int AdpcmImaWavExpandNibble(ref ImaState channel, int nibble)
{
int diff = stepTable[channel.stepIndex] >> 3;
if ((nibble & 0x04) != 0)
{
diff += stepTable[channel.stepIndex];
}
if ((nibble & 0x02) != 0)
{
diff += stepTable[channel.stepIndex] >> 1;
}
if ((nibble & 0x01) != 0)
{
diff += stepTable[channel.stepIndex] >> 2;
}
if ((nibble & 0x08) != 0)
{
channel.predictor -= diff;
}
else
{
channel.predictor += diff;
}
if (channel.predictor < -32768)
{
channel.predictor = -32768;
}
else if (channel.predictor > 32767)
{
channel.predictor = 32767;
}
channel.stepIndex += indexTable[nibble];
if (channel.stepIndex < 0)
{
channel.stepIndex = 0;
}
else if (channel.stepIndex > 88)
{
channel.stepIndex = 88;
}
return(channel.predictor);
}
// Convert buffer containing IMA/ADPCM wav data to a 16-bit signed PCM buffer
internal static byte[] ConvertIma4ToPcm(byte[] buffer, int offset, int count, int channels, int blockAlignment)
{
ImaState channel0 = new ImaState();
ImaState channel1 = new ImaState();
int sampleCountFullBlock = ((blockAlignment / channels) - 4) / 4 * 8 + 1;
int sampleCountLastBlock = 0;
if ((count % blockAlignment) > 0)
{
sampleCountLastBlock = (((count % blockAlignment) / channels) - 4) / 4 * 8 + 1;
}
int sampleCount = ((count / blockAlignment) * sampleCountFullBlock) + sampleCountLastBlock;
var samples = new byte[sampleCount * sizeof(short) * channels];
int sampleOffset = 0;
while (count > 0)
{
int blockSize = blockAlignment;
if (count < blockSize)
{
blockSize = count;
}
count -= blockAlignment;
channel0.predictor = buffer[offset++];
channel0.predictor |= buffer[offset++] << 8;
if ((channel0.predictor & 0x8000) != 0)
{
channel0.predictor -= 0x10000;
}
channel0.stepIndex = buffer[offset++];
if (channel0.stepIndex > 88)
{
channel0.stepIndex = 88;
}
offset++;
int index = sampleOffset * 2;
samples[index] = (byte)channel0.predictor;
samples[index + 1] = (byte)(channel0.predictor >> 8);
++sampleOffset;
if (channels == 2)
{
channel1.predictor = buffer[offset++];
channel1.predictor |= buffer[offset++] << 8;
if ((channel1.predictor & 0x8000) != 0)
{
channel1.predictor -= 0x10000;
}
channel1.stepIndex = buffer[offset++];
if (channel1.stepIndex > 88)
{
channel1.stepIndex = 88;
}
offset++;
index = sampleOffset * 2;
samples[index] = (byte)channel1.predictor;
samples[index + 1] = (byte)(channel1.predictor >> 8);
++sampleOffset;
}
if (channels == 2)
{
for (int nibbles = 2 * (blockSize - 8); nibbles > 0; nibbles -= 16)
{
for (int i = 0; i < 4; i++)
{
index = (sampleOffset + i * 4) * 2;
int sample = AdpcmImaWavExpandNibble(ref channel0, buffer[offset + i] & 0x0f);
samples[index] = (byte)sample;
samples[index + 1] = (byte)(sample >> 8);
index = (sampleOffset + i * 4 + 2) * 2;
sample = AdpcmImaWavExpandNibble(ref channel0, buffer[offset + i] >> 4);
samples[index] = (byte)sample;
samples[index + 1] = (byte)(sample >> 8);
}
offset += 4;
for (int i = 0; i < 4; i++)
{
index = (sampleOffset + i * 4 + 1) * 2;
int sample = AdpcmImaWavExpandNibble(ref channel1, buffer[offset + i] & 0x0f);
samples[index] = (byte)sample;
samples[index + 1] = (byte)(sample >> 8);
index = (sampleOffset + i * 4 + 3) * 2;
sample = AdpcmImaWavExpandNibble(ref channel1, buffer[offset + i] >> 4);
samples[index] = (byte)sample;
samples[index + 1] = (byte)(sample >> 8);
}
offset += 4;
sampleOffset += 16;
}
}
else
{
for (int nibbles = 2 * (blockSize - 4); nibbles > 0; nibbles -= 2)
{
index = (sampleOffset * 2);
int b = buffer[offset];
int sample = AdpcmImaWavExpandNibble(ref channel0, b & 0x0f);
samples[index] = (byte)sample;
samples[index + 1] = (byte)(sample >> 8);
index += 2;
sample = AdpcmImaWavExpandNibble(ref channel0, b >> 4);
samples[index] = (byte)sample;
samples[index + 1] = (byte)(sample >> 8);
sampleOffset += 2;
++offset;
}
}
}
return(samples);
}
