A Simple and Efficient Audio Resampler Implementation in C.
uint64_t Resample_f32(const float *input, float *output, int inSampleRate, int outSampleRate, uint64_t inputSize,
uint32_t channels) {
if (input == NULL)
return 0;
uint64_t outputSize = (uint64_t) (inputSize * (double) outSampleRate / (double) inSampleRate);
outputSize -= outputSize % channels;
if (output == NULL)
return outputSize;
double stepDist = ((double) inSampleRate / (double) outSampleRate);
const uint64_t fixedFraction = (1LL << 32);
const double normFixed = (1.0 / (1LL << 32));
uint64_t step = ((uint64_t) (stepDist * fixedFraction + 0.5));
uint64_t curOffset = 0;
for (uint32_t i = 0; i < outputSize - channels; i += channels) {
uint64_t currentPos = curOffset >> 32;
uint64_t nextPos = currentPos + 1;
for (uint32_t c = 0; c < channels; c++) {
float current = input[currentPos * channels + c];
float next = input[nextPos * channels + c];
double frac = (curOffset & (fixedFraction - 1)) * normFixed;
*output++ = (float) (current + (next - current) * frac);
}
curOffset += step;
uint64_t frameSkip = (curOffset >> 32);
curOffset &= (fixedFraction - 1);
input += frameSkip * channels;
}
uint64_t lastPos = (curOffset >> 32);
for (uint32_t c = 0; c < channels; c++) {
*output++ = input[lastPos * channels + c];
}
return outputSize;
}
uint64_t Resample_s16(const int16_t *input, int16_t *output, int inSampleRate, int outSampleRate, uint64_t inputSize,
uint32_t channels) {
if (input == NULL)
return 0;
uint64_t outputSize = (uint64_t) (inputSize * (double) outSampleRate / (double) inSampleRate);
outputSize -= outputSize % channels;
if (output == NULL)
return outputSize;
double stepDist = ((double) inSampleRate / (double) outSampleRate);
const uint64_t fixedFraction = (1LL << 32);
const double normFixed = (1.0 / (1LL << 32));
uint64_t step = ((uint64_t) (stepDist * fixedFraction + 0.5));
uint64_t curOffset = 0;
for (uint32_t i = 0; i < outputSize - channels; i += channels) {
uint64_t currentPos = curOffset >> 32;
uint64_t nextPos = currentPos + 1;
for (uint32_t c = 0; c < channels; c++) {
int16_t current = input[currentPos * channels + c];
int16_t next = input[nextPos * channels + c];
double frac = (curOffset & (fixedFraction - 1)) * normFixed;
*output++ = (int16_t) (current + (next - current) * frac);
}
curOffset += step;
uint64_t frameSkip = (curOffset >> 32);
curOffset &= (fixedFraction - 1);
input += frameSkip * channels;
}
uint64_t lastPos = (curOffset >> 32);
for (uint32_t c = 0; c < channels; c++) {
*output++ = input[lastPos * channels + c];
}
return outputSize;
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