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Add .outputSeek() for playing back samples

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Geraint 2025-08-10 20:13:54 +01:00
parent 12de19e05d
commit c3fcda8563
2 changed files with 99 additions and 22 deletions
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34
cmd/main.cpp
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@ -51,18 +51,36 @@ int main(int argc, char* argv[]) {
stretch.exact(inWav, int(inputLength), outWav, int(outputLength));
However, we'll do it in separate stages to demonstrate more of the API.
*/
However, we'll do it in separate stages to show more of the API. */
// First, an "output seek"
// This is suitable for starting playback of a sample at a given playback rate:
auto seekSamples = stretch.outputSeekSamples(1/time);
stretch.outputSeek(inWav, seekSamples);
// At this point, the next output samples we get will correspond to the beginning of the audio file
// First, an "output seek", where we provide a chunk of input.
// This is suitable for starting playback of a sample at a given playback rate.
auto seekLength = stretch.outputSeekLength(1/time);
stretch.outputSeek(inWav, seekLength);
// At this point, the next output samples we get will correspond to the beginning of the audio file.
// We're going to process until *just* before the end of the audio file (so we can get a tidier end using `.flush()`.
int outputIndex = outputLength - stretch.outputLatency();
// Stretch's internal output position is slightly ahead of the output samples we get
int outputPos = outputLength + stretch.outputLatency();
// Time-map: where do we want the input position to be at that moment?
int inputPos = std::round(outputPos/time);
// And therefore which input samples do we need to be supplying?
int inputIndex = inputPos + stretch.inputLatency();
stretch.exact(inWav, int(inputLength), outWav, int(outputLength));
// In this particular case, our `inputPos` will be at the end of the file
// and `inputIndex` will be beyond the end, so we pad with 0s to have enough input
inWav.resize(inputIndex);
// OK, go for it
inWav.offset = seekLength;
stretch.process(inWav, inputIndex - seekLength, outWav, outputIndex);
// And as promised, get the last bits using `.flush()`, which does some extra stuff to avoid introducing clicks.
outWav.offset = outputIndex;
stretch.flush(outWav, outputLength - outputIndex);
outWav.offset = 0;
if (!outWav.write(outputWav).warn()) args.errorExit("failed to write WAV");
}

79
signalsmith-stretch.h
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@ -38,12 +38,7 @@ struct SignalsmithStretch {
SignalsmithStretch() : randomEngine(std::random_device{}()) {}
SignalsmithStretch(long seed) : randomEngine(seed) {}
int blockSamples() const {
return int(stft.blockSamples());
}
int intervalSamples() const {
return int(stft.defaultInterval());
}
// The difference between the internal position (centre of a block) and the input samples you're supplying
int inputLatency() const {
return int(stft.analysisLatency());
}
@ -81,7 +76,6 @@ struct SignalsmithStretch {
stft.reset(0.1);
stashedInput = stft.input;
stashedOutput = stft.output;
tmpBuffer.resize(blockSamples + intervalSamples);
bands = int(stft.bands());
channelBands.assign(bands*channels, Band());
@ -94,6 +88,18 @@ struct SignalsmithStretch {
blockProcess = {};
formantMetric.resize(bands + 2);
tmpBuffer.resize(std::max(outputLatency()*channels, blockSamples + intervalSamples));
}
// For querying the existing config
int blockSamples() const {
return int(stft.blockSamples());
}
int intervalSamples() const {
return int(stft.defaultInterval());
}
bool splitComputation() const {
return _splitComputation;
}
/// Frequency multiplier, and optional tonality limit (as multiple of sample-rate)
@ -127,7 +133,8 @@ struct SignalsmithStretch {
formantBaseFreq = baseFreq;
}
// Provide previous input ("pre-roll"), without affecting the speed calculation. You should ideally feed it one block-length + one interval
// Provide previous input ("pre-roll") to smoothly change the input location without interrupting the output. This doesn't do any calculation, just copies intput to a buffer.
// You should ideally feed it `seekLength()` frames of input, unless it's directly after a `.reset()` (in which case `.outputSeek()` might be a better choice)
template<class Inputs>
void seek(Inputs &&inputs, int inputSamples, double playbackRate) {
tmpBuffer.resize(0);
@ -155,6 +162,59 @@ struct SignalsmithStretch {
didSeek = true;
seekTimeFactor = (playbackRate*stft.defaultInterval() > 1) ? 1/playbackRate : stft.defaultInterval();
}
int seekLength() const {
return int(stft.blockSamples() + stft.defaultInterval());
}
// Moves the input position *and* pre-calculates some output, so that the next samples returned from `.process()` are aligned to the beginning of the sample.
// The time-stretch rate is inferred from `inputLength`, so use `.outputSeekLength()` to get a correct value for that.
template<class Inputs>
void outputSeek(Inputs &&inputs, int inputLength) {
// TODO: add fade-out parameter to avoid clicks, instead of doing a full reset
reset();
// Assume we've been handed enough surplus input to produce `outputLatency()` samples of pre-roll
int surplusInput = std::max<int>(inputLength - inputLatency(), 0);
Sample playbackRate = surplusInput/Sample(outputLatency());
// Move the input position to the start of the sound
int seekSamples = inputLength - surplusInput;
seek(inputs, seekSamples, playbackRate);
// Awkward proxy classes to avoid copying/allocating anything
struct OffsetInput {
Inputs &inputs;
int offset;
struct Channel {
Inputs &inputs;
int channel;
int offset;
Sample operator[](int i) {
return Sample(inputs[channel][i + offset]);
}
};
Channel operator[](int c) {
return {inputs, c, offset};
}
} offsetInput{inputs, seekSamples};
tmpBuffer.resize(outputLatency()*channels);
struct PreRollOutput {
Sample *samples;
int length;
Sample * operator[](int c) {
return samples + c*length;
}
} preRollOutput{tmpBuffer.data(), outputLatency()};
// Use the surplus input to produce pre-roll output
process(offsetInput, surplusInput, preRollOutput, outputLatency());
// TODO: put the thing down, flip it and reverse it
}
int outputSeekLength(Sample playbackRate) const {
return inputLatency() + playbackRate*outputLatency();
}
template<class Inputs, class Outputs>
void process(Inputs &&inputs, int inputSamples, Outputs &&outputs, int outputSamples) {
@ -383,7 +443,6 @@ struct SignalsmithStretch {
stft.readOutput(c, plainOutput, tmpBuffer.data());
auto &&outputChannel = outputs[c];
for (int i = 0; i < plainOutput; ++i) {
// TODO: plain output should be gain-
outputChannel[i] = tmpBuffer[i];
}
tmpBuffer.resize(foldedBackOutput);
@ -392,7 +451,7 @@ struct SignalsmithStretch {
outputChannel[outputSamples - 1 - i] -= tmpBuffer[i];
}
}
stft.reset(0.1);
stft.reset(0.1f);
// Reset the phase-vocoder stuff, so the next block gets a fresh start
for (int c = 0; c < channels; ++c) {