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feat(pcm-player): implement OLA time-stretch algo
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@yume-chan
yume-chan committed Sep 26, 2023
1 parent bde5e2c commit 3ecf231
Showing 1 changed file with 138 additions and 43 deletions.
181 changes: 138 additions & 43 deletions libraries/pcm-player/worker/worker.ts
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Original file line number Diff line number Diff line change
@@ -1,4 +1,14 @@
const SAMPLE_RATE = 48000;
const INPUT_HOP_SIZE = 3000;
const SCALE = 0.9;
const OUTPUT_HOP_SIZE = (INPUT_HOP_SIZE * SCALE) | 0;

const WINDOW_SIZE = 6000;
const WINDOW_WEIGHT_TABLE = new Float32Array(WINDOW_SIZE);
for (let i = 0; i < WINDOW_SIZE / 2; i += 1) {
const value = Math.sin((i / WINDOW_SIZE) * Math.PI);
WINDOW_WEIGHT_TABLE[i] = value;
WINDOW_WEIGHT_TABLE[WINDOW_SIZE - i - 1] = value;
}

abstract class SourceProcessor<T>
extends AudioWorkletProcessor
Expand All @@ -7,13 +17,16 @@ abstract class SourceProcessor<T>
#chunks: T[] = [];
#chunkSampleCounts: number[] = [];
#totalSampleCount = 0;

#speedUp = false;
#readOffset = 0;
#inputOffset = 0;
#outputOffset = 0;

constructor() {
super();
this.port.onmessage = (event) => {
// Throw away old chunks when buffer is exceeding 0.2s
while (this.#totalSampleCount > SAMPLE_RATE * 0.2) {
while (this.#totalSampleCount > 16000) {
this.#chunks.shift();
const count = this.#chunkSampleCounts.shift()!;
this.#totalSampleCount -= count;
Expand All @@ -25,52 +38,111 @@ abstract class SourceProcessor<T>
this.#chunkSampleCounts.push(length);
this.#totalSampleCount += length;

// Speed up when buffer is exceeding 0.1s
if (this.#totalSampleCount > SAMPLE_RATE * 0.1) {
if (!this.#speedUp && this.#totalSampleCount > 8000) {
this.#speedUp = true;
this.#readOffset = 0;
this.#inputOffset = 0;
this.#outputOffset = 0;
}
};
}

protected abstract createSource(data: ArrayBuffer[]): [T, number];

process(_inputs: Float32Array[][], outputs: Float32Array[][]) {
// Stop speeding up when buffer is below 0.05s
if (this.#speedUp && this.#totalSampleCount < 3000) {
this.#speedUp = false;
}

const outputLeft = outputs[0]![0]!;
const outputRight = outputs[0]![1]!;
const outputLength = outputLeft.length;
let outputIndex = 0;

// Stop speeding up when buffer is below 0.05s
if (this.#speedUp && this.#totalSampleCount < SAMPLE_RATE * 0.05) {
this.#speedUp = false;
if (this.#speedUp) {
for (let i = 0; i < outputLength; i += 1) {
let totalWeight = 0;

const firstWindow = Math.max(
0,
Math.floor(
(this.#outputOffset - WINDOW_SIZE) / OUTPUT_HOP_SIZE,
) + 1,
);

let inWindowIndex =
this.#outputOffset - firstWindow * OUTPUT_HOP_SIZE;
let inputIndex = firstWindow * INPUT_HOP_SIZE + inWindowIndex;

while (inputIndex > 0 && inWindowIndex >= 0) {
const [left, right] = this.#read(
inputIndex - this.#readOffset,
);

const weight = WINDOW_WEIGHT_TABLE[inWindowIndex]!;
outputLeft[i] += left * weight;
outputRight[i] += right * weight;
totalWeight += weight;

inputIndex += INPUT_HOP_SIZE - OUTPUT_HOP_SIZE;
inWindowIndex -= OUTPUT_HOP_SIZE;
inWindowIndex %= WINDOW_SIZE;
}

if (totalWeight > 0) {
outputLeft[i] /= totalWeight;
outputRight[i] /= totalWeight;
}

this.#outputOffset += 1;
if (firstWindow > 0) {
this.#outputOffset -= OUTPUT_HOP_SIZE;
this.#readOffset -= INPUT_HOP_SIZE;
this.#inputOffset += (1 - SCALE) * INPUT_HOP_SIZE;
}
}

this.#inputOffset += outputLength;
const firstChunkSampleCount = this.#chunkSampleCounts[0]!;
if (
firstChunkSampleCount !== undefined &&
this.#inputOffset >= firstChunkSampleCount
) {
this.#chunks.shift();
this.#chunkSampleCounts.shift();
this.#totalSampleCount -= firstChunkSampleCount;
this.#readOffset += firstChunkSampleCount;
this.#inputOffset -= firstChunkSampleCount;
}
} else {
this.#copyChunks(outputLeft, outputRight);
}

const sourceIndexStep = this.#speedUp ? 1.02 : 1;
let sourceIndex = 0;
return true;
}

#copyChunks(outputLeft: Float32Array, outputRight: Float32Array) {
let outputIndex = 0;
const outputLength = outputLeft.length;

while (this.#chunks.length > 0 && outputIndex < outputLength) {
const beginSourceIndex = sourceIndex | 0;

let source: T | undefined = this.#chunks[0];
[source, sourceIndex, outputIndex] = this.copyChunk(
sourceIndex,
sourceIndexStep,
let consumedSampleCount = 0;
[source, consumedSampleCount, outputIndex] = this.copyChunk(
source!,
outputLeft,
outputRight,
outputLength,
outputIndex,
);

const consumedSampleCount = (sourceIndex | 0) - beginSourceIndex;
this.#totalSampleCount -= consumedSampleCount;
sourceIndex -= consumedSampleCount;

if (source) {
// Output full
this.#chunks[0] = source;
this.#chunkSampleCounts[0]! -= consumedSampleCount;
return true;
return;
}

this.#chunks.shift();
Expand All @@ -84,13 +156,24 @@ abstract class SourceProcessor<T>
} samples`,
);
}
}

return true;
#read(offset: number): [number, number] {
for (let i = 0; i < this.#chunks.length; i += 1) {
const length = this.#chunkSampleCounts[i]!;

if (offset < length) {
return this.read(this.#chunks[i]!, offset);
}

offset -= length;
}
return [0, 0];
}

protected abstract read(source: T, offset: number): [number, number];

protected abstract copyChunk(
sourceIndex: number,
sourceIndexStep: number,
source: T,
outputLeft: Float32Array,
outputRight: Float32Array,
Expand All @@ -108,9 +191,14 @@ class Int16SourceProcessor
return [source, source.length / 2];
}

protected override read(
source: Int16Array,
offset: number,
): [number, number] {
return [source[offset * 2]! / 0x8000, source[offset * 2 + 1]! / 0x8000];
}

protected override copyChunk(
sourceIndex: number,
sourceIndexStep: number,
source: Int16Array,
outputLeft: Float32Array,
outputRight: Float32Array,
Expand All @@ -122,28 +210,27 @@ class Int16SourceProcessor
outputIndex: number,
] {
const sourceLength = source.length;
let sourceSampleIndex = sourceIndex << 1;
let sourceSampleIndex = 0;

while (sourceSampleIndex < sourceLength) {
outputLeft[outputIndex] = source[sourceSampleIndex]! / 0x8000;
outputRight[outputIndex] = source[sourceSampleIndex + 1]! / 0x8000;

sourceIndex += sourceIndexStep;
sourceSampleIndex = sourceIndex << 1;
sourceSampleIndex += 2;
outputIndex += 1;

if (outputIndex === outputLength) {
return [
sourceSampleIndex < sourceLength
? source.subarray(sourceSampleIndex)
: undefined,
sourceIndex,
sourceSampleIndex / 2,
outputIndex,
];
}
}

return [undefined, sourceIndex, outputIndex];
return [undefined, sourceSampleIndex / 2, outputIndex];
}
}

Expand All @@ -155,9 +242,14 @@ class Float32SourceProcessor extends SourceProcessor<Float32Array> {
return [source, source.length / 2];
}

protected override read(
source: Float32Array,
offset: number,
): [number, number] {
return [source[offset * 2]!, source[offset * 2 + 1]!];
}

protected override copyChunk(
sourceIndex: number,
sourceIndexStep: number,
source: Float32Array,
outputLeft: Float32Array,
outputRight: Float32Array,
Expand All @@ -169,28 +261,27 @@ class Float32SourceProcessor extends SourceProcessor<Float32Array> {
outputIndex: number,
] {
const sourceLength = source.length;
let sourceSampleIndex = sourceIndex << 1;
let sourceSampleIndex = 0;

while (sourceSampleIndex < sourceLength) {
outputLeft[outputIndex] = source[sourceSampleIndex]!;
outputRight[outputIndex] = source[sourceSampleIndex + 1]!;

sourceIndex += sourceIndexStep;
sourceSampleIndex = sourceIndex << 1;
sourceSampleIndex += 2;
outputIndex += 1;

if (outputIndex === outputLength) {
return [
sourceSampleIndex < sourceLength
? source.subarray(sourceSampleIndex)
: undefined,
sourceIndex,
sourceSampleIndex / 2,
outputIndex,
];
}
}

return [undefined, sourceIndex, outputIndex];
return [undefined, sourceSampleIndex / 2, outputIndex];
}
}

Expand All @@ -202,9 +293,14 @@ class Float32PlanerSourceProcessor extends SourceProcessor<Float32Array[]> {
return [source, source[0]!.length];
}

protected override read(
source: Float32Array[],
offset: number,
): [number, number] {
return [source[0]![offset]!, source[1]![offset]!];
}

protected override copyChunk(
sourceIndex: number,
sourceIndexStep: number,
source: Float32Array[],
outputLeft: Float32Array,
outputRight: Float32Array,
Expand All @@ -218,14 +314,13 @@ class Float32PlanerSourceProcessor extends SourceProcessor<Float32Array[]> {
const sourceLeft = source[0]!;
const sourceRight = source[1]!;
const sourceLength = sourceLeft.length;
let sourceSampleIndex = sourceIndex | 0;
let sourceSampleIndex = 0;

while (sourceSampleIndex < sourceLength) {
outputLeft[outputIndex] = sourceLeft[sourceSampleIndex]!;
outputRight[outputIndex] = sourceRight[sourceSampleIndex]!;

sourceIndex += sourceIndexStep;
sourceSampleIndex = sourceIndex | 0;
sourceSampleIndex += 1;
outputIndex += 1;

if (outputIndex === outputLength) {
Expand All @@ -235,13 +330,13 @@ class Float32PlanerSourceProcessor extends SourceProcessor<Float32Array[]> {
channel.subarray(sourceSampleIndex),
)
: undefined,
sourceIndex,
sourceSampleIndex,
outputIndex,
];
}
}

return [undefined, sourceIndex, outputIndex];
return [undefined, sourceSampleIndex, outputIndex];
}
}

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