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| author | Maze Winther <mazewinther@gmail.com> | 2026-04-20 11:31:17 +0200 |
|---|---|---|
| committer | Maze Winther <mazewinther@gmail.com> | 2026-04-20 11:31:17 +0200 |
| commit | 3e89d2998588f8e35c524e523ba2ee853f0f6475 (patch) | |
| tree | 57221f96c1259b3b07e3ddf8c1adefc502b9d8eb /apps/web/src/retime/audio-stretch.ts | |
| parent | 729d10592f4e802f91c555c309ff3ba4b119f843 (diff) | |
| download | opencut-3e89d2998588f8e35c524e523ba2ee853f0f6475.tar.gz | |
refactor: restructure files to their domains, new preview overlay system, and dep graph
Diffstat (limited to 'apps/web/src/retime/audio-stretch.ts')
| -rw-r--r-- | apps/web/src/retime/audio-stretch.ts | 182 |
1 files changed, 182 insertions, 0 deletions
diff --git a/apps/web/src/retime/audio-stretch.ts b/apps/web/src/retime/audio-stretch.ts new file mode 100644 index 00000000..7df67f36 --- /dev/null +++ b/apps/web/src/retime/audio-stretch.ts @@ -0,0 +1,182 @@ +import { PitchShifter } from "soundtouchjs";
+import { clampRetimeRate, shouldMaintainPitch } from "@/retime/rate";
+import type { RetimeConfig } from "@/timeline";
+import { getSourceTimeAtClipTime } from "./resolve";
+
+const RATE_EPSILON = 1e-6;
+
+function sampleLinear({
+ channelData,
+ position,
+}: {
+ channelData: Float32Array;
+ position: number;
+}): number {
+ if (position <= 0) {
+ return channelData[0] ?? 0;
+ }
+ const lower = Math.floor(position);
+ const upper = Math.min(channelData.length - 1, lower + 1);
+ if (lower >= channelData.length) {
+ return 0;
+ }
+ const fraction = position - lower;
+ return channelData[lower] * (1 - fraction) + channelData[upper] * fraction;
+}
+
+function buildResampledBuffer({
+ audioContext,
+ sourceBuffer,
+ trimStart,
+ clipDuration,
+ targetSampleRate,
+ retime,
+}: {
+ audioContext: BaseAudioContext;
+ sourceBuffer: AudioBuffer;
+ trimStart: number;
+ clipDuration: number;
+ targetSampleRate: number;
+ retime?: RetimeConfig;
+}): AudioBuffer {
+ const outputLength = Math.max(1, Math.ceil(clipDuration * targetSampleRate));
+ const numChannels = Math.max(1, Math.min(2, sourceBuffer.numberOfChannels));
+ const outputBuffer = audioContext.createBuffer(
+ numChannels,
+ outputLength,
+ targetSampleRate,
+ );
+
+ for (let channel = 0; channel < numChannels; channel++) {
+ const sourceData = sourceBuffer.getChannelData(
+ Math.min(channel, sourceBuffer.numberOfChannels - 1),
+ );
+ const outputData = outputBuffer.getChannelData(channel);
+
+ for (let i = 0; i < outputLength; i++) {
+ const clipTime = i / targetSampleRate;
+ const sourceTime =
+ trimStart + getSourceTimeAtClipTime({ clipTime, retime });
+ outputData[i] = sampleLinear({
+ channelData: sourceData,
+ position: sourceTime * sourceBuffer.sampleRate,
+ });
+ }
+ }
+
+ return outputBuffer;
+}
+
+async function buildPitchPreservedBuffer({
+ sourceBuffer,
+ trimStart,
+ clipDuration,
+ rate,
+ targetSampleRate,
+}: {
+ sourceBuffer: AudioBuffer;
+ trimStart: number;
+ clipDuration: number;
+ rate: number;
+ targetSampleRate: number;
+}): Promise<AudioBuffer> {
+ const nativeSampleRate = sourceBuffer.sampleRate;
+ const sourceDuration = clipDuration * rate;
+ const startSample = Math.max(0, Math.floor(trimStart * nativeSampleRate));
+ const numSourceSamples = Math.max(
+ 1,
+ Math.ceil(sourceDuration * nativeSampleRate),
+ );
+ const available = Math.max(0, sourceBuffer.length - startSample);
+ const actualSamples = Math.max(1, Math.min(numSourceSamples, available));
+ const numChannels = Math.max(1, Math.min(2, sourceBuffer.numberOfChannels));
+
+ // Resample to targetSampleRate first — soundtouchjs reads raw channel data
+ // and does not respect the source buffer's native sample rate.
+ const resampledLength = Math.max(
+ 1,
+ Math.ceil(sourceDuration * targetSampleRate),
+ );
+ const resampleCtx = new OfflineAudioContext(
+ numChannels,
+ resampledLength,
+ targetSampleRate,
+ );
+ const nativeBuffer = resampleCtx.createBuffer(
+ numChannels,
+ actualSamples,
+ nativeSampleRate,
+ );
+
+ for (let ch = 0; ch < numChannels; ch++) {
+ const src = sourceBuffer.getChannelData(
+ Math.min(ch, sourceBuffer.numberOfChannels - 1),
+ );
+ nativeBuffer.copyToChannel(
+ src.subarray(startSample, startSample + actualSamples),
+ ch,
+ );
+ }
+
+ const resampleSourceNode = resampleCtx.createBufferSource();
+ resampleSourceNode.buffer = nativeBuffer;
+ resampleSourceNode.connect(resampleCtx.destination);
+ resampleSourceNode.start(0);
+ const resampledBuffer = await resampleCtx.startRendering();
+
+ const outputSamples = Math.max(
+ 1,
+ Math.ceil(clipDuration * targetSampleRate),
+ );
+ const stretchCtx = new OfflineAudioContext(
+ numChannels,
+ outputSamples,
+ targetSampleRate,
+ );
+ const shifter = new PitchShifter(stretchCtx, resampledBuffer, 4096);
+ shifter.tempo = rate;
+ shifter.pitch = 1;
+ shifter.connect(stretchCtx.destination);
+ return stretchCtx.startRendering();
+}
+
+export async function renderRetimedBuffer({
+ audioContext,
+ sourceBuffer,
+ trimStart,
+ clipDuration,
+ retime,
+ maintainPitch = false,
+}: {
+ audioContext: BaseAudioContext;
+ sourceBuffer: AudioBuffer;
+ trimStart: number;
+ clipDuration: number;
+ retime?: RetimeConfig;
+ maintainPitch?: boolean;
+}): Promise<AudioBuffer> {
+ const targetSampleRate = audioContext.sampleRate;
+ const rate = clampRetimeRate({ rate: retime?.rate ?? 1 });
+ const usePitchPreservation =
+ shouldMaintainPitch({ rate, maintainPitch }) &&
+ Math.abs(rate - 1) > RATE_EPSILON;
+
+ if (usePitchPreservation) {
+ return buildPitchPreservedBuffer({
+ sourceBuffer,
+ trimStart,
+ clipDuration,
+ rate,
+ targetSampleRate,
+ });
+ }
+
+ return buildResampledBuffer({
+ audioContext,
+ sourceBuffer,
+ trimStart,
+ clipDuration,
+ targetSampleRate,
+ retime,
+ });
+}
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