1 files changed, 233 insertions, 0 deletions
diff --git a/apps/web/src/media/waveform-summary.ts b/apps/web/src/media/waveform-summary.ts
new file mode 100644
index 00000000..03a0059c
--- /dev/null
+++ b/apps/web/src/media/waveform-summary.ts
@@ -0,0 +1,233 @@
+"use client";
+
+import { getSourceTimeAtClipTime } from "@/retime";
+import type { RetimeConfig } from "@/timeline";
+
+const RMS_ANALYSIS_WINDOW_SECONDS = 0.02;
+const DEFAULT_SOURCE_WAVEFORM_BUCKET_SIZE = 128;
+
+function computePeakBuckets({
+	buffer,
+	buckets,
+}: {
+	buffer: AudioBuffer;
+	buckets: SampleBucket[];
+}): number[] {
+	const channels = buffer.numberOfChannels;
+	const channelData: Float32Array[] = Array.from({ length: channels }, (_, c) =>
+		buffer.getChannelData(c),
+	);
+
+	return buckets.map(({ bucketStart, bucketEnd }) => {
+		let peak = 0;
+		for (let c = 0; c < channels; c++) {
+			const data = channelData[c];
+			for (let j = bucketStart; j < bucketEnd; j++) {
+				const abs = Math.abs(data[j] ?? 0);
+				if (abs > peak) {
+					peak = abs;
+				}
+			}
+		}
+		return peak;
+	});
+}
+
+export interface SampleBucket {
+	bucketStart: number;
+	bucketEnd: number;
+}
+
+export interface SourceWaveformSummary {
+	sourceKey: string;
+	sampleRate: number;
+	totalSamples: number;
+	bucketSize: number;
+	amplitudes: Float32Array;
+}
+
+export function buildWaveformSourceKey({
+	kind,
+	id,
+}: {
+	kind: "media" | "library";
+	id: string;
+}): string {
+	return `${kind}:${id}`;
+}
+
+export function buildSourceWaveformSummary({
+	sourceKey,
+	buffer,
+	bucketSize = DEFAULT_SOURCE_WAVEFORM_BUCKET_SIZE,
+}: {
+	sourceKey: string;
+	buffer: AudioBuffer;
+	bucketSize?: number;
+}): SourceWaveformSummary {
+	const safeBucketSize = Math.max(1, Math.floor(bucketSize));
+	const bucketCount = Math.max(1, Math.ceil(buffer.length / safeBucketSize));
+	const amplitudes = computePeakBuckets({
+		buffer,
+		buckets: Array.from({ length: bucketCount }, (_, bucketIndex) => {
+			const bucketStart = bucketIndex * safeBucketSize;
+			const bucketEnd = Math.min(buffer.length, bucketStart + safeBucketSize);
+			return { bucketStart, bucketEnd };
+		}),
+	});
+
+	return {
+		sourceKey,
+		sampleRate: buffer.sampleRate,
+		totalSamples: buffer.length,
+		bucketSize: safeBucketSize,
+		amplitudes: Float32Array.from(amplitudes),
+	};
+}
+
+export function buildWaveformSampleBuckets({
+	clipLeftPx,
+	clipRightPx,
+	barCount,
+	pixelsPerSecond,
+	clipDurationSec,
+	sourceStartSec,
+	retime,
+	sampleRate,
+	maxSampleExclusive,
+	barStepPx,
+}: {
+	clipLeftPx: number;
+	clipRightPx: number;
+	barCount: number;
+	pixelsPerSecond: number;
+	clipDurationSec: number;
+	sourceStartSec: number;
+	retime?: RetimeConfig;
+	sampleRate: number;
+	maxSampleExclusive: number;
+	barStepPx: number;
+}): SampleBucket[] {
+	return Array.from({ length: barCount }, (_, index) => {
+		const bucketLeftPx = clipLeftPx + index * barStepPx;
+		const bucketRightPx = Math.min(clipRightPx, bucketLeftPx + barStepPx);
+		const clipStartSec = Math.max(
+			0,
+			Math.min(clipDurationSec, bucketLeftPx / pixelsPerSecond),
+		);
+		const clipEndSec = Math.max(
+			clipStartSec,
+			Math.min(clipDurationSec, bucketRightPx / pixelsPerSecond),
+		);
+		const sourceBucketStartSec =
+			sourceStartSec +
+			getSourceTimeAtClipTime({
+				clipTime: clipStartSec,
+				retime,
+			});
+		const sourceBucketEndSec =
+			sourceStartSec +
+			getSourceTimeAtClipTime({
+				clipTime: clipEndSec,
+				retime,
+			});
+
+		return {
+			bucketStart: Math.max(0, Math.floor(sourceBucketStartSec * sampleRate)),
+			bucketEnd: Math.min(
+				maxSampleExclusive,
+				Math.max(0, Math.ceil(sourceBucketEndSec * sampleRate)),
+			),
+		};
+	});
+}
+
+export function sampleSourceWaveformSummary({
+	summary,
+	buckets,
+}: {
+	summary: SourceWaveformSummary;
+	buckets: SampleBucket[];
+}): number[] {
+	return buckets.map(({ bucketStart, bucketEnd }) => {
+		if (bucketEnd <= bucketStart) {
+			return 0;
+		}
+
+		const startIndex = Math.max(
+			0,
+			Math.floor(bucketStart / summary.bucketSize),
+		);
+		const endIndex = Math.min(
+			summary.amplitudes.length,
+			Math.max(startIndex + 1, Math.ceil(bucketEnd / summary.bucketSize)),
+		);
+
+		let maxAmplitude = 0;
+		for (let i = startIndex; i < endIndex; i++) {
+			const amplitude = summary.amplitudes[i] ?? 0;
+			if (amplitude > maxAmplitude) {
+				maxAmplitude = amplitude;
+			}
+		}
+
+		return maxAmplitude;
+	});
+}
+
+export function computeRmsBuckets({
+	buffer,
+	buckets,
+}: {
+	buffer: AudioBuffer;
+	buckets: SampleBucket[];
+}): number[] {
+	const channels = buffer.numberOfChannels;
+	const maxWindowLength = Math.max(
+		1,
+		Math.floor(buffer.sampleRate * RMS_ANALYSIS_WINDOW_SECONDS),
+	);
+
+	const channelData: Float32Array[] = new Array(channels);
+	for (let c = 0; c < channels; c++) {
+		channelData[c] = buffer.getChannelData(c);
+	}
+
+	const result = new Array<number>(buckets.length);
+
+	for (let i = 0; i < buckets.length; i++) {
+		const { bucketStart, bucketEnd } = buckets[i];
+		const bucketLength = bucketEnd - bucketStart;
+		if (bucketLength <= 0) {
+			result[i] = 0;
+			continue;
+		}
+
+		const windowLength = Math.max(1, Math.min(bucketLength, maxWindowLength));
+		let maxMeanSquare = 0;
+
+		for (let winStart = bucketStart; winStart < bucketEnd; ) {
+			const winEnd = Math.min(winStart + windowLength, bucketEnd);
+			const n = winEnd - winStart;
+			if (n > 0) {
+				let sum = 0;
+				for (let c = 0; c < channels; c++) {
+					const data = channelData[c];
+					for (let j = winStart; j < winEnd; j++) {
+						const v = data[j];
+						sum += v * v;
+					}
+				}
+				const meanSquare = sum / (n * channels);
+				if (meanSquare > maxMeanSquare) {
+					maxMeanSquare = meanSquare;
+				}
+			}
+			winStart = winEnd;
+		}
+
+		result[i] = Math.sqrt(maxMeanSquare);
+	}
+
+	return result;
+}