feat: 1-to-1 message render + web data-lake backend

frontend/src/lib/media/playback.ts

@@ -0,0 +1,14 @@
+let current: HTMLMediaElement | null = null;
+
+export function claimPlayback(element: HTMLMediaElement) {
+  if (current && current !== element) {
+    current.pause();
+  }
+  current = element;
+}
+
+export function releasePlayback(element: HTMLMediaElement) {
+  if (current === element) {
+    current = null;
+  }
+}

frontend/src/lib/media/waveform.ts

@@ -0,0 +1,36 @@
+const BARS = 48;
+const MIN_BAR = 0.08;
+
+export async function computeWaveform(
+  url: string,
+  bars = BARS
+): Promise<number[]> {
+  const response = await fetch(url);
+  const buffer = await response.arrayBuffer();
+  const ctx = new AudioContext();
+  try {
+    const audio = await ctx.decodeAudioData(buffer);
+    const data = audio.getChannelData(0);
+    const block = Math.max(1, Math.floor(data.length / bars));
+    const peaks: number[] = [];
+    for (let i = 0; i < bars; i++) {
+      const start = i * block;
+      let max = 0;
+      for (let j = 0; j < block; j++) {
+        const value = Math.abs(data[start + j] ?? 0);
+        if (value > max) {
+          max = value;
+        }
+      }
+      peaks.push(max);
+    }
+    const norm = Math.max(...peaks, 0.0001);
+    return peaks.map((peak) => Math.max(MIN_BAR, peak / norm));
+  } finally {
+    await ctx.close();
+  }
+}
+
+export function flatWaveform(bars = BARS): number[] {
+  return Array.from({ length: bars }, () => 0.3);
+}