More FE changes

video/src/narration.ts

@@ -0,0 +1,37 @@
+import { writeFileSync } from 'node:fs';
+
+export interface NarrationCue {
+  text: string;
+  videoTimeMs: number;
+  durationMs: number;
+}
+
+/**
+ * Narration manifest writer.
+ *
+ * The runner knows the exact video-time of each narration block from the
+ * storyboard itself, so cues come in with an explicit `videoTimeMs` instead
+ * of being stamped against a wall-clock origin. That keeps the manifest in
+ * lockstep with the trimmed video even if step durations drift slightly.
+ */
+class NarrationLog {
+  private cues: NarrationCue[] = [];
+
+  reset(): void {
+    this.cues = [];
+  }
+
+  add(cue: NarrationCue): void {
+    if (cue.videoTimeMs < 0) return;
+    this.cues.push(cue);
+  }
+
+  flush(path: string, totalDurationMs: number): NarrationCue[] {
+    const sorted = [...this.cues].sort((a, b) => a.videoTimeMs - b.videoTimeMs);
+    const manifest = { totalDurationMs, cues: sorted };
+    writeFileSync(path, JSON.stringify(manifest, null, 2));
+    return sorted;
+  }
+}
+
+export const narrationLog = new NarrationLog();