feat(tools): 2.0 phase 5 wave 5b - ai pool: ocr-pdf, transcription, background composites (5 tools) (#226)

apps/api/src/lib/subtitle-format.ts

@@ -0,0 +1,36 @@
+export interface TranscriptSegment {
+  startS: number;
+  endS: number;
+  text: string;
+}
+
+function pad(n: number, w: number): string {
+  return String(n).padStart(w, "0");
+}
+
+function stamp(totalS: number, msSep: string): string {
+  const ms = Math.max(0, Math.round(totalS * 1000));
+  const h = Math.floor(ms / 3600000);
+  const m = Math.floor((ms % 3600000) / 60000);
+  const s = Math.floor((ms % 60000) / 1000);
+  const frac = ms % 1000;
+  return `${pad(h, 2)}:${pad(m, 2)}:${pad(s, 2)}${msSep}${pad(frac, 3)}`;
+}
+
+/** SubRip: 1-based counters, comma millisecond separator. */
+export function toSrt(segments: TranscriptSegment[]): string {
+  return segments
+    .map(
+      (seg, i) =>
+        `${i + 1}\n${stamp(seg.startS, ",")} --> ${stamp(seg.endS, ",")}\n${seg.text.trim()}\n`,
+    )
+    .join("\n");
+}
+
+/** WebVTT: header + dot millisecond separator, no counters. */
+export function toVtt(segments: TranscriptSegment[]): string {
+  const body = segments
+    .map((seg) => `${stamp(seg.startS, ".")} --> ${stamp(seg.endS, ".")}\n${seg.text.trim()}\n`)
+    .join("\n");
+  return `WEBVTT\n\n${body}`;
+}