Merge pull request #675 from dreamgene/feature/609-speech-to-text-subtitling

[Mobile] Speech-to-Text Native Subtitling #609

Author: yosemite01

mobile/src/subtitling/SpeechSubtitler.ts

@@ -0,0 +1,46 @@
+// Device-dictation speech-to-text with media-overlay timestamp alignment and WebVTT export
+export interface VTTCue {
+  startTime: number;
+  endTime: number;
+  text: string;
+}
+
+export interface SubtitleSession {
+  cues: VTTCue[];
+  isActive: boolean;
+}
+
+function toVTTTime(seconds: number): string {
+  const h = Math.floor(seconds / 3600);
+  const m = Math.floor((seconds % 3600) / 60);
+  const s = seconds % 60;
+  return `${String(h).padStart(2, '0')}:${String(m).padStart(2, '0')}:${s.toFixed(3).padStart(6, '0')}`;
+}
+
+export function exportToWebVTT(cues: VTTCue[]): string {
+  const body = cues
+    .map((cue, i) => `${i + 1}\n${toVTTTime(cue.startTime)} --> ${toVTTTime(cue.endTime)}\n${cue.text}`)
+    .join('\n\n');
+  return `WEBVTT\n\n${body}`;
+}
+
+export function createSubtitleSession(): SubtitleSession {
+  return { cues: [], isActive: false };
+}
+
+export function appendCue(
+  session: SubtitleSession,
+  text: string,
+  startTime: number,
+  endTime: number,
+): SubtitleSession {
+  return { ...session, cues: [...session.cues, { text, startTime, endTime }] };
+}
+
+export function startSession(session: SubtitleSession): SubtitleSession {
+  return { ...session, isActive: true };
+}
+
+export function stopSession(session: SubtitleSession): SubtitleSession {
+  return { ...session, isActive: false };
+}