feat: add SRT/VTT subtitle cue parser

src/core/services/subtitle-cue-parser.ts

@@ -0,0 +1,63 @@
+export interface SubtitleCue {
+  startTime: number;
+  endTime: number;
+  text: string;
+}
+
+const SRT_TIMING_PATTERN =
+  /^\s*(?:(\d{1,2}):)?(\d{2}):(\d{2})[,.](\d{1,3})\s*-->\s*(?:(\d{1,2}):)?(\d{2}):(\d{2})[,.](\d{1,3})/;
+
+function parseTimestamp(
+  hours: string | undefined,
+  minutes: string,
+  seconds: string,
+  millis: string,
+): number {
+  return (
+    Number(hours || 0) * 3600 +
+    Number(minutes) * 60 +
+    Number(seconds) +
+    Number(millis.padEnd(3, '0')) / 1000
+  );
+}
+
+export function parseSrtCues(content: string): SubtitleCue[] {
+  const cues: SubtitleCue[] = [];
+  const lines = content.split(/\r?\n/);
+  let i = 0;
+
+  while (i < lines.length) {
+    const line = lines[i]!;
+    const timingMatch = SRT_TIMING_PATTERN.exec(line);
+    if (!timingMatch) {
+      i += 1;
+      continue;
+    }
+
+    const startTime = parseTimestamp(timingMatch[1], timingMatch[2]!, timingMatch[3]!, timingMatch[4]!);
+    const endTime = parseTimestamp(timingMatch[5], timingMatch[6]!, timingMatch[7]!, timingMatch[8]!);
+
+    i += 1;
+    const textLines: string[] = [];
+    while (i < lines.length && lines[i]!.trim() !== '') {
+      textLines.push(lines[i]!);
+      i += 1;
+    }
+
+    const text = textLines.join('\n').trim();
+    if (text) {
+      cues.push({ startTime, endTime, text });
+    }
+  }
+
+  return cues;
+}
+
+// Stub exports — will be implemented in subsequent tasks
+export function parseAssCues(_content: string): SubtitleCue[] {
+  throw new Error('parseAssCues not yet implemented');
+}
+
+export function parseSubtitleCues(_content: string, _filename: string): SubtitleCue[] {
+  throw new Error('parseSubtitleCues not yet implemented');
+}