feat: captions on mobile

Closes #199
2026-04-30 17:14:15 -07:00
parent a6a4757a8e
commit 3051b1558f
4 changed files with 200 additions and 7 deletions
@@ -0,0 +1,49 @@
+import { useMemo } from "react";
+import type { Transcript } from "@/api/types";
+
+type Sentence = Transcript["paragraphs"][number]["sentences"][number];
+
+interface TranscriptPlaybackState {
+  /** The sentence currently being spoken, or null if between sentences */
+  activeSentence: Sentence | null;
+  /** Index of the active word within the transcript's flat words array */
+  activeWordIndex: number | null;
+}
+
+export function useTranscriptPlayback(
+  transcript: Transcript | undefined,
+  currentTime: number,
+): TranscriptPlaybackState {
+  return useMemo(() => {
+    if (!transcript) return { activeSentence: null, activeWordIndex: null };
+
+    // Find the active sentence across all paragraphs
+    let activeSentence: Sentence | null = null;
+    for (const paragraph of transcript.paragraphs) {
+      const sentence = paragraph.sentences.find(
+        (s) => currentTime >= s.start && currentTime <= s.end,
+      );
+      if (sentence) {
+        activeSentence = sentence;
+        break;
+      }
+    }
+
+    // Binary search for active word
+    const words = transcript.words;
+    let activeWordIndex: number | null = null;
+    let lo = 0;
+    let hi = words.length - 1;
+    while (lo <= hi) {
+      const mid = (lo + hi) >>> 1;
+      if (currentTime < words[mid].start) hi = mid - 1;
+      else if (currentTime > words[mid].end) lo = mid + 1;
+      else {
+        activeWordIndex = mid;
+        break;
+      }
+    }
+
+    return { activeSentence, activeWordIndex };
+  }, [transcript, currentTime]);
+}