feat: Created ChapterMarkers overlay component, added RegionsPlugin cha…

- "frontend/src/components/ChapterMarkers.tsx"
- "frontend/src/components/PlayerControls.tsx"
- "frontend/src/components/AudioWaveform.tsx"
- "frontend/src/pages/WatchPage.tsx"
- "frontend/src/App.css"

GSD-Task: S05/T03

frontend/src/App.css

@@ -6050,6 +6050,67 @@ a.app-footer__about:hover,
   font-weight: 600;
 }
 
+/* ── Seek container + Chapter markers ──────────────────────────────────────── */
+
+.player-controls__seek-container {
+  position: relative;
+  flex: 1;
+  display: flex;
+  align-items: center;
+}
+
+.player-controls__seek-container .player-controls__seek {
+  width: 100%;
+}
+
+.chapter-markers {
+  position: absolute;
+  top: 0;
+  left: 0;
+  right: 0;
+  bottom: 0;
+  pointer-events: none;
+}
+
+.chapter-marker__tick {
+  position: absolute;
+  width: 3px;
+  height: 100%;
+  background: var(--color-accent, #22d3ee);
+  opacity: 0.6;
+  pointer-events: all;
+  cursor: pointer;
+  transform: translateX(-50%);
+  border: none;
+  padding: 0;
+  font: inherit;
+}
+
+.chapter-marker__tick:hover {
+  opacity: 1;
+}
+
+.chapter-marker__tooltip {
+  position: absolute;
+  bottom: 100%;
+  left: 50%;
+  transform: translateX(-50%);
+  background: var(--color-bg-surface, #1e293b);
+  color: var(--text-primary, #e2e8f0);
+  padding: 4px 8px;
+  border-radius: 4px;
+  font-size: 0.75rem;
+  white-space: nowrap;
+  opacity: 0;
+  pointer-events: none;
+  transition: opacity 150ms;
+  margin-bottom: 4px;
+}
+
+.chapter-marker__tick:hover .chapter-marker__tooltip {
+  opacity: 1;
+}
+
 /* ── Responsive: player controls ───────────────────────────────────────────── */
 
 @media (max-width: 640px) {

frontend/src/components/AudioWaveform.tsx

@@ -1,18 +1,22 @@
 import { useEffect, useRef } from "react";
 import WaveSurfer from "wavesurfer.js";
+import RegionsPlugin from "wavesurfer.js/dist/plugins/regions.esm.js";
 import type { MediaSyncState } from "../hooks/useMediaSync";
+import type { Chapter } from "../api/videos";
 
 interface AudioWaveformProps {
   mediaSync: MediaSyncState;
   src: string;
+  chapters?: Chapter[];
 }
 
 /**
  * Audio-only waveform visualiser powered by wavesurfer.js.
  * Renders a hidden <audio> element owned by useMediaSync and an
  * interactive waveform. Used when no video URL is available.
+ * Optionally displays chapter regions via the RegionsPlugin.
  */
-export default function AudioWaveform({ mediaSync, src }: AudioWaveformProps) {
+export default function AudioWaveform({ mediaSync, src, chapters }: AudioWaveformProps) {
   const containerRef = useRef<HTMLDivElement | null>(null);
   const wsRef = useRef<WaveSurfer | null>(null);
 
@@ -21,6 +25,8 @@ export default function AudioWaveform({ mediaSync, src }: AudioWaveformProps) {
     const audio = mediaSync.videoRef.current as HTMLAudioElement | null;
     if (!container || !audio) return;
 
+    const regions = RegionsPlugin.create();
+
     const ws = WaveSurfer.create({
       container,
       media: audio,
@@ -32,17 +38,34 @@ export default function AudioWaveform({ mediaSync, src }: AudioWaveformProps) {
       barGap: 1,
       barRadius: 2,
       backend: "MediaElement",
+      plugins: [regions],
     });
 
     wsRef.current = ws;
 
+    // Add chapter regions once waveform is ready
+    if (chapters && chapters.length > 0) {
+      ws.on("ready", () => {
+        for (const ch of chapters) {
+          regions.addRegion({
+            start: ch.start_time,
+            end: ch.end_time,
+            content: ch.title,
+            color: "rgba(0, 255, 209, 0.1)",
+            drag: false,
+            resize: false,
+          });
+        }
+      });
+    }
+
     return () => {
       ws.destroy();
       wsRef.current = null;
     };
-    // Re-create when src changes
+    // Re-create when src or chapters change
     // eslint-disable-next-line react-hooks/exhaustive-deps
-  }, [src]);
+  }, [src, chapters]);
 
   return (
     <div className="audio-waveform">

frontend/src/components/ChapterMarkers.tsx

@@ -0,0 +1,39 @@
+import type { Chapter } from "../api/videos";
+
+interface ChapterMarkersProps {
+  chapters: Chapter[];
+  duration: number;
+  onSeek: (time: number) => void;
+}
+
+/**
+ * Absolutely-positioned overlay that renders tick marks on the seek bar
+ * for each chapter. Ticks are clickable and show a tooltip on hover.
+ */
+export default function ChapterMarkers({ chapters, duration, onSeek }: ChapterMarkersProps) {
+  if (!duration || chapters.length === 0) return null;
+
+  return (
+    <div className="chapter-markers">
+      {chapters.map((ch) => {
+        const leftPct = (ch.start_time / duration) * 100;
+        return (
+          <button
+            key={ch.id}
+            className="chapter-marker__tick"
+            style={{ left: `${leftPct}%` }}
+            onClick={(e) => {
+              e.stopPropagation();
+              onSeek(ch.start_time);
+            }}
+            aria-label={`Jump to chapter: ${ch.title}`}
+            title={ch.title}
+            type="button"
+          >
+            <span className="chapter-marker__tooltip">{ch.title}</span>
+          </button>
+        );
+      })}
+    </div>
+  );
+}

frontend/src/components/PlayerControls.tsx

@@ -1,10 +1,14 @@
 import { useCallback, useEffect } from "react";
 import type { MediaSyncState } from "../hooks/useMediaSync";
+import type { Chapter } from "../api/videos";
+import ChapterMarkers from "./ChapterMarkers";
 
 interface PlayerControlsProps {
   mediaSync: MediaSyncState;
   /** Ref to the container element for fullscreen requests */
   containerRef?: React.RefObject<HTMLElement | null>;
+  /** Optional chapter markers to overlay on the seek bar */
+  chapters?: Chapter[];
 }
 
 const SPEED_OPTIONS = [0.5, 0.75, 1, 1.25, 1.5, 2] as const;
@@ -16,7 +20,7 @@ function formatTime(seconds: number): string {
   return `${m}:${s.toString().padStart(2, "0")}`;
 }
 
-export default function PlayerControls({ mediaSync, containerRef }: PlayerControlsProps) {
+export default function PlayerControls({ mediaSync, containerRef, chapters }: PlayerControlsProps) {
   const {
     currentTime,
     duration,
@@ -121,19 +125,24 @@ export default function PlayerControls({ mediaSync, containerRef }: PlayerContro
         {formatTime(currentTime)} / {formatTime(duration)}
       </span>
 
-      {/* Seek bar */}
-      <input
-        type="range"
-        className="player-controls__seek"
-        min={0}
-        max={duration || 0}
-        step={0.1}
-        value={currentTime}
-        onChange={handleSeek}
-        disabled={seekDisabled}
-        aria-label="Seek"
-        style={{ "--progress": `${seekProgress}%` } as React.CSSProperties}
-      />
+      {/* Seek bar with chapter markers */}
+      <div className="player-controls__seek-container">
+        <input
+          type="range"
+          className="player-controls__seek"
+          min={0}
+          max={duration || 0}
+          step={0.1}
+          value={currentTime}
+          onChange={handleSeek}
+          disabled={seekDisabled}
+          aria-label="Seek"
+          style={{ "--progress": `${seekProgress}%` } as React.CSSProperties}
+        />
+        {chapters && chapters.length > 0 && (
+          <ChapterMarkers chapters={chapters} duration={duration} onSeek={seekTo} />
+        )}
+      </div>
 
       {/* Speed selector */}
       <div className="player-controls__speed" role="group" aria-label="Playback speed">

frontend/src/pages/WatchPage.tsx

@@ -2,9 +2,9 @@ import { useEffect, useState } from "react";
 import { useParams, useSearchParams, Link } from "react-router-dom";
 import { useDocumentTitle } from "../hooks/useDocumentTitle";
 import { useMediaSync } from "../hooks/useMediaSync";
-import { fetchVideo, fetchTranscript } from "../api/videos";
+import { fetchVideo, fetchTranscript, fetchChapters } from "../api/videos";
 import { BASE } from "../api/client";
-import type { VideoDetail, TranscriptSegment } from "../api/videos";
+import type { VideoDetail, TranscriptSegment, Chapter } from "../api/videos";
 import { ApiError } from "../api/client";
 import VideoPlayer from "../components/VideoPlayer";
 import AudioWaveform from "../components/AudioWaveform";
@@ -24,6 +24,7 @@ export default function WatchPage() {
   const [loading, setLoading] = useState(true);
   const [error, setError] = useState<string | null>(null);
   const [transcriptError, setTranscriptError] = useState(false);
+  const [chapters, setChapters] = useState<Chapter[]>([]);
 
   const mediaSync = useMediaSync();
 
@@ -61,6 +62,14 @@ export default function WatchPage() {
         if (!cancelled) setTranscriptError(true);
       }
 
+      // Fetch chapters — non-critical, fail silently
+      try {
+        const c = await fetchChapters(videoId);
+        if (!cancelled) setChapters(c.chapters);
+      } catch {
+        // chapters are optional — ignore errors
+      }
+
       if (!cancelled) setLoading(false);
     })();
 
@@ -117,9 +126,9 @@ export default function WatchPage() {
               mediaSync={mediaSync}
             />
           ) : (
-            <AudioWaveform src={streamUrl} mediaSync={mediaSync} />
+            <AudioWaveform src={streamUrl} mediaSync={mediaSync} chapters={chapters} />
           )}
-          <PlayerControls mediaSync={mediaSync} />
+          <PlayerControls mediaSync={mediaSync} chapters={chapters} />
         </div>
 
         <TranscriptSidebar