feat: play cached TTS audio immediately on auto-start if already generated

scraper/internal/server/server.go

@@ -134,6 +134,8 @@ func (s *Server) ListenAndServe(ctx context.Context) error {
 		`{"error":"audio generation timed out"}`,
 	)
 	mux.Handle("POST /ui/audio/{slug}/{n}", audioGenHandler)
+	// Status route: returns the proxy URL if audio was already generated, 404 otherwise.
+	mux.HandleFunc("GET /ui/audio/{slug}/{n}", s.handleAudioStatus)
 	// Proxy route: fetches the generated file from Kokoro /v1/download/{filename}.
 	mux.HandleFunc("GET /ui/audio-proxy/{slug}/{n}", s.handleAudioProxy)
 
@@ -355,6 +357,39 @@ func (s *Server) writeAudioResponse(w http.ResponseWriter, slug string, n int, v
 	})
 }
 
+// handleAudioStatus handles GET /ui/audio/{slug}/{n}.
+// Returns the proxy URL if audio was already generated this session, 404 otherwise.
+func (s *Server) handleAudioStatus(w http.ResponseWriter, r *http.Request) {
+	slug := r.PathValue("slug")
+	n, err := strconv.Atoi(r.PathValue("n"))
+	if err != nil || n < 1 {
+		http.Error(w, `{"error":"invalid chapter"}`, http.StatusBadRequest)
+		return
+	}
+	voice := r.URL.Query().Get("voice")
+	if voice == "" {
+		voice = s.kokoroVoice
+	}
+	speedStr := r.URL.Query().Get("speed")
+	speed := 1.0
+	if speedStr != "" {
+		if v, err := strconv.ParseFloat(speedStr, 64); err == nil && v > 0 {
+			speed = v
+		}
+	}
+
+	cacheKey := fmt.Sprintf("%s/%d/%s/%.2f", slug, n, voice, speed)
+	s.audioMu.Lock()
+	filename, ok := s.audioCache[cacheKey]
+	s.audioMu.Unlock()
+
+	if !ok {
+		http.Error(w, `{"error":"not generated"}`, http.StatusNotFound)
+		return
+	}
+	s.writeAudioResponse(w, slug, n, voice, speed, filename)
+}
+
 // handleAudioProxy handles GET /ui/audio-proxy/{slug}/{n}.
 // It looks up the Kokoro download filename for this chapter (voice/speed) and
 // proxies GET /v1/download/{filename} from the Kokoro server back to the browser.

scraper/internal/server/ui.go

@@ -2922,21 +2922,43 @@ const chapterTmpl = `
     navigator.mediaSession.setActionHandler('seekto', function(d) { if (isFinite(d.seekTime)) { audio.currentTime = d.seekTime; updateSeek(); } });
   }
 
+  function loadAndPlay(url) {
+    // Always set autoplay=true before load(): the browser needs this hint set
+    // synchronously before load() regardless of whether we got here via a user
+    // gesture or a programmatic trigger (e.g. chapter transition).  The canplay
+    // handler will call play() as well, but autoplay on the element is the only
+    // reliable path after an async fetch where the gesture stack is gone.
+    audio.autoplay = true;
+    audio.src = url; audio.load();
+    audio.playbackRate = getSpeed();
+    registerMediaSession();
+  }
+
   function startAudio(autoplay) {
     setGenerating();
     highlightPara(0);
-    generateAudio(CHAPTER_N, function (url) {
-      if (stale()) return;
-      // Always set autoplay=true before load(): the browser needs this hint set
-      // synchronously before load() regardless of whether we got here via a user
-      // gesture or a programmatic trigger (e.g. chapter transition).  The canplay
-      // handler will call play() as well, but autoplay on the element is the only
-      // reliable path after an async fetch where the gesture stack is gone.
-      audio.autoplay = true;
-      audio.src = url; audio.load();
-      audio.playbackRate = getSpeed();
-      registerMediaSession();
-    });
+    // Check if audio was already generated for this chapter this session.
+    // If so, play it directly without re-generating.
+    fetch('/ui/audio/' + SLUG + '/' + CHAPTER_N + '?voice=' + encodeURIComponent(voiceSel.value) + '&speed=1')
+      .then(function(res) {
+        if (stale()) return;
+        if (res.ok) {
+          return res.json().then(function(data) {
+            if (stale()) return;
+            if (data && data.url) { loadAndPlay(data.url); return; }
+            throw new Error('no url in response');
+          });
+        }
+        // Not cached yet — fall through to generation.
+        generateAudio(CHAPTER_N, function(url) {
+          if (stale()) return;
+          loadAndPlay(url);
+        });
+      })
+      .catch(function(e) {
+        if (stale()) return;
+        setError(e.message);
+      });
   }
 
   window.ttsToggle = function () {