Preload audio as Blob for instant seeking; generate Opus playback file; delete original upload after extraction

- Download full audio as Blob on mount so seeking is instant (no network range-requests)
- Remove readyState guard from playAt() that was silently blocking seek attempts
- Add disabled/ready state to SessionReel for reliable click-to-seek
- Generate 48kbps Opus playback file during extraction (~65MB for 3hrs vs 1.5GB lossless)
- Serve Opus first in audio endpoint, then original upload, then extracted WAV
- Delete original upload after successful transcription to reclaim storage
- Reorder extract_audio checks so retry works without the original file
- Fix Back links on Speakers and Notes pages to go to home

backend/app/main.py

@@ -84,13 +84,21 @@ def get_audio(session_id: str):
     if not row:
         raise HTTPException(404, "Session not found")
 
-    # Prefer the original uploaded file — it's a compressed format the browser
-    # can seek in efficiently.  Fall back to the extracted WAV.
+    # Priority: Opus playback > original upload > extracted WAV.
+    # The Opus file is tiny (~65 MB for 3 hours) so the frontend's Blob
+    # download completes in seconds on any modern connection.
     candidates = []
+
+    if row["audio_path"]:
+        opus = Path(row["audio_path"]).with_suffix(".opus")
+        if opus.exists():
+            candidates.append(opus)
+
     if row["video_path"]:
         p = Path(row["video_path"])
         if p.exists():
             candidates.append(p)
+
     if row["audio_path"]:
         p = Path(row["audio_path"])
         if p.exists():

backend/app/pipeline/audio.py

@@ -9,13 +9,13 @@ log = get_logger(__name__)
 
 def extract_audio(video_path: Path, audio_path: Path) -> Path:
     """Extract 16kHz mono wav from any video/audio container."""
-    if not video_path.exists():
-        raise AudioExtractionError(f"Uploaded file not found on disk at {video_path}. It may not have finished uploading, or the upload volume isn't mounted correctly.")
-
     if audio_path.exists():
         log.info("Audio already extracted at %s, skipping", audio_path)
         return audio_path
 
+    if not video_path.exists():
+        raise AudioExtractionError(f"Uploaded file not found on disk at {video_path}. It may not have finished uploading, or the upload volume isn't mounted correctly.")
+
     log.info("Extracting audio: %s -> %s", video_path, audio_path)
     result = subprocess.run(
         [
@@ -33,3 +33,30 @@ def extract_audio(video_path: Path, audio_path: Path) -> Path:
             f"This usually means the file is corrupt or not a supported format. Last output:\n{stderr_tail}"
         )
     return audio_path
+
+
+def generate_playback_audio(video_path: Path, playback_path: Path) -> Path | None:
+    """Generate a compressed Opus file for browser playback (~48 kbps).
+
+    This is done alongside the WAV extraction so the frontend can download a
+    small file for instant-seeking Blob playback.  Existing sessions that lack
+    the Opus file will fall back to the original upload or the extracted WAV.
+    """
+    if playback_path.exists():
+        log.info("Playback audio already exists at %s, skipping", playback_path)
+        return playback_path
+
+    log.info("Generating playback audio: %s -> %s", video_path, playback_path)
+    result = subprocess.run(
+        [
+            "ffmpeg", "-y", "-i", str(video_path),
+            "-vn", "-c:a", "libopus", "-b:a", "48k",
+            str(playback_path),
+        ],
+        capture_output=True, text=True,
+    )
+    if result.returncode != 0:
+        stderr_tail = "\n".join(result.stderr.strip().splitlines()[-5:])
+        log.warning("Failed to generate playback audio (non-fatal): %s", stderr_tail)
+        return None
+    return playback_path

backend/app/routers/sessions.py

@@ -8,7 +8,7 @@ from fastapi import APIRouter, UploadFile, File, Form, HTTPException
 from .. import database as db, config, jobs
 from ..config import merge_campaign_settings_with_env
 from ..errors import PipelineError
-from ..pipeline.audio import extract_audio
+from ..pipeline.audio import extract_audio, generate_playback_audio
 from ..pipeline.transcribe import transcribe_and_diarize
 
 
@@ -96,6 +96,7 @@ def _run_transcription(session_id: str, video_path: Path, audio_path: Path, tran
         progress_cb("Extracting audio...")
         try:
             extract_audio(video_path, audio_path)
+            generate_playback_audio(video_path, audio_path.with_suffix(".opus"))
             transcribe_and_diarize(
                 audio_path,
                 transcript_path,
@@ -114,6 +115,16 @@ def _run_transcription(session_id: str, video_path: Path, audio_path: Path, tran
                 (str(audio_path), str(transcript_path), session_id),
             )
 
+        # Original upload no longer needed — Opus serves playback, WAV serves
+        # re-transcription.  Reclaim storage.
+        if video_path.exists():
+            try:
+                video_path.unlink()
+                with db.tx() as conn:
+                    conn.execute("UPDATE sessions SET video_path = NULL WHERE id = ?", (session_id,))
+            except OSError:
+                pass  # non-fatal
+
     job_id = db.create_job(session_id, "transcribe")
     jobs.submit(job_id, run, requires_gpu=True)
     return job_id

frontend/src/components/SessionReel.tsx

@@ -14,35 +14,44 @@ export function SessionReel({
   duration,
   onSeek,
   currentTime,
+  disabled,
 }: {
   turns: { start: number; end: number; raw_speaker: string }[];
   duration: number;
   onSeek: (t: number) => void;
   currentTime: number;
+  disabled?: boolean;
 }) {
   const palette = useMemo(() => new Map<string, string>(), []);
   const trackRef = useRef<HTMLDivElement>(null);
 
-  const valid = duration > 0 && isFinite(duration);
+  const ready = duration > 0 && isFinite(duration);
+  const canSeek = ready && !disabled;
 
   const handleClick = (e: React.MouseEvent) => {
-    if (!trackRef.current || !valid) return;
+    if (!trackRef.current || !canSeek) return;
     const rect = trackRef.current.getBoundingClientRect();
     const frac = (e.clientX - rect.left) / rect.width;
     onSeek(Math.max(0, Math.min(duration, frac * duration)));
   };
 
-  const playheadPct = valid ? (currentTime / duration) * 100 : 0;
+  const playheadPct = ready ? (currentTime / duration) * 100 : 0;
 
   return (
     <div
       ref={trackRef}
       onClick={handleClick}
-      className={"relative h-14 rounded-md border overflow-hidden " + (valid ? "bg-deep border-white/10 cursor-pointer" : "bg-panel2 border-white/5")}
+      className={
+        "relative h-14 rounded-md border overflow-hidden transition " +
+        (canSeek
+          ? "bg-deep border-white/10 cursor-pointer hover:border-brass/40"
+          : "bg-panel2 border-white/5 cursor-default")
+      }
       role="slider"
       aria-label="Session timeline"
+      aria-disabled={disabled}
     >
-      {valid &&
+      {ready &&
         turns.map((t, i) => {
           const left = (t.start / duration) * 100;
           const width = Math.max(((t.end - t.start) / duration) * 100, 0.15);
@@ -55,10 +64,12 @@ export function SessionReel({
             />
           );
         })}
+      {ready && (
         <div
-        className="absolute top-0 bottom-0 w-px bg-ink shadow-[0_0_6px_1px_rgba(237,230,214,0.6)]"
+          className="absolute top-0 bottom-0 w-px bg-ink shadow-[0_0_6px_1px_rgba(237,230,214,0.6)] pointer-events-none transition-[left]"
           style={{ left: `${playheadPct}%` }}
         />
+      )}
     </div>
   );
 }

frontend/src/pages/Notes.tsx

@@ -15,7 +15,7 @@ export default function Notes() {
 
   return (
     <div className="max-w-3xl mx-auto py-16 px-4">
-      <Link to={`/sessions/${id}`} className="text-sm text-ink/40 hover:text-brass">&larr; Back</Link>
+      <Link to="/" className="text-sm text-ink/40 hover:text-brass">&larr; Back</Link>
       <h1 className="font-display text-3xl mt-4 mb-6">Session notes</h1>
 
       <div className="flex gap-2 mb-6">

frontend/src/pages/Speakers.tsx

@@ -17,6 +17,12 @@ export default function Speakers() {
   const [showConfirm, setShowConfirm] = useState(false);
   const audioRef = useRef<HTMLAudioElement>(null);
   const paletteRef = useRef(new Map<string, string>());
+  const blobUrlRef = useRef<string | null>(null);
+
+  const [audioLoading, setAudioLoading] = useState(true);
+  const [audioProgress, setAudioProgress] = useState(0);
+  const [totalKnown, setTotalKnown] = useState(false);
+  const [audioError, setAudioError] = useState<string | null>(null);
 
   const load = () => {
     api.getSpeakers(id!).then((sp) => {
@@ -29,15 +35,78 @@ export default function Speakers() {
   };
   useEffect(load, [id]);
 
+  useEffect(() => {
+    if (!id) return;
+    setAudioLoading(true);
+    setAudioProgress(0);
+    setTotalKnown(false);
+    setAudioError(null);
+    let cancelled = false;
+    const url = api.audioUrl(id);
+
+    (async () => {
+      try {
+        const res = await fetch(url);
+        if (!res.ok) throw new Error(`HTTP ${res.status}`);
+
+        const total = parseInt(res.headers.get("Content-Length") || "0", 10);
+        setTotalKnown(total > 0);
+        const reader = res.body!.getReader();
+        const chunks: Uint8Array[] = [];
+        let received = 0;
+
+        while (true) {
+          const { done, value } = await reader.read();
+          if (done) break;
+          chunks.push(value);
+          received += value.length;
+          if (total) setAudioProgress(received / total);
+        }
+        if (cancelled) return;
+
+        const blob = new Blob(chunks, { type: res.headers.get("Content-Type") || "audio/mpeg" });
+        const blobUrl = URL.createObjectURL(blob);
+        blobUrlRef.current = blobUrl;
+
+        const audio = audioRef.current;
+        if (!audio || cancelled) {
+          URL.revokeObjectURL(blobUrl);
+          return;
+        }
+
+        audio.src = blobUrl;
+        audio.load();
+
+        await new Promise<void>((resolve, reject) => {
+          audio.onloadedmetadata = () => resolve();
+          audio.onerror = () => reject(new Error("Audio decode failed"));
+        });
+
+        if (!cancelled) setAudioLoading(false);
+      } catch (err: any) {
+        if (!cancelled) {
+          setAudioError(err.message || "Failed to load audio");
+          setAudioLoading(false);
+        }
+      }
+    })();
+
+    return () => {
+      cancelled = true;
+      if (blobUrlRef.current) {
+        URL.revokeObjectURL(blobUrlRef.current);
+        blobUrlRef.current = null;
+      }
+    };
+  }, [id]);
+
   const save = async (raw_label: string) => {
     await api.setSpeakerName(id!, raw_label, names[raw_label] || "");
   };
 
   const playAt = (t: number) => {
     const audio = audioRef.current;
-    if (!audio) return;
-    if (audio.readyState < 2) return;
-    audio.pause();
+    if (!audio || audioLoading) return;
     audio.currentTime = t;
     const p = audio.play();
     if (p) p.catch(() => {});
@@ -75,13 +144,40 @@ export default function Speakers() {
 
   return (
     <div className="max-w-4xl mx-auto py-16 px-4">
-      <Link to={`/sessions/${id}`} className="text-sm text-ink/40 hover:text-brass">&larr; Back</Link>
+      <Link to="/" className="text-sm text-ink/40 hover:text-brass">&larr; Back</Link>
       <h1 className="font-display text-3xl mt-4 mb-2">Name your speakers</h1>
       <p className="text-ink/60 mb-6">Click anywhere on the reel to jump to that moment and hear who's talking.</p>
 
+      {audioLoading && !audioError && (
+        <div className="card p-4 mb-3">
+          <div className="flex items-center justify-between mb-2">
+            <span className="text-sm text-ink/60">Loading audio for instant playback&hellip;</span>
+            {totalKnown && (
+              <span className="text-xs font-mono text-ink/40">{Math.round(audioProgress * 100)}%</span>
+            )}
+          </div>
+          <div className="h-2 rounded-full bg-deep overflow-hidden">
+            <div
+              className={
+                "h-full rounded-full bg-brass " +
+                (totalKnown
+                  ? "transition-all duration-200"
+                  : "w-1/2 animate-pulse rounded-full")
+              }
+              style={totalKnown ? { width: `${audioProgress * 100}%` } : undefined}
+            />
+          </div>
+        </div>
+      )}
+
+      {audioError && (
+        <div className="card p-4 mb-3 border-red/40">
+          <p className="text-sm text-red-400">Failed to load audio: {audioError}</p>
+        </div>
+      )}
+
       <audio
         ref={audioRef}
-        src={api.audioUrl(id!)}
         onTimeUpdate={(e) => setCurrentTime(e.currentTarget.currentTime)}
         onLoadedMetadata={(e) => setDuration(e.currentTarget.duration)}
         controls
@@ -89,7 +185,13 @@ export default function Speakers() {
       />
 
       <div className="mb-8">
-        <SessionReel turns={turns} duration={duration} currentTime={currentTime} onSeek={playAt} />
+        <SessionReel
+          turns={turns}
+          duration={duration}
+          currentTime={currentTime}
+          onSeek={playAt}
+          disabled={audioLoading || !!audioError}
+        />
       </div>
 
       {selected.size >= 2 && (
@@ -142,7 +244,8 @@ export default function Speakers() {
                 <button
                   key={i}
                   onClick={() => playAt(s.start)}
-                  className="block text-left text-sm text-ink/60 hover:text-ink w-full truncate"
+                  disabled={audioLoading}
+                  className="block text-left text-sm text-ink/60 hover:text-ink w-full truncate disabled:opacity-30 disabled:pointer-events-none"
                 >
                   ▶ {s.text}
                 </button>