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