Add Modal backend for audio mixdown

gpu/modal_deployments/deploy-all.sh

@@ -131,6 +131,15 @@ if [ -z "$DIARIZER_URL" ]; then
 fi
 echo "  -> $DIARIZER_URL"
 
+echo ""
+echo "Deploying mixdown (CPU audio processing)..."
+MIXDOWN_URL=$(modal deploy reflector_mixdown.py 2>&1 | grep -o 'https://[^ ]*web.modal.run' | head -1)
+if [ -z "$MIXDOWN_URL" ]; then
+    echo "Error: Failed to deploy mixdown. Check Modal dashboard for details."
+    exit 1
+fi
+echo "  -> $MIXDOWN_URL"
+
 # --- Output Configuration ---
 echo ""
 echo "=========================================="
@@ -147,4 +156,8 @@ echo ""
 echo "DIARIZATION_BACKEND=modal"
 echo "DIARIZATION_URL=$DIARIZER_URL"
 echo "DIARIZATION_MODAL_API_KEY=$API_KEY"
+echo ""
+echo "MIXDOWN_BACKEND=modal"
+echo "MIXDOWN_URL=$MIXDOWN_URL"
+echo "MIXDOWN_MODAL_API_KEY=$API_KEY"
 echo "# --- End Modal Configuration ---"

gpu/modal_deployments/reflector_mixdown.py

@@ -0,0 +1,379 @@
+"""
+Reflector GPU backend - audio mixdown
+======================================
+
+CPU-intensive audio mixdown service for combining multiple audio tracks.
+Uses PyAV filter graph (amix) for high-quality audio mixing.
+"""
+
+import os
+import tempfile
+import time
+from fractions import Fraction
+
+import modal
+
+MIXDOWN_TIMEOUT = 900  # 15 minutes
+SCALEDOWN_WINDOW = 60  # 1 minute idle before shutdown
+
+app = modal.App("reflector-mixdown")
+
+# CPU-based image (no GPU needed for audio processing)
+image = (
+    modal.Image.debian_slim(python_version="3.12")
+    .apt_install("ffmpeg")  # Required by PyAV
+    .pip_install(
+        "av==13.1.0",  # PyAV for audio processing
+        "requests==2.32.3",  # HTTP for presigned URL downloads/uploads
+        "fastapi==0.115.12",  # API framework
+    )
+)
+
+
+@app.function(
+    cpu=4.0,  # 4 CPU cores for audio processing
+    timeout=MIXDOWN_TIMEOUT,
+    scaledown_window=SCALEDOWN_WINDOW,
+    secrets=[modal.Secret.from_name("reflector-gpu")],
+    image=image,
+)
+@modal.concurrent(max_inputs=10)
+@modal.asgi_app()
+def web():
+    import logging
+    import secrets
+    import shutil
+
+    import av
+    import requests
+    from av.audio.resampler import AudioResampler
+    from fastapi import Depends, FastAPI, HTTPException, status
+    from fastapi.security import OAuth2PasswordBearer
+    from pydantic import BaseModel
+
+    # Setup logging
+    logging.basicConfig(
+        level=logging.INFO, format="%(asctime)s - %(levelname)s - %(message)s"
+    )
+    logger = logging.getLogger(__name__)
+
+    app = FastAPI()
+    oauth2_scheme = OAuth2PasswordBearer(tokenUrl="token")
+
+    # Validate API key exists at startup
+    API_KEY = os.environ.get("REFLECTOR_GPU_APIKEY")
+    if not API_KEY:
+        raise RuntimeError("REFLECTOR_GPU_APIKEY not configured in Modal secrets")
+
+    def apikey_auth(apikey: str = Depends(oauth2_scheme)):
+        # Use constant-time comparison to prevent timing attacks
+        if secrets.compare_digest(apikey, API_KEY):
+            return
+        raise HTTPException(
+            status_code=status.HTTP_401_UNAUTHORIZED,
+            detail="Invalid API key",
+            headers={"WWW-Authenticate": "Bearer"},
+        )
+
+    class MixdownRequest(BaseModel):
+        track_urls: list[str]
+        output_url: str
+        target_sample_rate: int = 48000
+        expected_duration_sec: float | None = None
+
+    class MixdownResponse(BaseModel):
+        duration_ms: float
+        tracks_mixed: int
+        audio_uploaded: bool
+
+    def download_track(url: str, temp_dir: str, index: int) -> str:
+        """Download track from presigned URL to temp file using streaming."""
+        logger.info(f"Downloading track {index + 1}")
+        response = requests.get(url, stream=True, timeout=300)
+
+        if response.status_code == 404:
+            raise HTTPException(status_code=404, detail=f"Track {index} not found")
+        if response.status_code == 403:
+            raise HTTPException(
+                status_code=403, detail=f"Track {index} presigned URL expired"
+            )
+
+        response.raise_for_status()
+
+        temp_path = os.path.join(temp_dir, f"track_{index}.webm")
+        total_bytes = 0
+        with open(temp_path, "wb") as f:
+            for chunk in response.iter_content(chunk_size=8192):
+                if chunk:
+                    f.write(chunk)
+                    total_bytes += len(chunk)
+
+        logger.info(f"Track {index + 1} downloaded: {total_bytes} bytes")
+        return temp_path
+
+    def mixdown_tracks_modal(
+        track_paths: list[str],
+        output_path: str,
+        target_sample_rate: int,
+        expected_duration_sec: float | None,
+        logger,
+    ) -> float:
+        """Mix multiple audio tracks using PyAV filter graph.
+
+        Args:
+            track_paths: List of local file paths to audio tracks
+            output_path: Local path for output MP3 file
+            target_sample_rate: Sample rate for output (Hz)
+            expected_duration_sec: Optional fallback duration if container metadata unavailable
+            logger: Logger instance for progress tracking
+
+        Returns:
+            Duration in milliseconds
+        """
+        logger.info(f"Starting mixdown of {len(track_paths)} tracks")
+
+        # Build PyAV filter graph: N abuffer -> amix -> aformat -> sink
+        graph = av.filter.Graph()
+        inputs = []
+
+        for idx in range(len(track_paths)):
+            args = (
+                f"time_base=1/{target_sample_rate}:"
+                f"sample_rate={target_sample_rate}:"
+                f"sample_fmt=s32:"
+                f"channel_layout=stereo"
+            )
+            in_ctx = graph.add("abuffer", args=args, name=f"in{idx}")
+            inputs.append(in_ctx)
+
+        mixer = graph.add("amix", args=f"inputs={len(inputs)}:normalize=0", name="mix")
+        fmt = graph.add(
+            "aformat",
+            args=f"sample_fmts=s32:channel_layouts=stereo:sample_rates={target_sample_rate}",
+            name="fmt",
+        )
+        sink = graph.add("abuffersink", name="out")
+
+        # Connect inputs to mixer (no delays for Modal implementation)
+        for idx, in_ctx in enumerate(inputs):
+            in_ctx.link_to(mixer, 0, idx)
+
+        mixer.link_to(fmt)
+        fmt.link_to(sink)
+        graph.configure()
+
+        # Open all containers
+        containers = []
+        try:
+            for i, path in enumerate(track_paths):
+                try:
+                    c = av.open(path)
+                    containers.append(c)
+                except Exception as e:
+                    logger.warning(
+                        f"Failed to open container {i}: {e}",
+                    )
+
+            if not containers:
+                raise ValueError("Could not open any track containers")
+
+            # Calculate total duration for progress reporting
+            max_duration_sec = 0.0
+            for c in containers:
+                if c.duration is not None:
+                    dur_sec = c.duration / av.time_base
+                    max_duration_sec = max(max_duration_sec, dur_sec)
+            if max_duration_sec == 0.0 and expected_duration_sec:
+                max_duration_sec = expected_duration_sec
+
+            # Setup output container
+            out_container = av.open(output_path, "w", format="mp3")
+            out_stream = out_container.add_stream("libmp3lame", rate=target_sample_rate)
+
+            decoders = [c.decode(audio=0) for c in containers]
+            active = [True] * len(decoders)
+            resamplers = [
+                AudioResampler(format="s32", layout="stereo", rate=target_sample_rate)
+                for _ in decoders
+            ]
+
+            current_max_time = 0.0
+            last_log_time = time.monotonic()
+            start_time = time.monotonic()
+
+            total_duration = 0
+
+            while any(active):
+                for i, (dec, is_active) in enumerate(zip(decoders, active)):
+                    if not is_active:
+                        continue
+                    try:
+                        frame = next(dec)
+                    except StopIteration:
+                        active[i] = False
+                        inputs[i].push(None)  # Signal end of stream
+                        continue
+
+                    if frame.sample_rate != target_sample_rate:
+                        continue
+
+                    # Progress logging (every 5 seconds)
+                    if frame.time is not None:
+                        current_max_time = max(current_max_time, frame.time)
+                        now = time.monotonic()
+                        if now - last_log_time >= 5.0:
+                            elapsed = now - start_time
+                            if max_duration_sec > 0:
+                                progress_pct = min(
+                                    100.0, (current_max_time / max_duration_sec) * 100
+                                )
+                                logger.info(
+                                    f"Mixdown progress: {progress_pct:.1f}% @ {current_max_time:.1f}s (elapsed: {elapsed:.1f}s)"
+                                )
+                            else:
+                                logger.info(
+                                    f"Mixdown progress: @ {current_max_time:.1f}s (elapsed: {elapsed:.1f}s)"
+                                )
+                            last_log_time = now
+
+                    out_frames = resamplers[i].resample(frame) or []
+                    for rf in out_frames:
+                        rf.sample_rate = target_sample_rate
+                        rf.time_base = Fraction(1, target_sample_rate)
+                        inputs[i].push(rf)
+
+                    # Pull mixed frames from sink and encode
+                    while True:
+                        try:
+                            mixed = sink.pull()
+                        except Exception:
+                            break
+                        mixed.sample_rate = target_sample_rate
+                        mixed.time_base = Fraction(1, target_sample_rate)
+
+                        # Encode and mux
+                        for packet in out_stream.encode(mixed):
+                            out_container.mux(packet)
+                            total_duration += packet.duration
+
+            # Flush remaining frames from filter graph
+            while True:
+                try:
+                    mixed = sink.pull()
+                except Exception:
+                    break
+                mixed.sample_rate = target_sample_rate
+                mixed.time_base = Fraction(1, target_sample_rate)
+
+                for packet in out_stream.encode(mixed):
+                    out_container.mux(packet)
+                    total_duration += packet.duration
+
+            # Flush encoder
+            for packet in out_stream.encode():
+                out_container.mux(packet)
+                total_duration += packet.duration
+
+            # Calculate duration in milliseconds
+            if total_duration > 0:
+                # Use the same calculation as AudioFileWriterProcessor
+                duration_ms = round(
+                    float(total_duration * out_stream.time_base * 1000), 2
+                )
+            else:
+                duration_ms = 0.0
+
+            out_container.close()
+            logger.info(f"Mixdown complete: duration={duration_ms}ms")
+
+        finally:
+            # Cleanup all containers
+            for c in containers:
+                if c is not None:
+                    try:
+                        c.close()
+                    except Exception:
+                        pass
+
+        return duration_ms
+
+    @app.post("/v1/audio/mixdown", dependencies=[Depends(apikey_auth)])
+    def mixdown(request: MixdownRequest) -> MixdownResponse:
+        """Mix multiple audio tracks into a single MP3 file.
+
+        Tracks are downloaded from presigned S3 URLs, mixed using PyAV,
+        and uploaded to a presigned S3 PUT URL.
+        """
+        if not request.track_urls:
+            raise HTTPException(status_code=400, detail="No track URLs provided")
+
+        logger.info(f"Mixdown request: {len(request.track_urls)} tracks")
+
+        temp_dir = tempfile.mkdtemp()
+        temp_files = []
+        output_mp3_path = None
+
+        try:
+            # Download all tracks
+            for i, url in enumerate(request.track_urls):
+                temp_path = download_track(url, temp_dir, i)
+                temp_files.append(temp_path)
+
+            # Mix tracks
+            output_mp3_path = os.path.join(temp_dir, "mixed.mp3")
+            duration_ms = mixdown_tracks_modal(
+                temp_files,
+                output_mp3_path,
+                request.target_sample_rate,
+                request.expected_duration_sec,
+                logger,
+            )
+
+            # Upload result to S3
+            logger.info("Uploading result to S3")
+            file_size = os.path.getsize(output_mp3_path)
+            with open(output_mp3_path, "rb") as f:
+                upload_response = requests.put(
+                    request.output_url, data=f, timeout=300
+                )
+
+            if upload_response.status_code == 403:
+                raise HTTPException(
+                    status_code=403, detail="Output presigned URL expired"
+                )
+
+            upload_response.raise_for_status()
+            logger.info(f"Upload complete: {file_size} bytes")
+
+            return MixdownResponse(
+                duration_ms=duration_ms,
+                tracks_mixed=len(request.track_urls),
+                audio_uploaded=True,
+            )
+
+        except HTTPException:
+            raise
+        except Exception as e:
+            logger.error(f"Mixdown failed: {e}", exc_info=True)
+            raise HTTPException(status_code=500, detail=f"Mixdown failed: {str(e)}")
+
+        finally:
+            # Cleanup temp files
+            for temp_path in temp_files:
+                try:
+                    os.unlink(temp_path)
+                except Exception as e:
+                    logger.warning(f"Failed to cleanup temp file {temp_path}: {e}")
+
+            if output_mp3_path and os.path.exists(output_mp3_path):
+                try:
+                    os.unlink(output_mp3_path)
+                except Exception as e:
+                    logger.warning(f"Failed to cleanup output file {output_mp3_path}: {e}")
+
+            try:
+                shutil.rmtree(temp_dir)
+            except Exception as e:
+                logger.warning(f"Failed to cleanup temp directory {temp_dir}: {e}")
+
+    return app

server/reflector/hatchet/workflows/daily_multitrack_pipeline.py

@@ -489,7 +489,7 @@ async def process_tracks(input: PipelineInput, ctx: Context) -> ProcessTracksRes
 )
 @with_error_handling(TaskName.MIXDOWN_TRACKS)
 async def mixdown_tracks(input: PipelineInput, ctx: Context) -> MixdownResult:
-    """Mix all padded tracks into single audio file using PyAV (same as Celery)."""
+    """Mix all padded tracks into single audio file using PyAV or Modal backend."""
     ctx.log("mixdown_tracks: mixing padded tracks into single audio file")
 
     track_result = ctx.task_output(process_tracks)
@@ -513,7 +513,7 @@ async def mixdown_tracks(input: PipelineInput, ctx: Context) -> MixdownResult:
 
     storage = _spawn_storage()
 
-    # Presign URLs on demand (avoids stale URLs on workflow replay)
+    # Presign URLs for padded tracks (same expiration for both backends)
     padded_urls = []
     for track_info in padded_tracks:
         if track_info.key:
@@ -534,33 +534,104 @@ async def mixdown_tracks(input: PipelineInput, ctx: Context) -> MixdownResult:
         logger.error("Mixdown failed - no decodable audio frames found")
         raise ValueError("No decodable audio frames in any track")
 
-    output_path = tempfile.mktemp(suffix=".mp3")
+    output_key = f"{input.transcript_id}/audio.mp3"
-    duration_ms_callback_capture_container = [0.0]
 
-    async def capture_duration(d):
+    # Conditional: Modal or local backend
-        duration_ms_callback_capture_container[0] = d
+    if settings.MIXDOWN_BACKEND == "modal":
+        ctx.log("mixdown_tracks: using Modal backend")
 
-    writer = AudioFileWriterProcessor(path=output_path, on_duration=capture_duration)
+        # Presign PUT URL for output (Modal will upload directly)
+        output_url = await storage.get_file_url(
+            output_key,
+            operation="put_object",
+            expires_in=PRESIGNED_URL_EXPIRATION_SECONDS,
+        )
 
-    await mixdown_tracks_pyav(
+        from reflector.processors.audio_mixdown_modal import (  # noqa: PLC0415
-        valid_urls,
+            AudioMixdownModalProcessor,
-        writer,
+        )
-        target_sample_rate,
-        offsets_seconds=None,
-        logger=logger,
-        progress_callback=make_audio_progress_logger(ctx, TaskName.MIXDOWN_TRACKS),
-        expected_duration_sec=recording_duration if recording_duration > 0 else None,
-    )
-    await writer.flush()
 
-    file_size = Path(output_path).stat().st_size
+        try:
-    storage_path = f"{input.transcript_id}/audio.mp3"
+            processor = AudioMixdownModalProcessor()
+            result = await processor.mixdown(
+                track_urls=valid_urls,
+                output_url=output_url,
+                target_sample_rate=target_sample_rate,
+                expected_duration_sec=recording_duration
+                if recording_duration > 0
+                else None,
+            )
+            duration_ms = result.duration_ms
+            tracks_mixed = result.tracks_mixed
 
-    with open(output_path, "rb") as mixed_file:
+            ctx.log(
-        await storage.put_file(storage_path, mixed_file)
+                f"mixdown_tracks: Modal returned duration={duration_ms}ms, tracks={tracks_mixed}"
+            )
+        except httpx.HTTPStatusError as e:
+            error_detail = e.response.text if hasattr(e.response, "text") else str(e)
+            logger.error(
+                "[Hatchet] Modal mixdown HTTP error",
+                transcript_id=input.transcript_id,
+                status_code=e.response.status_code if hasattr(e, "response") else None,
+                error=error_detail,
+            )
+            raise RuntimeError(
+                f"Modal mixdown failed with HTTP {e.response.status_code}: {error_detail}"
+            )
+        except httpx.TimeoutException:
+            logger.error(
+                "[Hatchet] Modal mixdown timeout",
+                transcript_id=input.transcript_id,
+                timeout=settings.MIXDOWN_TIMEOUT,
+            )
+            raise RuntimeError(
+                f"Modal mixdown timeout after {settings.MIXDOWN_TIMEOUT}s"
+            )
+        except ValueError as e:
+            logger.error(
+                "[Hatchet] Modal mixdown validation error",
+                transcript_id=input.transcript_id,
+                error=str(e),
+            )
+            raise
+    else:
+        ctx.log("mixdown_tracks: using local backend")
 
-    Path(output_path).unlink(missing_ok=True)
+        # Existing local implementation
+        output_path = tempfile.mktemp(suffix=".mp3")
+        duration_ms_callback_capture_container = [0.0]
 
+        async def capture_duration(d):
+            duration_ms_callback_capture_container[0] = d
+
+        writer = AudioFileWriterProcessor(
+            path=output_path, on_duration=capture_duration
+        )
+
+        await mixdown_tracks_pyav(
+            valid_urls,
+            writer,
+            target_sample_rate,
+            offsets_seconds=None,
+            logger=logger,
+            progress_callback=make_audio_progress_logger(ctx, TaskName.MIXDOWN_TRACKS),
+            expected_duration_sec=recording_duration
+            if recording_duration > 0
+            else None,
+        )
+        await writer.flush()
+
+        file_size = Path(output_path).stat().st_size
+        with open(output_path, "rb") as mixed_file:
+            await storage.put_file(output_key, mixed_file)
+
+        Path(output_path).unlink(missing_ok=True)
+        duration_ms = duration_ms_callback_capture_container[0]
+        tracks_mixed = len(valid_urls)
+
+        ctx.log(f"mixdown_tracks: local mixdown uploaded {file_size} bytes")
+
+    # Update DB (same for both backends)
     async with fresh_db_connection():
         from reflector.db.transcripts import transcripts_controller  # noqa: PLC0415
 
@@ -570,12 +641,12 @@ async def mixdown_tracks(input: PipelineInput, ctx: Context) -> MixdownResult:
                 transcript, {"audio_location": "storage"}
             )
 
-    ctx.log(f"mixdown_tracks complete: uploaded {file_size} bytes to {storage_path}")
+    ctx.log(f"mixdown_tracks complete: uploaded to {output_key}")
 
     return MixdownResult(
-        audio_key=storage_path,
+        audio_key=output_key,
-        duration=duration_ms_callback_capture_container[0],
+        duration=duration_ms,
-        tracks_mixed=len(valid_urls),
+        tracks_mixed=tracks_mixed,
     )
 
 

server/reflector/processors/audio_mixdown_modal.py

@@ -0,0 +1,89 @@
+"""
+Modal.com backend for audio mixdown.
+
+Uses Modal's CPU containers to offload audio mixing from Hatchet workers.
+Communicates via presigned S3 URLs for both input and output.
+"""
+
+import httpx
+from pydantic import BaseModel
+
+from reflector.settings import settings
+
+
+class MixdownResponse(BaseModel):
+    """Response from Modal mixdown endpoint."""
+
+    duration_ms: float
+    tracks_mixed: int
+    audio_uploaded: bool
+
+
+class AudioMixdownModalProcessor:
+    """Audio mixdown processor using Modal.com CPU backend.
+
+    Sends track URLs (presigned GET) and output URL (presigned PUT) to Modal.
+    Modal handles download, mixdown via PyAV, and upload.
+    """
+
+    def __init__(self, modal_api_key: str | None = None):
+        if not settings.MIXDOWN_URL:
+            raise ValueError("MIXDOWN_URL required to use AudioMixdownModalProcessor")
+
+        self.mixdown_url = settings.MIXDOWN_URL + "/v1"
+        self.timeout = settings.MIXDOWN_TIMEOUT
+        self.modal_api_key = modal_api_key or settings.MIXDOWN_MODAL_API_KEY
+
+        if not self.modal_api_key:
+            raise ValueError(
+                "MIXDOWN_MODAL_API_KEY required to use AudioMixdownModalProcessor"
+            )
+
+    async def mixdown(
+        self,
+        track_urls: list[str],
+        output_url: str,
+        target_sample_rate: int,
+        expected_duration_sec: float | None = None,
+    ) -> MixdownResponse:
+        """Mix multiple audio tracks via Modal backend.
+
+        Args:
+            track_urls: List of presigned GET URLs for audio tracks (non-empty)
+            output_url: Presigned PUT URL for output MP3
+            target_sample_rate: Sample rate for output (Hz, must be positive)
+            expected_duration_sec: Optional fallback duration if container metadata unavailable
+
+        Returns:
+            MixdownResponse with duration_ms, tracks_mixed, audio_uploaded
+
+        Raises:
+            ValueError: If track_urls is empty or target_sample_rate invalid
+            httpx.HTTPStatusError: On HTTP errors (404, 403, 500, etc.)
+            httpx.TimeoutException: On timeout
+        """
+        # Validate inputs
+        if not track_urls:
+            raise ValueError("track_urls cannot be empty")
+        if target_sample_rate <= 0:
+            raise ValueError(
+                f"target_sample_rate must be positive, got {target_sample_rate}"
+            )
+        if expected_duration_sec is not None and expected_duration_sec < 0:
+            raise ValueError(
+                f"expected_duration_sec cannot be negative, got {expected_duration_sec}"
+            )
+
+        async with httpx.AsyncClient(timeout=self.timeout) as client:
+            response = await client.post(
+                f"{self.mixdown_url}/audio/mixdown",
+                headers={"Authorization": f"Bearer {self.modal_api_key}"},
+                json={
+                    "track_urls": track_urls,
+                    "output_url": output_url,
+                    "target_sample_rate": target_sample_rate,
+                    "expected_duration_sec": expected_duration_sec,
+                },
+            )
+            response.raise_for_status()
+            return MixdownResponse(**response.json())

server/reflector/settings.py

@@ -98,6 +98,17 @@ class Settings(BaseSettings):
     # Diarization: local pyannote.audio
     DIARIZATION_PYANNOTE_AUTH_TOKEN: str | None = None
 
+    # Audio Mixdown
+    # backends:
+    #   - local: in-process PyAV mixdown (runs in same process as Hatchet worker)
+    #   - modal: HTTP API client to Modal.com CPU container
+    MIXDOWN_BACKEND: str = "local"
+    MIXDOWN_URL: str | None = None
+    MIXDOWN_TIMEOUT: int = 900  # 15 minutes
+
+    # Mixdown: modal backend
+    MIXDOWN_MODAL_API_KEY: str | None = None
+
     # Sentry
     SENTRY_DSN: str | None = None