dry hatchet with celery

server/reflector/hatchet/workflows/diarization_pipeline.py

@@ -14,13 +14,10 @@ import functools
 import tempfile
 from contextlib import asynccontextmanager
 from datetime import timedelta
-from fractions import Fraction
 from pathlib import Path
 from typing import Callable
 
-import av
 import httpx
-from av.audio.resampler import AudioResampler
 from hatchet_sdk import Context
 from pydantic import BaseModel
 
@@ -30,6 +27,7 @@ from reflector.hatchet.broadcast import (
     set_status_and_broadcast,
 )
 from reflector.hatchet.client import HatchetClientManager
+from reflector.hatchet.utils import to_dict
 from reflector.hatchet.workflows.models import (
     ConsentResult,
     FinalizeResult,
@@ -62,6 +60,10 @@ from reflector.utils.audio_constants import (
     PRESIGNED_URL_EXPIRATION_SECONDS,
     WAVEFORM_SEGMENTS,
 )
+from reflector.utils.audio_mixdown import (
+    detect_sample_rate_from_tracks,
+    mixdown_tracks_pyav,
+)
 from reflector.utils.audio_waveform import get_audio_waveform
 from reflector.utils.daily import (
     filter_cam_audio_tracks,
@@ -146,17 +148,6 @@ def _get_storage():
     )
 
 
-def _to_dict(output) -> dict:
-    """Convert task output to dict, handling both dict and Pydantic model returns.
-
-    Hatchet SDK returns Pydantic models when tasks have typed return annotations,
-    but older code expects dicts. This helper normalizes the output.
-    """
-    if isinstance(output, dict):
-        return output
-    return output.model_dump()
-
-
 def with_error_handling(step_name: str, set_error_status: bool = True) -> Callable:
     """Decorator that handles task failures uniformly.
 
@@ -242,7 +233,7 @@ async def get_participants(input: PipelineInput, ctx: Context) -> ParticipantsRe
     ctx.log(f"get_participants: transcript_id={input.transcript_id}")
     logger.info("[Hatchet] get_participants", transcript_id=input.transcript_id)
 
-    recording_data = _to_dict(ctx.task_output(get_recording))
+    recording_data = to_dict(ctx.task_output(get_recording))
     mtg_session_id = recording_data.get("mtg_session_id")
 
     async with fresh_db_connection():
@@ -341,7 +332,7 @@ async def process_tracks(input: PipelineInput, ctx: Context) -> ProcessTracksRes
         transcript_id=input.transcript_id,
     )
 
-    participants_data = _to_dict(ctx.task_output(get_participants))
+    participants_data = to_dict(ctx.task_output(get_participants))
     source_language = participants_data.get("source_language", "en")
 
     child_coroutines = [
@@ -417,7 +408,7 @@ async def mixdown_tracks(input: PipelineInput, ctx: Context) -> MixdownResult:
     ctx.log("mixdown_tracks: mixing padded tracks into single audio file")
     logger.info("[Hatchet] mixdown_tracks", transcript_id=input.transcript_id)
 
-    track_data = _to_dict(ctx.task_output(process_tracks))
+    track_data = to_dict(ctx.task_output(process_tracks))
     padded_tracks_data = track_data.get("padded_tracks", [])
 
     if not padded_tracks_data:
@@ -428,7 +419,7 @@ async def mixdown_tracks(input: PipelineInput, ctx: Context) -> MixdownResult:
     # Presign URLs on demand (avoids stale URLs on workflow replay)
     padded_urls = []
     for track_info in padded_tracks_data:
-        # Handle both dict (from _to_dict) and PaddedTrackInfo
+        # Handle both dict (from to_dict) and PaddedTrackInfo
         if isinstance(track_info, dict):
             key = track_info.get("key")
             bucket = track_info.get("bucket_name")
@@ -445,149 +436,36 @@ async def mixdown_tracks(input: PipelineInput, ctx: Context) -> MixdownResult:
             )
             padded_urls.append(url)
 
-    # Use PipelineMainMultitrack.mixdown_tracks which uses PyAV filter graph
     valid_urls = [url for url in padded_urls if url]
     if not valid_urls:
         raise ValueError("No valid padded tracks to mixdown")
 
-    target_sample_rate = None
-    for url in valid_urls:
-        container = None
-        try:
-            container = av.open(url)
-            for frame in container.decode(audio=0):
-                target_sample_rate = frame.sample_rate
-                break
-        except Exception:
-            continue
-        finally:
-            if container is not None:
-                container.close()
-        if target_sample_rate:
-            break
-
+    # Detect sample rate from tracks
+    target_sample_rate = detect_sample_rate_from_tracks(valid_urls, logger=logger)
     if not target_sample_rate:
+        logger.error("Mixdown failed - no decodable audio frames found")
         raise ValueError("No decodable audio frames in any track")
 
-    # Build PyAV filter graph: N abuffer -> amix -> aformat -> sink
-    graph = av.filter.Graph()
-    inputs = []
-
-    for idx, url in enumerate(valid_urls):
-        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")
-
-    for idx, in_ctx in enumerate(inputs):
-        in_ctx.link_to(mixer, 0, idx)
-    mixer.link_to(fmt)
-    fmt.link_to(sink)
-    graph.configure()
-
+    # Create temp file and writer for MP3 output
     output_path = tempfile.mktemp(suffix=".mp3")
-    containers = []
+    duration_ms = [0.0]  # Mutable container for callback capture
 
-    try:
-        for url in valid_urls:
-            try:
-                c = av.open(
-                    url,
-                    options={
-                        "reconnect": "1",
-                        "reconnect_streamed": "1",
-                        "reconnect_delay_max": "5",
-                    },
-                )
-                containers.append(c)
-            except Exception as e:
-                logger.warning(
-                    "[Hatchet] mixdown: failed to open container",
-                    url=url,
-                    error=str(e),
-                )
+    async def capture_duration(d):
+        duration_ms[0] = d
 
-        if not containers:
-            raise ValueError("Could not open any track containers")
+    writer = AudioFileWriterProcessor(path=output_path, on_duration=capture_duration)
 
-        # Create AudioFileWriterProcessor for MP3 output with duration capture
-        duration_ms = [0.0]  # Mutable container for callback capture
-
-        async def capture_duration(d):
-            duration_ms[0] = d
-
-        writer = AudioFileWriterProcessor(
-            path=output_path, on_duration=capture_duration
-        )
-
-        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
-        ]
-
-        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)
-                    continue
-
-                if frame.sample_rate != target_sample_rate:
-                    continue
-                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)
-
-                while True:
-                    try:
-                        mixed = sink.pull()
-                    except Exception:
-                        break
-                    mixed.sample_rate = target_sample_rate
-                    mixed.time_base = Fraction(1, target_sample_rate)
-                    await writer.push(mixed)
-
-        # Flush remaining frames
-        while True:
-            try:
-                mixed = sink.pull()
-            except Exception:
-                break
-            mixed.sample_rate = target_sample_rate
-            mixed.time_base = Fraction(1, target_sample_rate)
-            await writer.push(mixed)
-
-        await writer.flush()
-
-        # Duration is captured via callback in milliseconds (from AudioFileWriterProcessor)
-
-    finally:
-        for c in containers:
-            try:
-                c.close()
-            except Exception:
-                pass
+    # Run mixdown using shared utility
+    await mixdown_tracks_pyav(
+        valid_urls,
+        writer,
+        target_sample_rate,
+        offsets_seconds=None,
+        logger=logger,
+    )
+    await writer.flush()
 
+    # Upload to storage
     file_size = Path(output_path).stat().st_size
     storage_path = f"{input.transcript_id}/audio.mp3"
 
@@ -596,6 +474,7 @@ async def mixdown_tracks(input: PipelineInput, ctx: Context) -> MixdownResult:
 
     Path(output_path).unlink(missing_ok=True)
 
+    # Update DB with audio location
     async with fresh_db_connection():
         from reflector.db.transcripts import transcripts_controller  # noqa: PLC0415
 
@@ -633,7 +512,7 @@ async def generate_waveform(input: PipelineInput, ctx: Context) -> WaveformResul
     )
 
     # Cleanup temporary padded S3 files (deferred until after mixdown)
-    track_data = _to_dict(ctx.task_output(process_tracks))
+    track_data = to_dict(ctx.task_output(process_tracks))
     created_padded_files = track_data.get("created_padded_files", [])
     if created_padded_files:
         logger.info(
@@ -653,7 +532,7 @@ async def generate_waveform(input: PipelineInput, ctx: Context) -> WaveformResul
                     error=str(result),
                 )
 
-    mixdown_data = _to_dict(ctx.task_output(mixdown_tracks))
+    mixdown_data = to_dict(ctx.task_output(mixdown_tracks))
     audio_key = mixdown_data.get("audio_key")
 
     storage = _get_storage()
@@ -703,7 +582,7 @@ async def detect_topics(input: PipelineInput, ctx: Context) -> TopicsResult:
     ctx.log("detect_topics: analyzing transcript for topics")
     logger.info("[Hatchet] detect_topics", transcript_id=input.transcript_id)
 
-    track_data = _to_dict(ctx.task_output(process_tracks))
+    track_data = to_dict(ctx.task_output(process_tracks))
     words = track_data.get("all_words", [])
     target_language = track_data.get("target_language", "en")
 
@@ -762,7 +641,7 @@ async def generate_title(input: PipelineInput, ctx: Context) -> TitleResult:
     ctx.log("generate_title: generating title from topics")
     logger.info("[Hatchet] generate_title", transcript_id=input.transcript_id)
 
-    topics_data = _to_dict(ctx.task_output(detect_topics))
+    topics_data = to_dict(ctx.task_output(detect_topics))
     topics = topics_data.get("topics", [])
 
     from reflector.db.transcripts import (  # noqa: PLC0415
@@ -813,7 +692,7 @@ async def generate_summary(input: PipelineInput, ctx: Context) -> SummaryResult:
     ctx.log("generate_summary: generating long and short summaries")
     logger.info("[Hatchet] generate_summary", transcript_id=input.transcript_id)
 
-    topics_data = _to_dict(ctx.task_output(detect_topics))
+    topics_data = to_dict(ctx.task_output(detect_topics))
     topics = topics_data.get("topics", [])
 
     from reflector.db.transcripts import (  # noqa: PLC0415
@@ -895,8 +774,8 @@ async def finalize(input: PipelineInput, ctx: Context) -> FinalizeResult:
     ctx.log("finalize: saving transcript and setting status to 'ended'")
     logger.info("[Hatchet] finalize", transcript_id=input.transcript_id)
 
-    mixdown_data = _to_dict(ctx.task_output(mixdown_tracks))
-    track_data = _to_dict(ctx.task_output(process_tracks))
+    mixdown_data = to_dict(ctx.task_output(mixdown_tracks))
+    track_data = to_dict(ctx.task_output(process_tracks))
 
     duration = mixdown_data.get("duration", 0)
     all_words = track_data.get("all_words", [])

server/reflector/hatchet/workflows/track_processing.py

@@ -14,34 +14,25 @@ Hatchet workers run in forked processes; fresh imports per task ensure
 storage/DB connections are not shared across forks.
 """
 
-import math
 import tempfile
 from datetime import timedelta
-from fractions import Fraction
 from pathlib import Path
 
 import av
-from av.audio.resampler import AudioResampler
 from hatchet_sdk import Context
 from pydantic import BaseModel
 
 from reflector.hatchet.client import HatchetClientManager
+from reflector.hatchet.utils import to_dict
 from reflector.hatchet.workflows.models import PadTrackResult, TranscribeTrackResult
 from reflector.logger import logger
-from reflector.utils.audio_constants import (
-    OPUS_DEFAULT_BIT_RATE,
-    OPUS_STANDARD_SAMPLE_RATE,
-    PRESIGNED_URL_EXPIRATION_SECONDS,
+from reflector.utils.audio_constants import PRESIGNED_URL_EXPIRATION_SECONDS
+from reflector.utils.audio_padding import (
+    apply_audio_padding_to_file,
+    extract_stream_start_time_from_container,
 )
 
 
-def _to_dict(output) -> dict:
-    """Convert task output to dict, handling both dict and Pydantic model returns."""
-    if isinstance(output, dict):
-        return output
-    return output.model_dump()
-
-
 class TrackInput(BaseModel):
     """Input for individual track processing."""
 
@@ -58,124 +49,6 @@ hatchet = HatchetClientManager.get_client()
 track_workflow = hatchet.workflow(name="TrackProcessing", input_validator=TrackInput)
 
 
-def _extract_stream_start_time_from_container(container, track_idx: int) -> float:
-    """Extract meeting-relative start time from WebM stream metadata.
-
-    Uses PyAV to read stream.start_time from WebM container.
-    More accurate than filename timestamps by ~209ms due to network/encoding delays.
-    """
-    start_time_seconds = 0.0
-    try:
-        audio_streams = [s for s in container.streams if s.type == "audio"]
-        stream = audio_streams[0] if audio_streams else container.streams[0]
-
-        # 1) Try stream-level start_time (most reliable for Daily.co tracks)
-        if stream.start_time is not None and stream.time_base is not None:
-            start_time_seconds = float(stream.start_time * stream.time_base)
-
-        # 2) Fallback to container-level start_time
-        if (start_time_seconds <= 0) and (container.start_time is not None):
-            start_time_seconds = float(container.start_time * av.time_base)
-
-        # 3) Fallback to first packet DTS
-        if start_time_seconds <= 0:
-            for packet in container.demux(stream):
-                if packet.dts is not None:
-                    start_time_seconds = float(packet.dts * stream.time_base)
-                    break
-    except Exception as e:
-        logger.warning(
-            "PyAV metadata read failed; assuming 0 start_time",
-            track_idx=track_idx,
-            error=str(e),
-        )
-        start_time_seconds = 0.0
-
-    logger.info(
-        f"Track {track_idx} stream metadata: start_time={start_time_seconds:.3f}s",
-        track_idx=track_idx,
-    )
-    return start_time_seconds
-
-
-def _apply_audio_padding_to_file(
-    in_container,
-    output_path: str,
-    start_time_seconds: float,
-    track_idx: int,
-) -> None:
-    """Apply silence padding to audio track using PyAV filter graph."""
-    delay_ms = math.floor(start_time_seconds * 1000)
-
-    logger.info(
-        f"Padding track {track_idx} with {delay_ms}ms delay using PyAV",
-        track_idx=track_idx,
-        delay_ms=delay_ms,
-    )
-
-    with av.open(output_path, "w", format="webm") as out_container:
-        in_stream = next((s for s in in_container.streams if s.type == "audio"), None)
-        if in_stream is None:
-            raise Exception("No audio stream in input")
-
-        out_stream = out_container.add_stream("libopus", rate=OPUS_STANDARD_SAMPLE_RATE)
-        out_stream.bit_rate = OPUS_DEFAULT_BIT_RATE
-        graph = av.filter.Graph()
-
-        abuf_args = (
-            f"time_base=1/{OPUS_STANDARD_SAMPLE_RATE}:"
-            f"sample_rate={OPUS_STANDARD_SAMPLE_RATE}:"
-            f"sample_fmt=s16:"
-            f"channel_layout=stereo"
-        )
-        src = graph.add("abuffer", args=abuf_args, name="src")
-        aresample_f = graph.add("aresample", args="async=1", name="ares")
-        delays_arg = f"{delay_ms}|{delay_ms}"
-        adelay_f = graph.add("adelay", args=f"delays={delays_arg}:all=1", name="delay")
-        sink = graph.add("abuffersink", name="sink")
-
-        src.link_to(aresample_f)
-        aresample_f.link_to(adelay_f)
-        adelay_f.link_to(sink)
-        graph.configure()
-
-        resampler = AudioResampler(
-            format="s16", layout="stereo", rate=OPUS_STANDARD_SAMPLE_RATE
-        )
-
-        for frame in in_container.decode(in_stream):
-            out_frames = resampler.resample(frame) or []
-            for rframe in out_frames:
-                rframe.sample_rate = OPUS_STANDARD_SAMPLE_RATE
-                rframe.time_base = Fraction(1, OPUS_STANDARD_SAMPLE_RATE)
-                src.push(rframe)
-
-                while True:
-                    try:
-                        f_out = sink.pull()
-                    except Exception:
-                        break
-                    f_out.sample_rate = OPUS_STANDARD_SAMPLE_RATE
-                    f_out.time_base = Fraction(1, OPUS_STANDARD_SAMPLE_RATE)
-                    for packet in out_stream.encode(f_out):
-                        out_container.mux(packet)
-
-        # Flush remaining frames
-        src.push(None)
-        while True:
-            try:
-                f_out = sink.pull()
-            except Exception:
-                break
-            f_out.sample_rate = OPUS_STANDARD_SAMPLE_RATE
-            f_out.time_base = Fraction(1, OPUS_STANDARD_SAMPLE_RATE)
-            for packet in out_stream.encode(f_out):
-                out_container.mux(packet)
-
-        for packet in out_stream.encode(None):
-            out_container.mux(packet)
-
-
 @track_workflow.task(execution_timeout=timedelta(seconds=300), retries=3)
 async def pad_track(input: TrackInput, ctx: Context) -> PadTrackResult:
     """Pad single audio track with silence for alignment.
@@ -213,8 +86,8 @@ async def pad_track(input: TrackInput, ctx: Context) -> PadTrackResult:
 
         # Open container and extract start time
         with av.open(source_url) as in_container:
-            start_time_seconds = _extract_stream_start_time_from_container(
-                in_container, input.track_index
+            start_time_seconds = extract_stream_start_time_from_container(
+                in_container, input.track_index, logger=logger
             )
 
             # If no padding needed, return original S3 key
@@ -235,8 +108,12 @@ async def pad_track(input: TrackInput, ctx: Context) -> PadTrackResult:
                 temp_path = temp_file.name
 
             try:
-                _apply_audio_padding_to_file(
-                    in_container, temp_path, start_time_seconds, input.track_index
+                apply_audio_padding_to_file(
+                    in_container,
+                    temp_path,
+                    start_time_seconds,
+                    input.track_index,
+                    logger=logger,
                 )
 
                 file_size = Path(temp_path).stat().st_size
@@ -293,7 +170,7 @@ async def transcribe_track(input: TrackInput, ctx: Context) -> TranscribeTrackRe
     )
 
     try:
-        pad_result = _to_dict(ctx.task_output(pad_track))
+        pad_result = to_dict(ctx.task_output(pad_track))
         padded_key = pad_result.get("padded_key")
         bucket_name = pad_result.get("bucket_name")
 

server/reflector/pipelines/main_multitrack_pipeline.py

@@ -1,11 +1,8 @@
 import asyncio
-import math
 import tempfile
-from fractions import Fraction
 from pathlib import Path
 
 import av
-from av.audio.resampler import AudioResampler
 from celery import chain, shared_task
 
 from reflector.asynctask import asynctask
@@ -32,10 +29,14 @@ from reflector.processors.audio_waveform_processor import AudioWaveformProcessor
 from reflector.processors.types import TitleSummary
 from reflector.processors.types import Transcript as TranscriptType
 from reflector.storage import Storage, get_transcripts_storage
-from reflector.utils.audio_constants import (
-    OPUS_DEFAULT_BIT_RATE,
-    OPUS_STANDARD_SAMPLE_RATE,
-    PRESIGNED_URL_EXPIRATION_SECONDS,
+from reflector.utils.audio_constants import PRESIGNED_URL_EXPIRATION_SECONDS
+from reflector.utils.audio_mixdown import (
+    detect_sample_rate_from_tracks,
+    mixdown_tracks_pyav,
+)
+from reflector.utils.audio_padding import (
+    apply_audio_padding_to_file,
+    extract_stream_start_time_from_container,
 )
 from reflector.utils.daily import (
     filter_cam_audio_tracks,
@@ -123,8 +124,8 @@ class PipelineMainMultitrack(PipelineMainBase):
         try:
             # PyAV streams input from S3 URL efficiently (2-5MB fixed overhead for codec/filters)
             with av.open(track_url) as in_container:
-                start_time_seconds = self._extract_stream_start_time_from_container(
-                    in_container, track_idx
+                start_time_seconds = extract_stream_start_time_from_container(
+                    in_container, track_idx, logger=self.logger
                 )
 
                 if start_time_seconds <= 0:
@@ -142,8 +143,12 @@ class PipelineMainMultitrack(PipelineMainBase):
                     temp_path = temp_file.name
 
                 try:
-                    self._apply_audio_padding_to_file(
-                        in_container, temp_path, start_time_seconds, track_idx
+                    apply_audio_padding_to_file(
+                        in_container,
+                        temp_path,
+                        start_time_seconds,
+                        track_idx,
+                        logger=self.logger,
                     )
 
                     storage_path = (
@@ -184,317 +189,30 @@ class PipelineMainMultitrack(PipelineMainBase):
                 f"Track {track_idx} padding failed - transcript would have incorrect timestamps"
             ) from e
 
-    def _extract_stream_start_time_from_container(
-        self, container, track_idx: int
-    ) -> float:
-        """
-        Extract meeting-relative start time from WebM stream metadata.
-        Uses PyAV to read stream.start_time from WebM container.
-        More accurate than filename timestamps by ~209ms due to network/encoding delays.
-        """
-        start_time_seconds = 0.0
-        try:
-            audio_streams = [s for s in container.streams if s.type == "audio"]
-            stream = audio_streams[0] if audio_streams else container.streams[0]
-
-            # 1) Try stream-level start_time (most reliable for Daily.co tracks)
-            if stream.start_time is not None and stream.time_base is not None:
-                start_time_seconds = float(stream.start_time * stream.time_base)
-
-            # 2) Fallback to container-level start_time (in av.time_base units)
-            if (start_time_seconds <= 0) and (container.start_time is not None):
-                start_time_seconds = float(container.start_time * av.time_base)
-
-            # 3) Fallback to first packet DTS in stream.time_base
-            if start_time_seconds <= 0:
-                for packet in container.demux(stream):
-                    if packet.dts is not None:
-                        start_time_seconds = float(packet.dts * stream.time_base)
-                        break
-        except Exception as e:
-            self.logger.warning(
-                "PyAV metadata read failed; assuming 0 start_time",
-                track_idx=track_idx,
-                error=str(e),
-            )
-            start_time_seconds = 0.0
-
-        self.logger.info(
-            f"Track {track_idx} stream metadata: start_time={start_time_seconds:.3f}s",
-            track_idx=track_idx,
-        )
-        return start_time_seconds
-
-    def _apply_audio_padding_to_file(
-        self,
-        in_container,
-        output_path: str,
-        start_time_seconds: float,
-        track_idx: int,
-    ) -> None:
-        """Apply silence padding to audio track using PyAV filter graph, writing to file"""
-        delay_ms = math.floor(start_time_seconds * 1000)
-
-        self.logger.info(
-            f"Padding track {track_idx} with {delay_ms}ms delay using PyAV",
-            track_idx=track_idx,
-            delay_ms=delay_ms,
-        )
-
-        try:
-            with av.open(output_path, "w", format="webm") as out_container:
-                in_stream = next(
-                    (s for s in in_container.streams if s.type == "audio"), None
-                )
-                if in_stream is None:
-                    raise Exception("No audio stream in input")
-
-                out_stream = out_container.add_stream(
-                    "libopus", rate=OPUS_STANDARD_SAMPLE_RATE
-                )
-                out_stream.bit_rate = OPUS_DEFAULT_BIT_RATE
-                graph = av.filter.Graph()
-
-                abuf_args = (
-                    f"time_base=1/{OPUS_STANDARD_SAMPLE_RATE}:"
-                    f"sample_rate={OPUS_STANDARD_SAMPLE_RATE}:"
-                    f"sample_fmt=s16:"
-                    f"channel_layout=stereo"
-                )
-                src = graph.add("abuffer", args=abuf_args, name="src")
-                aresample_f = graph.add("aresample", args="async=1", name="ares")
-                # adelay requires one delay value per channel separated by '|'
-                delays_arg = f"{delay_ms}|{delay_ms}"
-                adelay_f = graph.add(
-                    "adelay", args=f"delays={delays_arg}:all=1", name="delay"
-                )
-                sink = graph.add("abuffersink", name="sink")
-
-                src.link_to(aresample_f)
-                aresample_f.link_to(adelay_f)
-                adelay_f.link_to(sink)
-                graph.configure()
-
-                resampler = AudioResampler(
-                    format="s16", layout="stereo", rate=OPUS_STANDARD_SAMPLE_RATE
-                )
-                # Decode -> resample -> push through graph -> encode Opus
-                for frame in in_container.decode(in_stream):
-                    out_frames = resampler.resample(frame) or []
-                    for rframe in out_frames:
-                        rframe.sample_rate = OPUS_STANDARD_SAMPLE_RATE
-                        rframe.time_base = Fraction(1, OPUS_STANDARD_SAMPLE_RATE)
-                        src.push(rframe)
-
-                        while True:
-                            try:
-                                f_out = sink.pull()
-                            except Exception:
-                                break
-                            f_out.sample_rate = OPUS_STANDARD_SAMPLE_RATE
-                            f_out.time_base = Fraction(1, OPUS_STANDARD_SAMPLE_RATE)
-                            for packet in out_stream.encode(f_out):
-                                out_container.mux(packet)
-
-                src.push(None)
-                while True:
-                    try:
-                        f_out = sink.pull()
-                    except Exception:
-                        break
-                    f_out.sample_rate = OPUS_STANDARD_SAMPLE_RATE
-                    f_out.time_base = Fraction(1, OPUS_STANDARD_SAMPLE_RATE)
-                    for packet in out_stream.encode(f_out):
-                        out_container.mux(packet)
-
-                for packet in out_stream.encode(None):
-                    out_container.mux(packet)
-        except Exception as e:
-            self.logger.error(
-                "PyAV padding failed for track",
-                track_idx=track_idx,
-                delay_ms=delay_ms,
-                error=str(e),
-                exc_info=True,
-            )
-            raise
-
     async def mixdown_tracks(
         self,
         track_urls: list[str],
         writer: AudioFileWriterProcessor,
         offsets_seconds: list[float] | None = None,
     ) -> None:
-        """Multi-track mixdown using PyAV filter graph (amix), reading from S3 presigned URLs"""
-
-        target_sample_rate: int | None = None
-        for url in track_urls:
-            if not url:
-                continue
-            container = None
-            try:
-                container = av.open(url)
-                for frame in container.decode(audio=0):
-                    target_sample_rate = frame.sample_rate
-                    break
-            except Exception:
-                continue
-            finally:
-                if container is not None:
-                    container.close()
-            if target_sample_rate:
-                break
-
+        """Multi-track mixdown using PyAV filter graph (amix), reading from S3 presigned URLs."""
+        # Detect sample rate from tracks
+        target_sample_rate = detect_sample_rate_from_tracks(
+            track_urls, logger=self.logger
+        )
         if not target_sample_rate:
             self.logger.error("Mixdown failed - no decodable audio frames found")
             raise Exception("Mixdown failed: No decodable audio frames in any track")
-        # Build PyAV filter graph:
-        # N abuffer (s32/stereo)
-        #   -> optional adelay per input (for alignment)
-        #   -> amix (s32)
-        #   -> aformat(s16)
-        #   -> sink
-        graph = av.filter.Graph()
-        inputs = []
-        valid_track_urls = [url for url in track_urls if url]
-        input_offsets_seconds = None
-        if offsets_seconds is not None:
-            input_offsets_seconds = [
-                offsets_seconds[i] for i, url in enumerate(track_urls) if url
-            ]
-        for idx, url in enumerate(valid_track_urls):
-            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)
 
-        if not inputs:
-            self.logger.error("Mixdown failed - no valid inputs for graph")
-            raise Exception("Mixdown failed: No valid inputs for filter graph")
-
-        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",
+        # Run mixdown using shared utility
+        await mixdown_tracks_pyav(
+            track_urls,
+            writer,
+            target_sample_rate,
+            offsets_seconds=offsets_seconds,
+            logger=self.logger,
         )
 
-        sink = graph.add("abuffersink", name="out")
-
-        # Optional per-input delay before mixing
-        delays_ms: list[int] = []
-        if input_offsets_seconds is not None:
-            base = min(input_offsets_seconds) if input_offsets_seconds else 0.0
-            delays_ms = [
-                max(0, int(round((o - base) * 1000))) for o in input_offsets_seconds
-            ]
-        else:
-            delays_ms = [0 for _ in inputs]
-
-        for idx, in_ctx in enumerate(inputs):
-            delay_ms = delays_ms[idx] if idx < len(delays_ms) else 0
-            if delay_ms > 0:
-                # adelay requires one value per channel; use same for stereo
-                adelay = graph.add(
-                    "adelay",
-                    args=f"delays={delay_ms}|{delay_ms}:all=1",
-                    name=f"delay{idx}",
-                )
-                in_ctx.link_to(adelay)
-                adelay.link_to(mixer, 0, idx)
-            else:
-                in_ctx.link_to(mixer, 0, idx)
-        mixer.link_to(fmt)
-        fmt.link_to(sink)
-        graph.configure()
-
-        containers = []
-        try:
-            # Open all containers with cleanup guaranteed
-            for i, url in enumerate(valid_track_urls):
-                try:
-                    c = av.open(
-                        url,
-                        options={
-                            # it's trying to stream from s3 by default
-                            "reconnect": "1",
-                            "reconnect_streamed": "1",
-                            "reconnect_delay_max": "5",
-                        },
-                    )
-                    containers.append(c)
-                except Exception as e:
-                    self.logger.warning(
-                        "Mixdown: failed to open container from URL",
-                        input=i,
-                        url=url,
-                        error=str(e),
-                    )
-
-            if not containers:
-                self.logger.error("Mixdown failed - no valid containers opened")
-                raise Exception("Mixdown failed: Could not open any track containers")
-
-            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
-            ]
-
-            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
-                        # causes stream to move on / unclogs memory
-                        inputs[i].push(None)
-                        continue
-
-                    if frame.sample_rate != target_sample_rate:
-                        continue
-                    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)
-
-                    while True:
-                        try:
-                            mixed = sink.pull()
-                        except Exception:
-                            break
-                        mixed.sample_rate = target_sample_rate
-                        mixed.time_base = Fraction(1, target_sample_rate)
-                        await writer.push(mixed)
-
-            while True:
-                try:
-                    mixed = sink.pull()
-                except Exception:
-                    break
-                mixed.sample_rate = target_sample_rate
-                mixed.time_base = Fraction(1, target_sample_rate)
-                await writer.push(mixed)
-        finally:
-            # Cleanup all containers, even if processing failed
-            for c in containers:
-                if c is not None:
-                    try:
-                        c.close()
-                    except Exception:
-                        pass  # Best effort cleanup
-
     @broadcast_to_sockets
     async def set_status(self, transcript_id: str, status: TranscriptStatus):
         async with self.lock_transaction():