Fix truncated Opus tail in streaming writer

README.md

@@ -256,6 +256,8 @@ response = requests.post(
 - m4a
 - pcm
 
+Implementation note: Opus output is encoded on a 48 kHz codec clock. When streaming to an in-memory buffer, the final Ogg/Opus pages are only available after the muxer is closed, so the last response chunk must be read after finalization to avoid truncating the tail of the clip.
+
 <p align="center">
 <img src="assets/format_comparison.png" width="80%" alt="Audio Format Comparison" style="border: 2px solid #333; padding: 10px;">
 </p>

api/src/services/streaming_audio_writer.py

@@ -1,14 +1,11 @@
 """Audio conversion service with proper streaming support"""
 
-import struct
 from io import BytesIO
 from typing import Optional
 
 import av
 import numpy as np
-import soundfile as sf
 from loguru import logger
-from pydub import AudioSegment
 
 
 class StreamingAudioWriter:
@@ -20,6 +17,8 @@ def __init__(self, format: str, sample_rate: int, channels: int = 1):
         self.channels = channels
         self.bytes_written = 0
         self.pts = 0
+        # Opus is muxed on a 48 kHz clock even when the source PCM is 24 kHz.
+        self.codec_sample_rate = 48000 if self.format == "opus" else self.sample_rate
 
         codec_map = {
             "wav": "pcm_s16le",
@@ -47,21 +46,31 @@ def __init__(self, format: str, sample_rate: int, channels: int = 1):
                 )
                 self.stream = self.container.add_stream(
                     codec_map[self.format],
-                    rate=self.sample_rate,
+                    rate=self.codec_sample_rate,
                     layout="mono" if self.channels == 1 else "stereo",
                 )
                 # Set bit_rate only for codecs where it's applicable and useful
                 if self.format in ['mp3', 'aac', 'opus']:
                     self.stream.bit_rate = 128000
+
+                if self.format == "opus":
+                    # Resample the model's 24 kHz PCM into the codec clock expected by Opus.
+                    self.resampler = av.AudioResampler(
+                        format="s16",
+                        layout="mono" if self.channels == 1 else "stereo",
+                        rate=self.codec_sample_rate,
+                    )
         else:
             raise ValueError(f"Unsupported format: {self.format}") # Use self.format here
 
     def close(self):
         if hasattr(self, "container"):
             self.container.close()
+            del self.container
 
         if hasattr(self, "output_buffer"):
             self.output_buffer.close()
+            del self.output_buffer
 
     def write_chunk(
         self, audio_data: Optional[np.ndarray] = None, finalize: bool = False
@@ -84,9 +93,15 @@ def write_chunk(
                 # No explicit flush method is available or needed here.
                 logger.debug("Muxed final packets.")
 
+                # The Opus/Ogg muxer keeps the final pages in memory until close().
+                # Reading the buffer before close truncates the tail of the stream.
+                self.container.close()
+                del self.container
+
                 # Get the final bytes from the buffer *before* closing it
                 data = self.output_buffer.getvalue()
-                self.close() # Close container and buffer
+                self.output_buffer.close()
+                del self.output_buffer
                 return data
 
         if audio_data is None or len(audio_data) == 0:
@@ -103,12 +118,23 @@ def write_chunk(
             )
             frame.sample_rate = self.sample_rate
 
-            frame.pts = self.pts
-            self.pts += frame.samples
-
-            packets = self.stream.encode(frame)
-            for packet in packets:
-                self.container.mux(packet)
+            frames_to_encode = [frame]
+            if self.format == "opus":
+                resampled = self.resampler.resample(frame)
+                if resampled is None:
+                    frames_to_encode = []
+                elif isinstance(resampled, list):
+                    frames_to_encode = resampled
+                else:
+                    frames_to_encode = [resampled]
+
+            for encode_frame in frames_to_encode:
+                encode_frame.pts = self.pts
+                self.pts += encode_frame.samples
+
+                packets = self.stream.encode(encode_frame)
+                for packet in packets:
+                    self.container.mux(packet)
 
             data = self.output_buffer.getvalue()
             self.output_buffer.seek(0)

api/tests/test_audio_service.py

@@ -1,7 +1,9 @@
 """Tests for AudioService"""
 
+from io import BytesIO
 from unittest.mock import patch
 
+import av
 import numpy as np
 import pytest
 
@@ -80,16 +82,35 @@ async def test_convert_to_opus(sample_audio):
     writer = StreamingAudioWriter("opus", sample_rate=24000)
 
     audio_chunk = await AudioService.convert_audio(
-        AudioChunk(audio_data), "opus", writer
+        AudioChunk(audio_data), "opus", writer, is_last_chunk=False, trim_audio=False
+    )
+    final_chunk = await AudioService.convert_audio(
+        AudioChunk(np.array([], dtype=np.int16)),
+        "opus",
+        writer,
+        is_last_chunk=True,
+        trim_audio=False,
     )
 
-    writer.close()
+    encoded = audio_chunk.output + final_chunk.output
 
-    assert isinstance(audio_chunk.output, bytes)
+    assert isinstance(encoded, bytes)
     assert isinstance(audio_chunk, AudioChunk)
-    assert len(audio_chunk.output) > 0
+    assert len(encoded) > 0
     # Check OGG header
-    assert audio_chunk.output.startswith(b"OggS")
+    assert encoded.startswith(b"OggS")
+
+    with av.open(BytesIO(encoded), mode="r", format="ogg") as container:
+        decoded_samples = 0
+        decoded_rate = None
+        for frame in container.decode(audio=0):
+            decoded_samples += frame.samples
+            decoded_rate = frame.sample_rate
+
+    assert decoded_rate == 48000
+    assert decoded_samples / decoded_rate == pytest.approx(
+        len(audio_data) / sample_rate, abs=0.03
+    )
 
 
 @pytest.mark.asyncio