Decode SNAC in single pass to fix audio artifacts

SNAC's convolutional decoder has a receptive field spanning multiple
frames. Batched decode (28 tokens at a time) created boundary
discontinuities that produced muddled audio. Since pw-play waits for
the full WAV anyway, single-pass decode costs only ~2s extra and
produces clean audio.

src/tts_mcp/engines/orpheus.py

@@ -24,8 +24,6 @@ SAMPLE_RATE = 24000
 SNAC_CODEBOOK_SIZE = 4096
 TOKEN_PATTERN = re.compile(r"<custom_token_(\d+)>")
 TOKENS_PER_FRAME = 7
-FRAMES_PER_BATCH = 4
-BATCH_SIZE = TOKENS_PER_FRAME * FRAMES_PER_BATCH  # 28
 
 ALL_VOICES = ["tara", "leah", "jess", "leo", "dan", "mia", "zac", "zoe"]
 
@@ -149,13 +147,15 @@ class OrpheusEngine(TTSEngine):
         loop = asyncio.get_running_loop()
         snac = await self._get_snac()
 
-        # Stream tokens from llama-server via SSE
+        # Stream tokens from llama-server via SSE, then decode in one pass.
+        # SNAC's convolutional decoder has a receptive field spanning multiple
+        # frames, so batched decode creates boundary artifacts. Since pw-play
+        # waits for the full WAV anyway, single-pass decode costs only ~2s
+        # extra on a 50s generation — and produces clean audio.
         t0 = time.time()
         token_strings: list[str] = []
-        audio_chunks: list[np.ndarray] = []
         total_tokens = 0
         dropped_lines = 0
-        stream_interrupted = False
 
         try:
             async with self._client.stream(
@@ -202,27 +202,16 @@ class OrpheusEngine(TTSEngine):
                         token_strings.append(f"<custom_token_{m}>")
                         total_tokens += 1
 
-                    # Batch decode every 28 tokens (4 SNAC frames)
-                    while len(token_strings) >= BATCH_SIZE:
-                        batch = token_strings[:BATCH_SIZE]
-                        token_strings = token_strings[BATCH_SIZE:]
-                        chunk_audio = await loop.run_in_executor(
-                            None, _tokens_to_audio, batch, snac
-                        )
-                        if chunk_audio is not None:
-                            audio_chunks.append(chunk_audio)
-
         except httpx.ConnectError as e:
             raise RuntimeError(f"Cannot reach llama-server at {self._url}: {e}") from e
         except (httpx.ReadError, httpx.RemoteProtocolError) as e:
-            if not audio_chunks:
+            if total_tokens < TOKENS_PER_FRAME:
                 raise RuntimeError(
-                    f"llama-server connection lost with no audio decoded: {e}"
+                    f"llama-server connection lost with no usable tokens: {e}"
                 ) from e
-            stream_interrupted = True
             print(
                 f"  Warning: llama-server connection lost after {total_tokens} tokens. "
-                f"Using {len(audio_chunks)} partial chunks.",
+                "Decoding what we have.",
                 file=sys.stderr,
             )
 
@@ -234,32 +223,29 @@ class OrpheusEngine(TTSEngine):
                 file=sys.stderr,
             )
 
-        # Flush remaining tokens (drop partial frame — at most 0.29ms lost)
-        if token_strings:
-            usable = len(token_strings) - (len(token_strings) % TOKENS_PER_FRAME)
-            if usable > 0:
-                chunk_audio = await loop.run_in_executor(
-                    None, _tokens_to_audio, token_strings[:usable], snac
-                )
-                if chunk_audio is not None:
-                    audio_chunks.append(chunk_audio)
+        # Drop partial frame at end (at most 6 tokens / 0.29ms lost)
+        usable = len(token_strings) - (len(token_strings) % TOKENS_PER_FRAME)
 
-        num_frames = total_tokens // TOKENS_PER_FRAME
+        num_frames = usable // TOKENS_PER_FRAME
         tok_per_sec = total_tokens / gen_time if gen_time > 0 else 0
-        status = " (TRUNCATED)" if stream_interrupted else ""
         print(
             f"  Orpheus: {total_tokens} tokens ({num_frames} frames) "
-            f"in {gen_time:.1f}s ({tok_per_sec:.1f} tok/s){status}",
+            f"in {gen_time:.1f}s ({tok_per_sec:.1f} tok/s)",
             file=sys.stderr,
         )
 
-        if not audio_chunks:
+        if usable < TOKENS_PER_FRAME:
             raise RuntimeError(
                 f"Orpheus returned insufficient tokens ({total_tokens}). "
                 "Check llama-server logs."
             )
 
-        audio = np.concatenate(audio_chunks)
+        # Single-pass SNAC decode — full context across all frames
+        audio = await loop.run_in_executor(
+            None, _tokens_to_audio, token_strings[:usable], snac
+        )
+        if audio is None:
+            raise RuntimeError("SNAC decoding produced no audio")
         path = write_wav(audio, SAMPLE_RATE, prefix="orpheus-")
 
         return TTSResult(