1 files changed, 117 insertions, 0 deletions
diff --git a/converter/audio.py b/converter/audio.py
new file mode 100644
index 0000000..ab55e9b
--- /dev/null
+++ b/converter/audio.py
@@ -0,0 +1,117 @@
+"""Audio assembly: combining chunks, speed adjustment, cleanup."""
+
+import logging
+import traceback
+from pathlib import Path
+from typing import Dict, List, Optional
+
+from . import config
+
+logger = logging.getLogger(__name__)
+
+
+def speed_export_params(speed: float) -> List[str]:
+    """Return ffmpeg filter args for pitch-preserving speed adjustment.
+
+    Uses ffmpeg's atempo filter, which accepts 0.5..2.0 per filter. Values
+    outside that range are handled by chaining multiple atempo filters.
+    """
+    if speed <= 0:
+        raise ValueError(f"Speed must be a positive number, got {speed}")
+    if abs(speed - 1.0) < 1e-6:
+        return []
+    remaining = float(speed)
+    chain = []
+    while remaining > 2.0:
+        chain.append("atempo=2.0")
+        remaining /= 2.0
+    while remaining < 0.5:
+        chain.append("atempo=0.5")
+        remaining /= 0.5
+    chain.append(f"atempo={remaining:g}")
+    return ["-filter:a", ",".join(chain)]
+
+
+def combine_chunks(total_chunks: int, output_path: Path,
+                   results: Optional[Dict[int, bool]] = None, speed: float = 1.0) -> bool:
+    """Combine audio chunks into the final audiobook.
+
+    ``results`` maps chunk numbers to success flags; failed chunks are
+    skipped. When ``speed`` differs from 1.0, an additional speed-adjusted
+    copy is written next to the normal-speed file.
+    """
+    try:
+        from pydub import AudioSegment
+    except ImportError:
+        logger.error("pydub is required to combine audio chunks (pip install pydub)")
+        return False
+
+    try:
+        combined = AudioSegment.empty()
+        successful = 0
+        missing_chunks = []
+
+        for i in range(1, total_chunks + 1):
+            # Skip chunks that failed if we have results tracking
+            if results is not None and not results.get(i, False):
+                missing_chunks.append(i)
+                continue
+
+            chunk_file = config.CHUNKS_FOLDER / f"chunk_{i:04d}.wav"
+            if chunk_file.exists():
+                try:
+                    combined += AudioSegment.from_wav(str(chunk_file))
+                    successful += 1
+                    if successful % 10 == 0:
+                        logger.info("Combined %d chunks", successful)
+                except Exception as exc:
+                    logger.warning("Failed to load chunk %d: %s", i, exc)
+                    missing_chunks.append(i)
+            else:
+                logger.warning("Chunk file not found: %s", chunk_file)
+                missing_chunks.append(i)
+
+        if successful == 0:
+            raise RuntimeError("No valid chunks found")
+
+        if missing_chunks:
+            logger.warning("Missing chunks: %s", missing_chunks)
+
+        combined.export(str(output_path), format=config.AUDIO_FORMAT, bitrate=config.AUDIO_BITRATE)
+        logger.info("Audiobook saved: %s (%d/%d chunks)", output_path, successful, total_chunks)
+        print(f"[INFO] Saved audiobook: {output_path.name} ({successful}/{total_chunks} chunks)")
+
+        export_params = speed_export_params(speed)
+        if export_params:
+            speed_path = output_path.with_name(f"{output_path.stem}_{speed:g}{output_path.suffix}")
+            combined.export(str(speed_path), format=config.AUDIO_FORMAT,
+                            bitrate=config.AUDIO_BITRATE, parameters=export_params)
+            logger.info("Saved speed-adjusted audiobook (%gx): %s", speed, speed_path)
+            print(f"[INFO] Saved speed-adjusted audiobook: {speed_path.name} ({speed:g}x)")
+
+        if missing_chunks:
+            print(f"[WARNING] Missing chunks: {missing_chunks}")
+        return True
+
+    except Exception as exc:
+        logger.error("Failed to combine chunks: %s", exc)
+        logger.error(traceback.format_exc())
+        return False
+
+
+def cleanup_chunks() -> None:
+    """Remove temporary chunk files from the scratch folder."""
+    try:
+        chunk_count = 0
+        for chunk_file in config.CHUNKS_FOLDER.glob("chunk_*.wav"):
+            try:
+                chunk_file.unlink()
+                chunk_count += 1
+            except Exception as exc:
+                logger.warning("Failed to delete %s: %s", chunk_file, exc)
+
+        if chunk_count > 0:
+            logger.info("Cleaned up %d chunk files", chunk_count)
+            print(f"[INFO] Cleaned up {chunk_count} chunk files")
+    except Exception as exc:
+        logger.warning("Cleanup failed: %s", exc)