implemented 15,12,18 didn't check 18

backend/services/audio_cleaner.py

@@ -158,3 +158,125 @@ def detect_silence_ranges(input_path: str, min_silence_ms: int, silence_db: floa
         silence_db,
     )
     return ranges
+
+
+def normalize_audio(
+    input_path: str,
+    output_path: str = "",
+    target_lufs: float = -14.0,
+) -> str:
+    """
+    Normalize audio loudness to a target LUFS level using FFmpeg's loudnorm filter.
+
+    Args:
+        input_path: Path to the input audio/video file.
+        output_path: Path for the normalized output. Auto-generated if empty.
+        target_lufs: Target integrated loudness in LUFS.
+                     Common targets: -14 (YouTube), -16 (Spotify), -23 (broadcast).
+
+    Returns: path to the normalized audio file.
+    """
+    import os as _os
+
+    inp = Path(input_path)
+    if not output_path:
+        output_path = str(inp.with_stem(inp.stem + "_normalized"))
+
+    # Two-pass loudnorm: first pass measures loudness, second pass applies correction.
+    # First pass: measure only (print_format=json)
+    measure_cmd = [
+        "ffmpeg", "-y",
+        "-i", str(inp),
+        "-af", f"loudnorm=I={target_lufs}:LRA=7:TP=-1.5:print_format=json",
+        "-f", "null",
+        "-",
+    ]
+    logger.info("Running loudnorm first pass (measurement): %s", " ".join(measure_cmd))
+    measure_result = subprocess.run(measure_cmd, capture_output=True, text=True)
+
+    # Parse measured parameters from stderr (loudnorm outputs JSON to stderr)
+    measured = _parse_loudnorm_measurement(measure_result.stderr)
+    if not measured:
+        logger.warning(
+            "loudnorm measurement failed or produced no output; "
+            "falling back to single-pass normalization"
+        )
+        # Single-pass fallback
+        cmd = [
+            "ffmpeg", "-y",
+            "-i", str(inp),
+            "-af", f"loudnorm=I={target_lufs}:LRA=7:TP=-1.5",
+            "-c:v", "copy",
+            output_path,
+        ]
+        result = subprocess.run(cmd, capture_output=True, text=True)
+        if result.returncode != 0:
+            raise RuntimeError(f"Audio normalization failed: {result.stderr[-300:]}")
+        logger.info("Single-pass normalized audio saved to %s", output_path)
+        return output_path
+
+    # Second pass: apply normalization using measured values
+    input_i = measured.get("input_i", target_lufs)
+    input_lra = measured.get("input_lra", 7.0)
+    input_tp = measured.get("input_tp", -1.5)
+    input_thresh = measured.get("input_thresh", -30.0)
+    offset = measured.get("target_offset", 0.0)
+
+    apply_cmd = [
+        "ffmpeg", "-y",
+        "-i", str(inp),
+        "-af",
+        (
+            f"loudnorm=I={target_lufs}:LRA=7:TP=-1.5:"
+            f"measured_I={input_i}:measured_LRA={input_lra}:"
+            f"measured_TP={input_tp}:measured_thresh={input_thresh}:"
+            f"offset={offset}:linear=true:print_format=summary"
+        ),
+        "-c:v", "copy",
+        output_path,
+    ]
+    logger.info("Running loudnorm second pass (apply): %s", " ".join(apply_cmd))
+    result = subprocess.run(apply_cmd, capture_output=True, text=True)
+    if result.returncode != 0:
+        raise RuntimeError(f"Audio normalization (apply) failed: {result.stderr[-300:]}")
+
+    logger.info(
+        "Normalized audio saved to %s (target=%s LUFS, measured_I=%s)",
+        output_path,
+        target_lufs,
+        input_i,
+    )
+    return output_path
+
+
+def _parse_loudnorm_measurement(stderr_output: str) -> dict:
+    """Parse loudnorm JSON measurement output from FFmpeg stderr."""
+    import json
+
+    # loudnorm prints JSON block between "Parsed_loudnorm" lines
+    lines = stderr_output.split("\n")
+    json_lines = []
+    in_json = False
+    for line in lines:
+        if "Parsed_loudnorm" in line and "}" in line:
+            # Single-line JSON
+            try:
+                start = line.index("{")
+                end = line.rindex("}") + 1
+                return json.loads(line[start:end])
+            except (ValueError, json.JSONDecodeError):
+                continue
+        if "{" in line and not in_json:
+            in_json = True
+        if in_json:
+            json_lines.append(line)
+        if in_json and "}" in line:
+            in_json = False
+            break
+
+    if json_lines:
+        try:
+            return json.loads("".join(json_lines))
+        except json.JSONDecodeError:
+            pass
+    return {}