loudnorm script

import subprocess
import json
import re
import os

def run_first_pass(input_file):
    command = [
        'ffmpeg',
        '-i', input_file,
        '-vn',
        '-filter_complex',
        'loudnorm=I=-14:TP=-2:LRA=11:print_format=json',
        '-f', 'null', '-'
    ]
    result = subprocess.run(command, stdout=subprocess.PIPE, stderr=subprocess.PIPE, text=True, encoding='utf-8', errors='replace')

    match = re.search(r'\{[\s\S]*?\}', result.stderr)
    if not match:
        raise RuntimeError("Could not find loudnorm JSON output.")

    loudnorm_data = json.loads(match.group(0))
    print("parsed data:")
    print(loudnorm_data)
    return loudnorm_data

def run_second_pass(input_file, output_file, loudnorm_data):
    loudnorm_filter = (
        f"loudnorm=I=-14:TP=-2:LRA=11:measured_I={loudnorm_data['input_i']}:"
        f"measured_TP={loudnorm_data['input_tp']}:measured_LRA={loudnorm_data['input_lra']}:"
        f"measured_thresh={loudnorm_data['input_thresh']}:offset={loudnorm_data['target_offset']}:linear=true:print_format=summary"
    )

    filter_complex = f"{loudnorm_filter}"


    command = [
        'ffmpeg',
        '-i', input_file,
        '-filter_complex', filter_complex,
        '-vn',
        '-c:a', 'aac',
        '-b:a', '320k',
        output_file
    ]

    subprocess.run(command, check=True)
    print("Done.")

def process_audio(input_file, output_file):
    print("Running first pass...")
    loudnorm_data = run_first_pass(input_file)

    print("Running second pass...")
    run_second_pass(input_file, output_file, loudnorm_data)

def main():
    list_file = "to_loudnorm.txt"
    out_dir = "out"
    with open(list_file, 'r', encoding='utf-8-sig') as f:
        for line in f:
            input_path = line.strip()
            if not input_path:
                continue

            output_path = os.path.join(out_dir, os.path.splitext(input_path)[0] + ".m4a")
            output_dir = os.path.dirname(output_path)

            try:
                process_audio(input_path, output_path)
            except Exception as e:
                print(f"Failed to process {input_path}: {e}")

if __name__ == "__main__":
    main()