Line Length Limiter in Python

import re
import codecs

def merge_subtitle_lines(input_file, output_file, max_characters):
    with codecs.open(input_file, 'r', encoding='utf-8-sig') as f:
        content = f.readlines()

    new_content = []
    buffer = []
    for line in content:
        if re.match(r'^\d+$', line.strip()):
            if buffer:
                merged_line = ' '.join(buffer)
                if len(merged_line) <= max_characters:
                    new_content.append(merged_line + '\n')
                else:
                    new_content.extend(buffer)
                    new_content.append('\n')
                buffer = []
            new_content.append(line)
        elif re.match(r'^\d{2}:\d{2}:\d{2},\d{3} --> \d{2}:\d{2}:\d{2},\d{3}$', line.strip()):
            new_content.append(line)
        elif line.strip():
            if not buffer:
                buffer.append(line.strip())
            elif len(' '.join(buffer + [line.strip()])) <= max_characters:
                buffer.append(line.strip())
            else:
                new_content.extend(buffer)
                new_content.append('\n')
                buffer = [line.strip()]
        else:
            if buffer:
                new_content.extend(buffer)
                new_content.append('\n')
            new_content.append(line)
            buffer = []

    if buffer:
        new_content.extend(buffer)
        new_content.append('\n')

    with open(output_file, 'w', encoding='utf-8') as f:
        f.writelines(new_content)

input_file = "E:/Desktop/testsub/16.Sub_ING.srt"
output_file = "E:/Desktop/testsub/out/16.Sub_ING1.srt"
max_characters = 56

merge_subtitle_lines(input_file, output_file, max_characters)