Converts .vtt to .srt subtitles with python3

vtt2srt

#!/usr/bin/env python
# put this file in /usr/local/bin
# vtt2srt my_subtitle.vtt
import os, re, argparse

parser = argparse.ArgumentParser()
parser.add_argument("filename", help=".vtt file")
args = parser.parse_args()
input_path_filename = args.filename

assert input_path_filename.endswith(".vtt"), "input file should be .vtt"
output_path_filename = input_path_filename[:-4] + ".srt"


time_pattern = r"\b\d{2}:\d{2}:\d{2}\.\d{3}\b --> \b\d{2}:\d{2}:\d{2}\.\d{3}\b"
tag_pattern = r"<.+?>"
count_time = 0
subtitles = False

print("processing… " + input_path_filename)
with open(output_path_filename, "w") as output:
    with open(input_path_filename, "r") as input:
        for line in input:

            pattern = re.search(time_pattern, line)

            if subtitles and not pattern:
                subtitle_line = line.strip()
                subtitle_line = re.sub(tag_pattern, "", subtitle_line)
                output.write(subtitle_line + os.linesep)

            if pattern:
                count_time += 1
                time_string = pattern.group()
                output.write(str(count_time) + os.linesep)
                output.write(time_string.replace(".", ",") + os.linesep)
                subtitles = True
print("done        " + output_path_filename)