Python script to adjust srt/subtitles files

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It's quite common to have synchronization problems with subtitles files. Indeed, very often the subtitle file is not adapted to our source video file. So we usually have a delay that goes from a few milliseconds to a few seconds which can be quite annoying when playing.

It's possible, with most players (vlc, mpv or mplayer); see here; to adjust the delay, but the configuration will be lost at the next playback. So it is more interesting to be able to adjust by directly modifying the subtitle file.

I already developed a script in bash to do just that, but I wanted to do it in Python so here it is.


  • Usage :
user@host:~$ ./ [srt file] [+/- time]
user@host:~$ ./ -h
usage: /movies/ -1.400

add/subtract delay on a srt file

positional arguments:
  file        srt file path
  delay       delay in seconds with 0.000 format

optional arguments:
  -h, --help  show this help message and exit
  • Subtract 400 miliseconds to subtitles :
user@host:~$ ./ /home/std/ -0.400
  • Add 1.400 seconds to subtitles :
user@host:~$ ./ /home/std/ 1.400
Note : The new srt file will be wrote in the same folder than source srt file with "" suffix.

srt file format

  • This script has been built to work with this kind or srt files only :
01:55:12,527 --> 01:55:14,461
I love you.

01:55:20,735 --> 01:55:22,669
I really love you.


#! /usr/bin/python

# Role : Add or subtract delay to a srt file
# Author :
# 1.0 first version

import argparse
import re, sys
from datetime import datetime, timedelta
import shutil
from tempfile import mkstemp
from os import path

parser = argparse.ArgumentParser(description='add/subtract delay on a srt file',prog='', usage='%(prog)s /movies/ -1.400')
parser.add_argument('file', help='srt file path')
parser.add_argument('delay', help='delay in seconds with 0.000 format')
args = parser.parse_args()

def timeop (hours, minutes, seconds, milliseconds, delay):
        "function which add or subtract delayed time then return result"
        time_src = datetime(year=1983, month=12, day=12, hour=int(hours), minute=int(minutes), second=int(seconds), microsecond=int(milliseconds)).timestamp()
        result = time_src + delay
        return result

        delay = float(args.delay)
        print("Error, float argument needed.")

if not path.exists(args.file):
        print("Error, file doesn't exist.")

fs = open(args.file, 'r') #open srt file, read mode
fd, name = mkstemp() #returns a tuple containing an OS-level handle to an open file and the absolute pathname of that file, in that order.
fout = open(name, 'w') #open temp file, write mode
while 1:
        txt = fs.readline()
        if re.match(".*-->.*", txt): #if ".*-->.*" characters is in current line
                seq=txt.split(" --> ")
                hours_start, minutes_start, seconds_start = seq[0].split(":")
                hours_start = hours_start[-1:]
                seconds_start, milliseconds_start = seconds_start.split(",")
                milliseconds_start = int(milliseconds_start) * 1000
                new_start = timeop(hours_start, minutes_start, seconds_start, milliseconds_start, delay)

                hours_end, minutes_end, seconds_end = seq[1].split(":")
                hours_end = hours_end[-1:]
                seconds_end, milliseconds_end = seconds_end.split(",")
                milliseconds_end = int(milliseconds_end) * 1000
                new_end = timeop(hours_end, minutes_end, seconds_end, milliseconds_end, delay)

                txt = re.sub(seq[0], datetime.fromtimestamp(new_start).strftime('%H:%M:%S,%f')[:-3], txt)
                txt = re.sub(seq[1], datetime.fromtimestamp(new_end).strftime('%H:%M:%S,%f')[:-3], txt) + "\n"
                fout.write(txt) #write to tmp file
                fout.write(txt) #write to tmp file

        if txt == "":
fout.close() #close tmp file
shutil.move(name, args.file.split(".srt")[0] + "") #copy tmp file to
fs.close() #close srt file
Creative Commons License
This work is licensed under a Creative Commons Attribution-NonCommercial-ShareAlike 4.0 International License.

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