Shift SRT Subtitle Timing Using a Python Script

Last updated: Jul 27, 2025

Subtitle synchronization issues are quite common. In many cases, the subtitle file doesn't match the timing of the video source, resulting in a delay that can range from a few milliseconds to several seconds — which quickly becomes annoying during playback.

While most media players like VLC, MPV, or MPlayer allow you to manually adjust the subtitle delay (see this guide), the adjustment is temporary and will reset the next time you play the file. A more permanent solution is to directly modify the SRT subtitle file.

I had previously written a Bash script to handle this task, but I decided to rewrite it in Python for better flexibility and readability. Here’s how it works.

Usage

To shift the timing of subtitles in an SRT file, use the script as follows:

user@host:~$ ./shebangthesubtitles.py [srt file] [+/- time]

user@host:~$ ./shebangthesubtitles.py -h
usage: shebangthesubtitles.py /movies/mysubtitle.srt -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

Examples

Shift subtitles 400 milliseconds earlier:

user@host:~$ ./shebangthesubtitles.py /home/std/Running.on.Empty.1988.1080p.BluRay.x264.AAC.5.1-POOP.srt -0.400

Delay subtitles by 1.4 seconds:

user@host:~$ ./shebangthesubtitles.py /home/std/Running.on.Empty.1988.1080p.BluRay.x264.AAC.5.1-POOP.srt 1.400

Note: The adjusted subtitle file will be saved in the same directory as the original, with _new.srt appended to the filename.

SRT File Format

This script is designed to work specifically with standard .srt subtitle files that follow the typical format shown below:

[…]
1126
01:55:12,527 --> 01:55:14,461
I love you.

1127
01:55:20,735 --> 01:55:22,669
I really love you.

Python Script

This is the full Python script used to shift the timing of SRT subtitle files. You can add or subtract a delay (in seconds) by specifying a positive or negative value.

#! /usr/bin/python

# Role : Add or subtract delay to a srt file
# Author : http://shebangthedolphins.net/
# 1.0 first version

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

###START PARSER : https://docs.python.org/3/library/argparse.html
parser = argparse.ArgumentParser(description='add/subtract delay on a srt file',prog='shebangthesubtitles.py', usage='%(prog)s /movies/mysubtitle.srt -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()
###END PARSER

###FUNCTION
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

###CHECK ARGUMENTS
try:
        delay = float(args.delay)
except:
        print("Error, float argument needed.")
        parser.print_help()
        sys.exit(1)

if not path.exists(args.file):
        print("Error, file doesn't exist.")
        parser.print_help()
        sys.exit(1)


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
        else:
                fout.write(txt) #write to tmp file

        if txt == "":
                break
fout.close() #close tmp file
shutil.move(name, args.file.split(".srt")[0] + "_new.srt") #copy tmp file to srtfile_new.srt
fs.close() #close srt file

Download : shebangthesubtitles.py