Offsets timestamps in an SRT file by given number of seconds.

subtitle_mover.py

#!/usr/bin/env python3

import sys
import re

USAGE = """
Usage: subtitle_mover.py [offset_seconds] < original.srt > processed.srt
"""

def move_timestamps(line, seconds_offset):
    new_line = line
    matches = re.findall("\\d\\d:\\d\\d:\\d\\d", line)
    for match in matches:
        vals = [int(x) for x in match.split(':')]
        seconds = vals[0] * 60 * 60 + vals[1] * 60 + vals[2]
        new_seconds = seconds + seconds_offset
        val1 = new_seconds // (60**2)
        new_seconds -= val1 * 60**2
        val2 = new_seconds // 60
        new_seconds -= val2 * 60
        val3 = new_seconds
        r = ["{}".format(x).rjust(2, '0') for x in [val1, val2, val3]]
        replacement = "{}:{}:{}".format(r[0], r[1], r[2])
        new_line = new_line.replace(match, replacement)
    return new_line

try:
    seconds_to_move = int(sys.argv[1])
except: 
    print(USAGE)
    sys.exit(-1)

for line in sys.stdin:
    print(move_timestamps(line.rstrip(), seconds_to_move))