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diff --git a/srtshift.py b/srtshift.py
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+#!/usr/bin/python
+
+# Copyright (C) 2012 Jorge Gorbe Moya <jgorbe@slackito.com>
+#
+# This program is free software. It comes without any warranty, to
+# the extent permitted by applicable law. You can redistribute it
+# and/or modify it under the terms of the Do What The Fuck You Want
+# To Public License, Version 2, as published by Sam Hocevar. See
+# http://sam.zoy.org/wtfpl/COPYING for more details
+
+# Quick and dirty SRT subtitle timestamp shifting tool.
+#
+# usage: srtshift <infile> <outfile> <offset-in-seconds>
+
+import sys
+
+# possible exceptions
+class SubtitleFormatError:
+       pass
+
+# a SRT timestamp class, convertible to and from string, with a shifting(add) method
+class Timestamp:
+       def __init__(self, h, m, s, ms):
+               self.hours   = h
+               self.minutes = m
+               self.secs    = s
+               self.ms      = ms
+
+       def addSeconds(self, seconds):
+               offset_ms = int(seconds*1000)
+               # add offset to self.ms
+               ms = self.ms + offset_ms
+        # propagate to seconds
+               secs = self.secs + ms / 1000
+               ms = ms % 1000
+        #propagate to minutes
+               minutes = self.minutes + secs / 60
+               secs = secs % 60
+        #propagate to hours
+               hours = self.hours + minutes / 60
+               minutes = minutes % 60
+               # if result is negative, it will have been propagated to the hours component 
+               if hours < 0:
+                       return Timestamp(0,0,0,0)
+               else:
+                       return Timestamp(hours, minutes, secs, ms)
+
+
+       def __str__(self):
+               return "%02d:%02d:%02d,%03d"%(self.hours, self.minutes, self.secs, self.ms)
+
+       @classmethod
+       def fromString(cls, s):
+               items = s.split(":")
+               items[2:] = items[2].split(",")
+               hours   = int(items[0])
+               minutes = int(items[1])
+               secs    = int(items[2])
+               ms      = int(items[3])
+               return cls(hours, minutes, secs, ms)
+
+################
+# MAIN PROGRAM #
+################
+infile = open(sys.argv[1])
+outfile = open(sys.argv[2], "w")
+offset = float(sys.argv[3])
+
+subtitle_counter = 1
+
+try:
+       while True:
+               # copy subtitle number to output, check if they are consecutive
+               line = infile.next()
+               subtitle_number_from_file = int(line)
+               if subtitle_counter != subtitle_number_from_file: raise SubtitleFormatError
+               subtitle_counter += 1
+               outfile.write(line)
+
+               # parse start and end times, shift them, write to output
+               line = infile.next()
+               s1, arrow, s2 = line.split()
+               if arrow != "-->": raise SubtitleFormatError
+               t1 = Timestamp.fromString(s1).addSeconds(offset)
+               t2 = Timestamp.fromString(s2).addSeconds(offset)
+               outfile.write("%s --> %s\n"%(str(t1), str(t2)))
+
+               # copy lines to output until next subtitle (after blank line)
+               line = infile.next()
+               while line.strip() != "":
+                       outfile.write(line)
+                       line = infile.next()
+               outfile.write("\n")
+
+except StopIteration:
+       pass
+
+infile.close()
+outfile.close()
+
+