Idx/Sub Subtitle File Time Adjust (ISFiTA) v0.01

This is a quick and dirty (even the acronym) perl script I use to time-shift/stretch idx/sub subtitle files.

#!/usr/bin/perl


###########################################################################################
#
# Idx/Sub Subtitle File Time Adjust (ISFiTA) v0.01
#
# Author: Tsan-Kuang Lee
# Date: Jan 2, 2006
#
# What does it do?
#
#     A video file may have different subtitle files, which not only differ in format
#     but also differ in their timestamps.  Usually this is because the creators of
#     the subtitle files are syncing their subtitles to different video files (of the
#     same content, but some with, say, trailors, and others without).
#
#     For example, there are two video files: v1 and v2.  Let's say v1 has 2 minutes more
#     trailors from the beginning before the main content.  Subtitle creators make s1 for
#     v1 and s2 for v2.
#
#     However, we only have v1 and s2 at hand.  We want s2 to sync with v1.
#
#     If s2 is in plain text subtitle format, e.g. SRT, TXT, SSA, etc.  Many excellent 
#     utilities have been written, such as: SubCreator, http://www.radioactivepages.com/
#     ISFiTA deals with idx/sub format.
#
#
# How to use it?
#
#     ISFiTA simply reads the idx file (it's a plain text file) and recalculate the 
#     timestamps, according to the parameters we provide.  We'll need to provide the
#     several parameters.  Here's what you would usually input at the command prompt:
#
#     % perl ISFiTA-v0.01.pl 3 film0.idx 00:03:55:735 01:32:53:067 film.idx 00:03:34:535 01:32:32:067
#
#       Here's what they mean:
#       
#       "%" is the command prompt;
#       
#       "perl ISFiTA-v0.01.pl" launches this script;
#       
#       "3" is the index code of the language you want to deal with.  If you open the idx file
#       with a text editor, you would see something like "id: zh, index: 3".  zh is the language
#       code for Chinese (Zhong-wen), and "3" is what we want here.
#       
#       "film0.idx" is the original idx file we want to read from.
#       
#       "00:03:55:735" is the timestamp (the last three digits are in milliseconds) of one 
#       specific subtitle line in "filem0.idx".  Let's say it maps to the line "Let the show begin!".
#       Many tools let you see which line "00:03:55:735" maps to, e.g. VobSub. (Of course, you need 
#       to have film0.sub for VobSub to display the image.)
#       
#       "01:32:53:067" maps to another line in "film0.idx", say "See you next time!".
#       
#       "film.idx" is the target file we want to write to.
#       
#       "00:03:34:535" is the target timestamp for "Let the show begin!".  You can get this target
#       timestamp from watching the video file, or from a correctly synced subtitle file.
#       
#       "01:32:32:067" is the target timestamp for "See you next time!".
#
#    "Let the show begin!" doesn't have to be the first line in the whole subtitle; likewise, 
#    "See you next time!" doesn't have to be the last.  However, the more apart they are from 
#    each other, the more accuracy of caculation we get, since the minor time-offs will be
#    divided into ignorably small differences.
#
#    Don't forget to provide film.sub to complete the idx/sub pair.  Just use the original sub and
#    correctly rename it.
#
# About
#
#    This is a quick and dirty perl script (even its acronym sucks) I use to time-shift/stretch 
#    idx/sub subtitle files.  Do whatever you want with it, at your own risk.  If you do improve
#    it or rewrite it, I encourage you to share it with the public.  Authors of free utilities have
#    my highest respects.
#
# Todos for you
#
#    Here are some suggestions if you want to contribute something to the Open Source world, or the
#    freeware world:
#
#      SubCreator has much more sophisticated transformations. For example, you can decide the time
#      range in which you want to adjust the time code.
#
#      Obviously Perl is not user-friendly for most people. You may want to re-write it in another
#      language and compile it into an excuteable.
#
#      GUI makes it more approachable.
#
#      Bug the authors of VobSub, SubCreator, etc. to include idx/sub time adjust/stretch functions
#      into their utilities.
#
#
###########################################################################################


# Command line arguments
unless (@ARGV == 7) { die "Usage: $0 lang_index in_file in_start in_end out_file out_start out_end\n(timestamp format: hh:mm:ss:mis)\n" }
($lang_index, $in_file, $in_start_timestamp, $in_end_timestamp, $out_file, $out_start_timestamp, $out_end_timestamp) = @ARGV;

# Open files
unless (open INFILE, "<", $in_file) {
 die "Couldn't open input file $in_file: $!; aborting";
}
unless (open OUTFILE, ">", $out_file) {
 die "Couldn't open output file $out_file: $!; aborting";
}


# calculate necessaary transformation (shift, slope)
# simple linear transformation formula :
#
# new_bx = (ax - a1) * (b2-b1)/(a2-a1) + b1 , where
#  a1 = in_start ; a2 = in_end
#  b1 = out_start; b2 = out_en
#  ax = old_time_point

$shift_milliseconds = &convert_to_milliseconds($out_start_timestamp);
$slope = (&convert_to_milliseconds($out_end_timestamp) - $shift_milliseconds) / (&convert_to_milliseconds($in_end_timestamp) - &convert_to_milliseconds($in_start_timestamp));
$in_start_milliseconds = &convert_to_milliseconds($in_start_timestamp);


# start processing

$section = "header";
while ()
{
 if ($section eq "header" || $section eq "other_lang")
 {
  # check language id
  # id: zh, index: 2
  if ($_ =~ m/^id: *.+, index: *(.+)$/)
  {
   if ($1 eq $lang_index)
   {
    $section = "processing";
    print "Processing $_"; 
   }
   else
   {
    $section = "other_lang";
   }
  }
 }
 elsif ($section eq "processing")
 {
  # stop when another language id tag appears
  if ($_ =~ m/^id: *.+, index: *(.+)$/)
  {
   $section = "other_lang";
  }
  elsif ($_ =~ m/^(timestamp: )(\d\d:\d\d:\d\d:\d\d\d)(,.+)$/s)
  # only process lines with timestamps, e.g.
  # timestamp: 01:22:20:634, filepos: 00011a000
  {
   $_ = $1 . &calculate_new_timestamp($2) . $3;
  } 
 }
 print OUTFILE $_;
}

sub calculate_new_timestamp
{
 my ($old_timestamp) = @_;
 $new_milliseconds = (&convert_to_milliseconds($old_timestamp) - $in_start_milliseconds) * $slope + $shift_milliseconds;
 return &convert_to_timestamp($new_milliseconds);
}

sub convert_to_milliseconds
{
 my ($string) = @_;
 $string =~ m/(\d+):(\d+):(\d+):(\d+)/;
 $milliseconds = $4 + $3*1000 + $2*1000*60 + $1*1000*60*60;
 return $milliseconds;
}

sub convert_to_timestamp
{
 my ($milliseconds) = @_;
 
 # Although perl supports integer division, the scope of "use integer" 
 # is global and that would cause slope calculation become integer.
 # Therefore, we use redundant division as below.  floor() is possible but
 # we don't use it here for cross-distribution compatibility 
 # (some perl distributions don't have that package installed)

 my $res_h = $milliseconds % (60*60*1000);
 my $hour = ($milliseconds - $res_h) / (1000*60*60);
 my $res_m = $res_h % (1000*60);
 my $min = ($res_h - $res_m) / (1000*60);
 my $res_s = $res_m % 1000;
 my $sec = ($res_m - $res_s) / 1000;
 my $ms = $res_s;
 
 return sprintf("%02d:%02d:%02d:%03d", $hour, $min, $sec, $ms);
}