Utility script that can adjust (shift forwards/backwards) the timing of Matroska chapters (given in XML chapter files, obtainable with `mkvextract somefile.mkv chapters out.xml`)

adjustChapterTimings.rb

#!/usr/bin/env ruby

require "fileutils"
require "nokogiri"

class Timestamp
  def self.parse(raw)
    return nil unless raw.match?(/\A\d\d:\d\d:\d\d.\d+\z/)
    hours, minutes, seconds = raw.split ":"
    ts = 0r
    ts += Integer(hours, 10) * 3600
    ts += Integer(minutes, 10) * 60
    ts += Rational(seconds)
  end

  def self.format(timestamp)
    hours = (timestamp / 3600).floor
    minutes = ((timestamp % 3600) / 60).floor
    seconds = timestamp % 60
    sprintf "%02d:%02d:%012.9f", hours, minutes, seconds
  end
end

def usage_and_exit
  $stderr.puts "Usage: adjustChapterTimings.rb <amount> [files...]"
  exit 1
end

amount = begin
  Rational(ARGV.shift)
rescue
  usage_and_exit
end

ARGV.select! {|f| File.file? f }
usage_and_exit if ARGV.empty?

ARGV.each do |f|
  FileUtils.cp f, "#{f}.orig" # backup
  doc = Nokogiri::XML::Document.parse File.read(f)
  doc.css("ChapterTimeStart, ChapterTimeEnd").each do |element|
    ts = Timestamp.parse element.content
    element.content = Timestamp.format(ts + amount)
  end
  File.write(f, doc.to_xml)
end