SD -> HD または HD -> SD の切り替えがあるときに、HD または SD の先頭オフセットを見つける

sd-hd.rb

#!/usr/bin/env ruby
# coding: utf-8
require 'open3'
require 'tempfile'

class Avconv
  def initialize(path, bin = 'avconv')
    @path = path
    @bin = bin
    @tempfile = Tempfile.new ['sd-hd', '.ts']
  end

  def skip(t)
    do_skip t
    out, err, statuses = Open3.capture3 @bin, '-i', @tempfile.path
    err.lines
  end

  def cuttable?(t)
    do_skip t
    system @bin, '-loglevel', 'quiet', '-i', @tempfile.path, '-acodec', 'copy', '-vcodec', 'copy', '-f', 'mpegts', '-t', '20', '-y', File::NULL
  end

  def do_skip(t)
    Open3.pipeline ['tail', '-c', "+#{188*t}", @path], ["head", '-c', '18800000', { out: @tempfile.path }]
  end
end

def bsearch(lo, hi, left_p, right_p)
  while lo < hi
    mid = (lo + hi)/2
    p [lo, hi, mid]
    if left_p.call mid
      hi = mid
    elsif right_p.call mid
      lo = mid+1
    else
      $stderr.puts "Error at mid=#{mid}"
      lo = mid+1
      #raise "Error at mid=#{mid}"
    end
  end
  lo
end

SD_SIZE = '720x480'
HD_SIZE = '1440x1080'
MAIN_STREAM = 'mpeg2video'

hd_p = lambda do |lines|
  lines.any? do |line|
    line.include? MAIN_STREAM and line.include? HD_SIZE
  end
end

sd_p = lambda do |lines|
  lines.any? do |line|
    line.include? MAIN_STREAM and line.include? SD_SIZE
  end
end

path = ARGV[0] or exit 1
avconv = Avconv.new path

MAX_PACKETS = 200000
first_lines = avconv.skip 0
last_lines = avconv.skip MAX_PACKETS

left_p = nil, right_p = nil
if sd_p.call first_lines and hd_p.call last_lines
  $stderr.puts "SD -> HD detected"
  left_p = hd_p
  right_p = sd_p
elsif hd_p.call first_lines and sd_p.call last_lines
  $stderr.puts "HD -> SD detected"
  left_p = sd_p
  right_p = hd_p
end

if left_p.nil? or right_p.nil?
  $stderr.puts "No switching is detected"
  exit 0
end

ans = bsearch(
  0,
  MAX_PACKETS,
  lambda { |t| lines = avconv.skip t; left_p.call lines and not right_p.call lines and avconv.cuttable? t },
  lambda { |t| right_p.call avconv.skip(t) }
)

puts "tail -c +$[188*#{ans}] #{path}"