Rubyでmp4コンテナを表面的にパースするだけのコード

mp4parse.rb

def atom(file, indent = 0)
  return nil if file.eof?
  headersize = 8
  size = file.read(4).unpack('N')[0]
  type = file.read(4)
  if size == 1
    size = file.read(8).unpack('Q>')[0]
    headersize += 8
  elsif size == 0
    return nil
  end
  
  datasize = size - headersize
  
  puts "#{" "*indent}#{size}:#{type}"
  
  data = case type
    when "ftyp"
      file.read(datasize)
    when "moov","trak","edts","minf","dinf","stbl","mvex","mdia"
      multiatom(file, datasize, indent + 2)
      nil
    else
      file.seek(datasize, :CUR)
      nil
  end
  
  if data
    disp = data.gsub(/[^[:graph:]]/, '.')
    puts "#{" "*(indent+2)}#{disp}"
  end

  return [size,type,data]
end

def multiatom(file, size, indent = 0)
  loop {
    return if size == 0
    return if file.eof?
    (asize, type, data) = atom(file, indent)
    return if asize == nil
    size -= asize
  }
end

def main
  file = open(ARGV[0],"rb")
  multiatom(file, file.size)
end

main