My ani2ico implementation written in Ruby

ani2ico.rb

#!/usr/bin/env ruby

MetaStruct = {
  file_magic:   :txt, # File magic, should be "RIFF"
  payload_size: :int, # Size of the file (excluding the file magic)

  riff_chunkType:   :txt, # Should be "ACON"
  riff_chunkID:     :txt, # Should be "anih"
  riff_chunkSize:   :int, # Should be 36

  anih_chunkSize:   :int, # same as riff_chunkSize
  anih_numFrames:   :int, # number of .ico images saved
  anih_numSteps:    :int,
  anih_width:       :int,
  anih_height:      :int,
  anih_bitCount:    :int,
  anih_numPlanes:   :int,
  anih_displayRate: :int,
  anih_flags:       :int,

  listChunkID:   :txt, # Should be "LIST"
  listChunkSize: :int, # Size of all .ico images plus RIFF subchunk headers
  listHeaderID:  :txt  # Should be fram
}

ParsedMeta = {}
Filename   = File.basename(ARGV[0], '.ani')
ANI_fileIO = File.open(ARGV[0], 'r')

warn "File infomation:\n\n"

MetaStruct.each_pair do |name, type|
  data = ANI_fileIO.read(4)
  data = data.unpack('L')[0] if type == :int

  ParsedMeta[name] = data
  warn "  #{name}: #{data}"
end

warn "\n"

ParsedMeta[:anih_numFrames].times do |i|
  File.open('%s_%02i.ico' % [Filename, i], 'w') do |fileIO|
    chunkID   = ANI_fileIO.read(4)
    chunkSize = ANI_fileIO.read(4).unpack('L')[0]

    abort 'Error!' unless chunkID == 'icon'
    warn "Extracting frame #{i+1}/#{ParsedMeta[:anih_numFrames]}..."

    fileIO.write ANI_fileIO.read(chunkSize)
  end
end