asciinema.org/app/uploaders/compressed_file_uploader.rb

class CompressedFileUploader < BaseUploader

  def decompressed_path
    return unless file

    cache_stored_file! unless cached?

    out_path = "#{current_path}.decompressed"

    unless File.exist?(out_path)
      decompress(out_path)
    end

    out_path
  end

  private

  def decompress(out_path)
    header = File.read(current_path, 2).bytes

    case header
    when [31, 139]
      system("gzip -d -c #{current_path} >#{out_path}")
    when [66, 90]
      system("bzip2 -d -c #{current_path} >#{out_path}")
    else
      raise "unknown compressed file format"
    end
  end

end