Deletes X frames from mplayer jpeg output

discard_frames.rb

#!/usr/bin/env ruby

def discard_x_frames(number)
  files = Dir.glob('*.jpg')
  files.in_groups_of(number + 1).each do |files|
    files[1..-1].each do |file|
      File.unlink(file)
    end
  end
end

class Array
  def in_groups_of(number, fill_with = nil)
    if fill_with == false
      collection = self
    else
      # size % number gives how many extra we have;
      # subtracting from number gives how many to add;
      # modulo number ensures we don't add group of just fill.
      padding = (number - size % number) % number
      collection = dup.concat([fill_with] * padding)
    end

    if block_given?
      collection.each_slice(number) { |slice| yield(slice) }
    else
      groups = []
      collection.each_slice(number) { |group| groups << group }
      groups
    end
  end
end

discard_x_frames ARGV[0]