Compresses everything in a folder with ffmpeg using some arbitrary parameters. Outputs to a different folder. 85% savings in my experience, with no major loss in quality.

ffmpeg_compress.rb

# How to run:
#
# $ cd ~/folder/that/contains/videos/in/original
# $ cd ..
# $ ls original/
# video1.mp4 video2.mp4
# 
# $ ruby ffmpeg_compress.rb
# $ ls compressed/
# video1.mp4 video2.mp4
# 

ORIGINAL_FOLDER = 'original'
COMPRESSED_FOLDER = 'compressed'

files = Dir["#{ORIGINAL_FOLDER}/*"]

files.each do |path|
  newPath = path.sub(ORIGINAL_FOLDER, COMPRESSED_FOLDER)

  cmd = "export INPUT=\"#{path}\" OUTPUT=\"#{newPath}\" && ffmpeg -y -i $INPUT -r 30000/1001 -b:v 400k -bt 500k -vcodec libx264 -acodec libfaac -ac 2 -ar 44100 -ab 128k $OUTPUT"

  system(cmd)
end

very useful! :)