Convert video to preview gif like those xxx websites, using libav-tools and imagick

convert1.rb

filename = 'a.mp4'
target_path = '../processing'
(1..8).each do |i|
  t = i * 60
  target_file = File.join(target_path, "#{i}.jpg")
  `avconv -i #{filename} -ss #{t} -vcodec mjpeg -vframes 1 -an -f rawvideo -s 320x240 '#{target_file}'`
end
image_files = File.join target_path, '*.jpg'
`convert -delay 50 -loop 0 #{image_files} #{filename}.gif`

convert2.rb

preview_path = File.expand_path 'preview'

temp_path = '/tmp/processing'
`mkdir -p #{temp_path}`

(Dir.glob('*') - ['preview']).each do |dir|
  `mkdir -p #{File.join preview_path, dir}`
  puts "list #{dir}: #{Dir.glob(File.join(dir, '*'))}"
  Dir.glob(File.join(dir, '*')).each do |filename|
    # filename = '1.mp4'
    puts "converting: #{filename}"

    # convert video to images
    `avconv -i #{filename} -r 1 -s 320x240 #{File.join temp_path, '%08d.jpg'} `

    # sample images
    image_files = Dir.glob(File.join(temp_path, '*.jpg'))
    step = image_files.count / 8
    image_files = (0 .. 8).map { |i| image_files[i*step] }.join(" ")

    # convert image to gif
    `convert -delay 50 -loop 0 #{image_files} #{File.join preview_path, dir, File.basename(filename)}.gif`
    `rm #{File.join temp_path, '*.jpg'}`
  end
end;

covert3.rb

preview_path = File.expand_path 'preview'
temp_path = '/tmp/processing'

# cleanup
`rm -rf #{temp_path}`
`mkdir -p #{temp_path}`
`rm -rf #{preview_path}`
`mkdir -p #{preview_path}`

(Dir.glob('*') - ['preview']).each do |dir|
  # dir = (Dir.glob('*') - ['preview']).first
  `mkdir -p #{File.join preview_path, dir}`
  puts "list #{dir}: #{Dir.glob(File.join(dir, '*'))}"

  Dir.glob(File.join(dir, '*')).each do |filename|
    # filename = Dir.glob(File.join(dir, '*')).first
    puts "converting: #{filename}"

    # get duration
    duration = `avprobe #{filename} -show_format -loglevel panic`.split("\n").compact.select{|l| l =~ /duration/}.first.split('=')[1].to_i

    # for each sample time, save a image
    step = duration / 8
    (0..8).each do |i|
      `avconv -ss #{i*step} -i #{filename} -r 1 -vframes 1 -s 320x240 #{File.join temp_path, "#{i.to_s.rjust(8, '0')}.jpg"} -loglevel panic`
    end
    image_files = Dir.glob(File.join(temp_path, '*.jpg')).sort.join(' ')

    # convert image to gif
    `convert -delay 50 -loop 0 #{image_files} #{File.join preview_path, dir, File.basename(filename)}.gif`
    `rm #{File.join temp_path, '*.jpg'}`
  end
end;