spits out a tab-separated file of video duration / # of videos with that duration, expects to be run in a folder containing the output of youtube-dl's --write-info-json flag

durations.rb

#!/usr/bin/env ruby
require "rubygems"
require "json"

duration_map = {}

Dir.glob("*.json") do |fn|
  File.open(fn) do |f|
    obj = JSON.parse(f.read())
    duration = obj["duration"]
    if duration_map[duration]
      duration_map[duration] += 1
    else
      duration_map[duration] = 1
    end
  end
end

sorted_durations = duration_map.keys.sort { |x,y| x.to_i <=> y.to_i }
sorted_durations.each do |dur|
  count = duration_map[dur]
  puts "#{dur}\t#{count}"
end