Makes evenly spaced markers for Adobe Premiere Pro, useful for cutting to music. Give it a BPM & duration and it'll give you some marker data for pasting into an XML document.

markerbeat.rb

#!/usr/bin/env ruby -wU

# markerbeat.rb by Ian Haigh 2015
# distributed under the MIT license, more info here
# http://opensource.org/licenses/MIT

require 'optparse'

class FrameMarker
	attr_accessor :bpm, :duration, :framesPerSecond

	def initialize
		@duration = 120 # default 2 mins
		@framesPerSecond = 25.0
		@bpm = 60.0
	end

	def frameAtTime(t)
		(t * @framesPerSecond).round()
	end

	def allFrames(upTo)
		counter = 0
		ary = []
		until counter > upTo.to_f
			counter += beatDuration
			ary.push((counter * @framesPerSecond).round())
		end
		return ary
	end

	def beatDuration
		60.0/@bpm
	end

	def to_s
		return <<-END
		FPS: #{@framesPerSecond}
		BPM: #{@bpm}
		Duration: #{@duration}
		Beat duration: #{beatDuration}
		END
	end

	def xml
		s=""
		allFrames(@duration).each do |frame|
			s += <<-THE_END
			<marker>
				<comment></comment>
				<name></name>
				<in>#{frame}</in>
				<out>-1</out>
			</marker>
			THE_END
		end
		s
	end
end

f = FrameMarker.new()

options = {}
optparse = OptionParser.new do |opts|
	opts.on("-h", "--help", 'Display this screen') do
		puts opts
		exit
	end
	opts.on('-b=BPM', "--bpm BPM", 'Beats per minute') do |bpm|
		f.bpm = bpm.to_f
	end
	opts.on('-x', "--xml", "Print XML suitable for Premiere Pro") do |variable|
		options[:xml] = true
	end
	opts.on('-d=DURATION', "--duration DURATION", "Duration of the music in seconds") do |d|
		# options[:duration] = d
		f.duration = d
	end
	opts.on('-f=FPS', "--frames FPS", "Frames per second (default: 25)") do |d|
		# options[:fps] = d
		f.framesPerSecond = d.to_f
	end
end

if ARGV.empty?
	puts optparse
	exit
end

optparse.parse!
puts f.xml if options[:xml]