Extract fragments from a video using FFmpeg

extract-fragments-ffmpeg.rb

#!/usr/bin/ruby

require "tmpdir"

def usage()
  STDERR.puts <<EOU
Usage: #$0 input-file output-file ranges+

Ranges can be defined with:

  start:end         Define a range in absolute times
  start+duration    +duration seconds from start
  start:            From start to the end
  :duration         Only the first 'duration' seconds
EOU
  exit 1
end

args = ARGV.dup

if args.size < 3
  usage()
end

input_file = args.shift
input_file_ext = File.extname(input_file)

output_file = args.shift

if File.exist?(output_file)
  STDERR.puts "#{output_file} exists"
  exit 2
end

ranges = args.map do |range|
  case range
  when /^(\d+):(\d+)$/
    start = $1.to_i
    end_ = $2.to_i
    if end_ < start
      STDERR.puts "Invalid value in #{range}"
      usage()
    end

    { start: start, duration: end_ - start }

  when /^:(\d+)$/
    duration = $1.to_i
    { duration: duration }

  when /^(\d+):$/
    start = $1.to_i
    { start: start }

  when /^(\d+)\+(\d+)$/
    start = $1.to_i
    duration = $2.to_i
    { start: start, duration: duration }

  else
    STDERR.puts "\033[31mInvalid range format '#{range}'\033[m"
    usage()
  end
end

dir = Dir.mktmpdir("video-extract--")
puts "Temp files in #{dir}"

running = []
partial_videos = []

ranges.each_with_index do |range, index|
  output_name = "#{dir}/video#{index}#{input_file_ext}"
  stdout_name = "#{dir}/video#{index}.log"

  partial_videos << output_name

  running << fork do
    s, d = range.values_at(:start, :duration)
    ffmpeg_args = ["ffmpeg", "-y"]

    # Start
    ffmpeg_args << "-ss" << s.to_s if s

    # Input file
    ffmpeg_args << "-i" << input_file

    # End
    ffmpeg_args << "-t" << d.to_s if d

    # Default "copy" codec
    ffmpeg_args << "-c" << "copy"

    # Output
    ffmpeg_args << output_name

    puts "Running #{ffmpeg_args.join(" ")} > #{stdout_name}"
    STDIN.reopen("/dev/null", "r")
    STDOUT.reopen(stdout_name, "a")
    STDERR.reopen(stdout_name, "a")
    exec(*ffmpeg_args)
  end

end

running.each do |pid|
  Process.waitpid(pid)
end

concat_file = "#{dir}/concat"
File.open(concat_file, "w") do |concat|
  partial_videos.each do |filename|
    concat.puts "file '#{filename}'"
  end
end

cmd = "ffmpeg", "-f", "concat", "-i", concat_file, "-c", "copy", output_file
puts "Running #{cmd.join(" ")}"
system(*cmd)

puts "Removing intermediate videos..."
partial_videos.each do |filename|
  File.unlink(filename)
end