cleans up timecodes on subtitle text files to trim one frame from the in-point of each line. Adobe Encore was giving me PGC errors on my timeline. Putting a frame of space between each subtitle was the only fix that worked for me.

trim_frame_subtitle.rb

new_file_path = "path/to/subtitle_fixed_file.txt"
File.truncate(new_file_path, 0)
new_file = File.open(new_file_path, "w")
file = File.open("path/to/subtitle_file.txt", "r").readlines.each do |line|

  reg = /;(\d{2}) \d{2};/
  match = line.match(reg)
  
  if match.class == MatchData
    m = match[1]
    frame_number = m.to_i
    if frame_number < 23
      frame_number += 1 
    end
    
    new_frame = frame_number.to_s.rjust(2, "0")
    new_line = line.gsub(/(;)(#{m})(\s\d{2})/, "\\1#{new_frame}\\3")

  else
    new_line = line
  end
  
  new_file.puts new_line
  
end

new_file.close