Create SRT with timecodes to overlay speedrun for timing

timer_srt.py

from datetime import datetime
import os

# input your times
# HH:MM:SS.FFF
video_length = "00:06:42.984" 
start_time = "00:00:20.649"
end_time = "00:06:05.899"
fps = 60
outfile = 'time.srt'

# remove old srt
if os.path.isfile(outfile):
	os.remove(outfile)

# convert hhmmss.fff to secs
def hhmmssff_to_secs(t): # https://stackoverflow.com/a/50069650
	timezero = datetime.strptime('00:00:00.000', '%H:%M:%S.%f')
	return (datetime.strptime(t, '%H:%M:%S.%f') - timezero).total_seconds()

# write to srt
def write_to_srt(f, iter, start, end, msg):
	with open(f, "a") as srt:
		srt.write( str(iter) +'\n' )
		srt.write( str(start) + ' --> ' + str(end) +'\n')
		srt.write( str(msg) + '\n\n')

time = 0.0
runtime = 0.0
i = 1

# before run starts print 00:00:00
while time <= hhmmssff_to_secs(start_time):
	start_string = datetime.utcfromtimestamp(time).strftime('%H:%M:%S,%f')[:-3]
	msg = datetime.utcfromtimestamp(runtime).strftime('%H:%M:%S,%f')[:-3]
	time += (1/fps)
	# dont increment runtime here
	end_string = datetime.utcfromtimestamp(time).strftime('%H:%M:%S,%f')[:-3]

	write_to_srt(outfile, i, start_string, end_string, msg)

	i+=1

# during run
while time <= hhmmssff_to_secs(end_time):
	start_string = datetime.utcfromtimestamp(time).strftime('%H:%M:%S,%f')[:-3]
	msg = datetime.utcfromtimestamp(runtime).strftime('%H:%M:%S,%f')[:-3]
	time += (1/fps)
	runtime += (1/fps)
	end_string = datetime.utcfromtimestamp(time).strftime('%H:%M:%S,%f')[:-3]

	write_to_srt(outfile, i, start_string, end_string, msg)

	i += 1

# after run print final time
while time <= hhmmssff_to_secs(video_length):
	start_string = datetime.utcfromtimestamp(time).strftime('%H:%M:%S,%f')[:-3]
	msg = datetime.utcfromtimestamp(runtime).strftime('%H:%M:%S,%f')[:-3]
	time += (1/fps)
	# dont increment runtime here
	end_string = datetime.utcfromtimestamp(time).strftime('%H:%M:%S,%f')[:-3]

	write_to_srt(outfile, i, start_string, end_string, msg)

	i+=1

# then to overlay it in ffmpeg:
# ffmpeg -i video.mp4 -vf subtitles=time.srt out.mp4