$ cat ~/example.srt
1
00:00:01,600 --> 00:00:04,200
English (US)

2
00:00:05,900 --> 00:00:07,999
This is a subtitle in American English

3
00:00:10,000 --> 00:00:14,000
Adding subtitles is very easy to do
$ srtoffset ~/example.srt '00:00:05,500'
1
00:00:07,100 --> 00:00:09,700
English (US)

2
00:00:11,400 --> 00:00:13,499
This is a subtitle in American English

3
00:00:15,500 --> 00:00:19,500
Adding subtitles is very easy to do
$ srtoffset ~/example.srt '00:00:01,000' --rewind
1
00:00:00,600 --> 00:00:03,200
English (US)

2
00:00:04,900 --> 00:00:06,999
This is a subtitle in American English

3
00:00:09,000 --> 00:00:13,000
Adding subtitles is very easy to do

$ poetry init
$ poetry install

$ poetry run pytest