how to merge multiple subtitle files in python?

[D.LUFFY]

I have a batch of files "srt" I want to merge

sub1.srt

1
00:00:21,601 --> 00:00:24,130
- What happened? - It's a mess, I heard.

2
00:00:24,131 --> 00:00:25,900
- What's that? - Dead bodies?

3
00:00:25,901 --> 00:00:28,839
- What's going on? - I wish I knew.

sub2.srt

1
00:00:28,840 --> 00:00:31,310
No one knows. They won't say.

2
00:00:31,311 --> 00:00:35,276
- My gosh. - How can so many die?

3
00:00:45,191 --> 00:00:46,556
When you starve,

after merge

1
00:00:21,601 --> 00:00:24,130
- What happened? - It's a mess, I heard.

2
00:00:24,131 --> 00:00:25,900
- What's that? - Dead bodies?

3
00:00:25,901 --> 00:00:28,839
- What's going on? - I wish I knew.

4
00:00:28,840 --> 00:00:31,310
No one knows. They won't say.

5
00:00:31,311 --> 00:00:35,276
- My gosh. - How can so many die?

6
00:00:45,191 --> 00:00:46,556
When you starve,

I found this script that it works The problem is in the numbers The subtitle are not in order

filenames = ['sub1.srt', 'sub2.srt']
with open('output_file.srt', 'w') as outfile:
    for fname in filenames:
        with open(fname) as infile:
            for line in infile:
                outfile.write(line)

numbers appear unordered

1
2
3
1
2
3

Note, I know a program "Subtitle Edit" Specialized in merging a group of Subtitles. I want a script to add to My project I'm working on. I hope for help, thank you

[_Al_]

try to rename those numbers at the same time as making copy

filenames = ['sub1.srt', 'sub2.srt']
numbers = 0
with open('output_file.srt', 'w') as outfile:
    for fname in filenames:
        with open(fname) as infile:
            for line in infile:
                try:
                    if 1 <len(line)<6 and isinstance(int(line),int):
                         numbers += 1
                         line = f'{numbers}\n'
                except ValueError:
                    pass
                finally:
                    outfile.write(line)
            outfile.write('\n\n')

this can still fail if there is a lone number less than 5 digits in a title, you might check for correct position , above time,etc., but it seams there must be easier way to do it

[D.LUFFY]

Thanks it works