We should obtain the srt stream.

For example, we can use `mkvtoolnx`:

```
.\mkvextract.exe "..\..\OP2.mkv" tracks 4:subs.srt
```

```
00000000 ef bb bf 31 0d 0a 30 31 3a 33 33 3a 33 37 2c 30 |1..01:33:37,0|
00000010 30 30 20 2d 2d 3e 20 30 31 3a 33 33 3a 33 37 2c |00 --> 01:33:37,|
00000020 30 31 30 0d 0a 4c 61 62 65 6c 20 69 6e 66 6f 0d |010..Label info.|
00000030 0a 0d 0a 0d 0a 16 0f 0d 0a 04 15 07 1c 0d 0a 10 |................|
00000040 18 06 13 0d 0a 0d 0a |.......|
```

Original file was:
```
00000000 31 0a 30 31 3a 33 33 3a 33 37 2c 30 30 20 2d 2d |1.01:33:37,00 --|
00000010 3e 20 30 31 3a 33 33 3a 33 37 2c 30 31 0a 4c 61 |> 01:33:37,01.La|
00000020 62 65 6c 20 69 6e 66 6f 0a 0a 16 0f 0a 04 15 07 |bel info........|
00000030 1c 0d 10 18 06 13 00 1a 10 16 13 00 09 06 19 1e |................|
```

The flag was hide in the end of original subtitles.

Right decrypted data by SUB 0xA1

https://gchq.github.io/CyberChef/#recipe=From_Hex('Auto')SUB(%7B'option':'Decimal','string':'161'%7D)&input=MzEgMEEgMzAgMzEgM0EgMzMgMzMgM0EgMzMgMzcgMkMgMzAgMzAgMjAgMkQgMkQKM0UgMjAgMzAgMzEgM0EgMzMgMzMgM0EgMzMgMzcgMkMgMzAgMzEgMEEgNEMgNjEKNjIgNjUgNkMgMjAgNjkgNkUgNjYgNkYgMEEgMEEgMTYgMEYgMEEgMDQgMTUgMDcKMUMgMEQgMTAgMTggMDYgMTMgMDAgMUEgMTAgMTYgMTMgMDAgMDkgMDYgMTkgMUUK

Broken:

https://gchq.github.io/CyberChef/#recipe=From_Hex('Auto')SUB(%7B'option':'Decimal','string':'161'%7D)&input=RUYgQkIgQkYgMzEgMEQgMEEgMzAgMzEgM0EgMzMgMzMgM0EgMzMgMzcgMkMgMzAKMzAgMzAgMjAgMkQgMkQgM0UgMjAgMzAgMzEgM0EgMzMgMzMgM0EgMzMgMzcgMkMKMzAgMzEgMzAgMEQgMEEgNEMgNjEgNjIgNjUgNkMgMjAgNjkgNkUgNjYgNkYgMEQKMEEgMEQgMEEgMEQgMEEgMTYgMEYgMEQgMEEgMDQgMTUgMDcgMUMgMEQgMEEgMTAKMTggMDYgMTMgMEQgMEEgMEQgMEEK

This way task cannot be solved.