How to append or concatenate two srt files that already synchronized?

[mymirai-nikki]

I have two srt files that already synchronized, I just need to adjust the offset of second srt file.

I tried:

ffs ./S01E01.mkv -i 1.srt 2.srt --overwrite-input
cat 2.srt >> 1.srt
mv 1.srt ./S01E01.srt

but the results isn't properly synchronized.

[mymirai-nikki]

The solution so far:

ffs --apply-offset-seconds 2600 -i /tmp/2.srt -o /tmp/out.srt
cat /tmp/out.srt >> concatenated.srt