aegisub software package provides advanced subtitle editor, you can install in your Debian 9 (Stretch) by running the commands given below on the terminal,
$ sudo apt-get update $ sudo apt-get install aegisub
aegisub is installed in your system.
Make ensure the aegisub package were installed using the commands given below,
$ sudo dpkg-query -l | grep aegisub *
You will get with aegisub package name, version, architecture and description in a table
| Distro | Debian 9 stretch |
| Section | Video |
| Package | aegisub |
| Version | 3.2.2+dfsg-3+b2 |
| Description | advanced subtitle editor |
| Sub Section | Video |