Aegisub

A free, cross-platform open source tool for creating and modifying subtitles

Not tested on a device yet. What that means

Aegisub in Breadstick

Breadstick runs Debian's own aegisub package for ARM64, the build a Debian 13 computer with an ARM processor installs, so Aegisub should look and behave as it does on a Linux PC. On Samsung DeX, Floating mode opens it as its own window beside your Android apps, and Desktop mode runs it on a full Linux desktop.

Sound plays through the device's own audio output, and video is decoded in software, so large or high frame rate files can struggle on slower devices. More about audio and video apps in Breadstick.

About Aegisub

From the project's description

Aegisub is a free, cross-platform open source tool for creating and modifying subtitles. Aegisub makes it quick and easy to time subtitles to audio, and features many powerful tools for styling them, including a built-in real-time video preview.
Aegisub was originally created as a tool to make typesetting, particularly in anime fansubs, a less painful experience. At the time of the start of the project, many other programs that supported the Advanced Substation Alpha format lacked (and in many cases, still lack; development on several competing programs have since been dropped for various reasons completely unrelated to Aegisub) many vital functions, or were too buggy and/or unreliable to be really useful.
Since then, Aegisub has grown into a fully fledged, highly customizable subtitle editor. It features a lot of convenient tools to help you with timing, typesetting, editing and translating subtitles, as well as a powerful scripting environment called Automation (originally mostly intended for creating karaoke effects, Automation can now be used much else, including creating macros and various other convenient tools).
Some highlights of Aegisub:
Simple and intuitive yet powerful interface for editing subtitles
Support for many formats and character sets
Powerful video mode
Visual typesetting tools
Intuitive and customizable audio timing mode
Fully scriptable through the Automation module

From the project's AppStream metadata in Debian's aegisub package, under CC0-1.0.

Developer: Aegisub Group
Keywords: subtitles, text
Menu categories: Audio and video editing, Audio and video

Related apps

All Linux audio and video apps

Sources and licenses

Name, summary and description: the project's AppStream metadata in Debian's aegisub package, under CC0-1.0.
Icon: the project's own, from Debian's AppStream icon cache for the aegisub package; the project's license is BSD-3-Clause AND MIT AND MPL-1.1.
Versions and sizes: Debian's archive for ARM64, as on packages.debian.org.
Popularity: Debian Popularity Contest counts.