Subtitle Edit is a free (open source) editor for video subtitles - a subtitle editor :)
With SE you can easily adjust a subtitle if it is out of sync with the video in several different ways.
You can also use SE for making new subtitles from scratch (do use the time-line/waveform/spectrogram) or translating subtitles.
For a list of features see below or check out the Subtitle Edit Help page.
On https://www.nikse.dk/ you can download latest beta version and read about/discuss new features.
Also, you can watch a few videos about installing and using Subtitle Edit.
A Subtitle Edit dll (LibSe.dll) is available for programmers (BSD New/Simplified license).
Compile it from source code or use the NuGet package.
Download latest version of Subtitle Edit
Note: SE requires Microsoft .NET Framework Version 4.8
Get the full C# source code - GPL or LGPL license
Blu-ray sup reading code is under the Apache License and Matroska subtitle parsing uses zlib code with a BSD style license.