The open-source video-editing-style subtitle editor. A better README will be made shortly, this is only public for right now to test the auto updater. Feel free to use it though and give me feedback!
YouTube is hilariously inconsistent with how their different apps render formatting, even with their proprietary SRV3 format. For more information on this based on my personal compatibility testing, see docs/COMPAT.md.
The app will also warn you of certain issues in the Problems tab, and you can also get a rough preview of different app renderings by using the dropdown at the top of the Preview window.