I felt like if nobody was going to make a tool like this I was gonna be the one to make it, so here you go:

Basics

You can input any top and bottom text, or also only one of them, and everything will be generated according to how it'd look in game

Speed

Don't like the default speed (15 ms)? You can adjust that too

Customization

Further more, you can use a custom color or background (resize it to 1800x600p for best results)

Sadly transparency is impossible with the MediaRecorder API to the extent of my knowledge