I USE BLENDER 2.90.0
THIS HAPPENS ACROSS ALL WORKSPACES
Ok, so I'm rendering a simple video with some hue changes (In the VFX tab using masks), and when I was done I tried to render it out, and it goes black in the video. To try and remedy this, since rendering images was working, I rendered as an image sequence and that worked. So I went into the Video Editing workspace (on a new blender file) and imported my image sequence with my audio and the same problem occurred with my FFMPEG output. It looked absolutely fine on the tab where it was rendering, so I have no idea what causes it. I checked compositing because that was my last mistake but nothing there because I never tampered with it.
Images (I blacked some stuff out for privacy reasons)
I've tried to fix this but I can't, and a possible fix would be to re-install if all else fails. Hope you people can do your blender magic because I don't have any...