Render FFMPEG from rendered image files

Hello, I remember seeing in a tutorial that you could render an animation as images and then render it again as an ffmpeg by reusing the images that were rendered before.
I can’t remember the video, so I’m wondering how to do this. Ideally I’d like to avoid invoking ffmpeg outside of blender because that seems like it would be a pita to get my audio in the video as well.

Ideally, I’d like to avoid creating another video sequence with the audio and placing all the images in there as that would be tedious