Is there a progressive encoding mode?

Hello.

I am using ffmpeg to create a video out of rendered frames from p5.js. It works but I am hitting memory limits on iOS. p5.js is dumping frames that are fed into ffmpeg to write to local storage and only when all the frames have been written can ffmpeg go in and convert to an MP4 file. My question-> Is there a way to convert progressively so that I can write a frame encode a frame then delete the frame before moving onto the next frame? That way the memory limit is avoided.