The Midjourney video parameter explained

Use the --video parameter to create a short movie of your initial image grid being generated. React to the finished job with the envelope ✉️ emoji to have the Midjourney Bot send a link to the video to your Direct Messages.

Note: this only outputs a video from your generations.

--video only works on image grids, not upscales.
--video works with Model Versions 5, 5.1, 5.2, and niji 5.
--video works with Legacy Model Versions 123test, and testp.

Midjourney video

Can you create a video from Midjourney output?

No, you can not. Use tools like Pikalabs, RunwayML or Adobe After effects to creating video from your upscaled Midjourney outputs.