I think it depends on your topic. For highly technical courses, the content of the course itself is likely to become outdated before video standards do. I record at 1080p because I'm in that boat, and that's enough resolution to keep things good for the forseeable future. Streaming 4K video across the world reliably isn't going to happen anytime soon. But, if I had a 4K camera and 4K monitor, and was teaching something more evergreen like a lifestyle topic, I'd probably shoot at higher resolution and just export to 1080, with the ability to increase it later on. Shooting live video at 4K also allows you do do more editing tricks, like simulating multiple cameras by cropping and zooming the image. You'd have to have a beefy computer with lots of storage to do that, though.
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