If there is no blackboard, you can use A4 paper or sketch book to write on the blackboard in your hand and put it near the camera for students to watch. You can turn the page after writing a page, and then take it out and explain it again at the end of the course.

Blackboard doesn't mean blackboard. Traditionally, it is a plane that can be written repeatedly. The board is relatively hard and is mostly used for teaching. Mostly black, dark green and white. Before the invention of writing, people found that charcoal can be used for painting, and some ancient murals can be found in some ancient caves in Europe. The rock wall painted with these murals can already be called a blackboard in the traditional sense.