

The best way to learn is through learning by doing. This is one of the tried and tested means because you get to practice something while trying to learn it and ultimately get a grasp on a particular skill. Examples of these include learning how to ride a bike or learning to swim. One can not just watch something, learn it through the book and then expect to understand it and know it at the first instance of exposure to that particular skill.
This is where instructional videos come in. Any instructional video aims to teach the subscriber a particular skill, or a particular knowledge while watching the video. The techniques employed are first learning by example and then learning by doing.
True that one is not expected to learn something just by watching it on video. This includes simple tasks such as baking a cake or cooking a meal, as with every skill expected to be mastered practice and action is important.
Martial arts instructional videos provide the watcher the ins and about of the art form. Providing the most basic of knowledge such as the history of the particular martial art, and then teaching the science behind every move and then giving away techniques on how a martial art move is done.