This video is dated and the design has many flaws (gas isn't clean enough to really run an engine for a long time etc).

The Wood Gasifeir's handbook is a great guide on building a better DIY one.

But, if you're serious about this, you do it at a larger scale with professional equipment: https://www.holz-kraft.com/en/products/hka-600.html

This is perfect for agroforestry farms and larger properties with a lot of fast growing trees that also need heating for something (greenhouse, spa, housing, ...) and they can do bitcoin mining with the elec. #woodgas