Good explanation for feature matching algorithms

These two videos are explaining how to detect keypoints and generate descriptors of an image very well:
- find keypoints: https://www.youtube.com/watch?v=nGya59Je4Bs
- compute descriptors: https://www.youtube.com/watch?v=CMolhcwtGAU

All the algorithms described in these videos are standards and would be worth reimplementing if we wanted to enhance our feature matching tools.