Camera tracking, or matchmoving, means extracting camera movement from a video so 3D elements can be added to a shot. Done manually in Blender this is time consuming. Easy Camera Tracker handles it automatically in a few clicks, and tracking runs in the background so you can keep working while it solves.
Once a shot is tracked, the addon creates an animated camera that moves with the video, builds an image sequence set as the camera background, generates a point cloud, and matches render settings to the footage (resolution, fps and color profile). Camera orientation can be set easily, and a floor can be generated with the video projected onto it. Object tracking is available through an implementation of the Polychase addon.
Under the hood it uses Colmap, an open-source structure-from-motion package in development since 2016. It can also export an undistorted image sequence for compositing, with the option to reapply the original distortion later, track zoom shots, and exposes full manual tracking settings.