He is turning the fk-ik pose on and off. The apply before action is something that should be off and stay off, he's showing how to fix it.
When the fk-ik pose is turned off (this is the red pose hilighted in your pose slider window), some of the constraints are at 100% and some are 0%, the 100% constraints are the ones to compensate. Now turn the fk-ik pose on and compensate the poses that are now at 100%. Close action window and your done, test model in action (do not test in the edit pose action window, any bone movement from translating or rotating will then become part of the pose). Also, delete all actions before editing pose.