Q:

How to approach animations and OpenGL

There are tons of tools and instructions for making 3d models and animations in various software products. My question is: in video-game engines, when would you use a pre-rendered animation, and when would you use armature data in the model to manipulate your model in to the desired action?
Secondary questions:
Are there any games that even use the model's rigging, in-game, or is everything pre-rendered? 
Are there any human-readable file formats that contain armature data?
Lastly, from a OpenGL-level and up perspective, how would you implement a system for animating something like walking? 
I am building an OpenGL graphics engine from scratch as a personal project, so if answers can cater to that context, it would be fantastic. 

A:

Yeah, most games use a model's rigging and apply animation tracks to the bones in real time based on things happening in the game or player input.  Animations can also be blended between to make new animations or transition from one animation to another.  Animations can also be combined such that the lower half of a body is playing one animation and the upper half is playing a different animation.  There is also something called parametric animation where a lot more of the animations are derived from a smaller set of animated bone data.  There is also various levels of physics based animation such as ragdoll and inverse kinematics.  I've specialized as an animation programmer at previous employers, check out this more detailed info based on my experiences and observations: http://blog.demofox.org/2012/09/21/anatomy-of-a-skeletal-animation-system-part-1/

