Refer to - http://www.infinitegrid.org/drupal/content/BVJ

BVJ is extensions to the BVH animation format used by SL technology. 
It's in the ClientHamr section coz on the server side, they are just
dealt with as blobs to be sent to the viewers.  This may change if we
implement animating link sets, and interaction with the sim physics.

Also -
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Some useful links for actually writing animation code -

https://en.wikipedia.org/wiki/Portal:Computer_graphics
https://en.wikipedia.org/wiki/3D_computer_graphics
https://en.wikipedia.org/wiki/Skeletal_animation
https://en.wikipedia.org/wiki/Morph_target_animation
https://en.wikipedia.org/wiki/Inverse_kinematics

http://bvhacker.com/
http://www.character-studio.net/bvh_file_specification.htm