My second technology deep-dive article on the new AV1 codec is up, this time at Mozilla Hacks. It's a continuation of the video codec technology pages that I started with Daala.
"The Constrained Directional Enhancement Filter is the one we're interested in here; like the loop restoration filter, it removes ringing and basis noise around sharp edges, but unlike the loop restoration filter, it's directional. It can follow edges, as opposed to blindly filtering in all directions like most filters. This makes CDEF especially interesting; it's the first practical and useful directional filter applied in video coding."