http://www.webmproject.org/license/software/ : If You or your agent or exclusive licensee institute or order or agree to the institution of patent litigation against any entity (including a cross-claim or counterclaim in a lawsuit) alleging that this implementation of VP8 or any code incorporated within this implementation of VP8 constitutes direct or contributory patent infringement, or inducement of patent infringement, then any rights granted to You under this License for this implementation of VP8 shall terminate as of the date such litigation is filed.
donc en gros si tu les fait chier avec un brevet, tu perds le droit d'utiliser le vp8.
les malins
mais je me demande si la licence peut encore être considérée comme libre