[lorenzhs]

I don't think so, the WebM/WebP patent grant seems to only revoke the licence to use these patents when you claim that Google or someone else is infringing upon your patents by using WebM/WebP: https://www.webmproject.org/license/additional/ (IANAL)

> "If you [...] order or agree to the institution of patent litigation [...] against any entity [...] alleging that any of these implementations of WebM or any code incorporated within any of these implementations of WebM constitutes direct or contributory patent infringement, [...] then any patent rights granted to you under this License for these implementations of WebM shall terminate as of the date such litigation is filed."