I couldn't get the PS Vue add-on to work (which is in the official kodi repository) until I recompiled ffmpeg with USE="openssl". I think a lot of other streams are encrypted in kodi which will also require ffmpeg openssl support.
Ideally, if kodi is built with libressl, it should also require ffmpeg to be built with libressl too. However, ffmpeg doesn't support that at the moment, see bug 569818. But for now, I'll add this dependency. https://github.com/gentoo/gentoo/pull/5143 Thanks for reporting the issue!