It is LGPL, but upgrades to GPL if you enable certain modules (x264 support being the canonical example). The way we handle this in ParaView is to build it shared and no GPL modules; anyone can then provide their own ffmpeg libraries to the ParaView binaries that they wish (same with Qt). That is sufficient there. If someone wants the GPL module, they’ll have to provide the sources for their resulting distributable to comply (we can’t for the official ParaView binaries as some of the third party projects in the build do not have public sources).