I'm aware, sometimes they also provide funding for FOSS projects. Funding seems to be the option FFmpeg would prefer based on the title (though I've not explicitly seen a quote that says this).

If it's a specialty codebase written entirely in assembly, as this seems to be, sometimes it just makes sense to pay someone else to do it rather than spending 3x as long getting someone in house to do because the expertise isn't there. Or just put a bounty on it, another common way to provide funding in FOSS.