How does
"Distributing buildable source under Apache 2.0 would surely qualify too"
reconcile with
"doesn't own the copyright to FFMPEG and simply doesn't have the legal authority to release it under any license other than the LGPL"
if they licenced their own code under apache 2.0 as buildable with the lgpl ffmeg code, without relicensing ffmeg as apache itself
You can distribute your own code under Apache along with FFMpeg under LGPL in one download