ffmpeg is LGPL; it is used by hundreds of commercial applications around the world. For that matter, it has no commercial competitors for many of its use-cases.

Even On2, a competing encoder company, includes instructions with its encoder on how to set up mplayer (which uses ffmpeg) for decoding input videos.

The main 'problem' is that you'll still require an MPEG licence for encoding and decoding. Once you've bought one and abide by the usual LGPL rules (don't claim ownership, make source & changes available if distributing) then there shouldn't be any more commercial issues than, say, using Linux.