Yes, but not an encoder, and that's the piece preventing it from being used to its potential. It's also nice when you no longer have to reverse-engineer the decoder. FFmpeg is one of my favorite things on earth, but minor differences between its implementations of closed-source codecs unfortunately prevent it from being a viable alternative in high-end post-production in many situations. ProRes encoding in FFmpeg for instance, although it certainly "works" as far as one can tell, still usually fails a few tests during the QC processes the bigger media companies use, and that generally means you can't use it, full-stop.