I find it hard to be too upset, better late than never. Would it have been better to upstream shortly after they wrote the code? Yes. Would it have been better if they also made a sizable contribution to fmmpeg? Yes. But at the end of the day they did contribute back valuable code and that is worth celebrating even if it was done purely because of the benefit to them. Let's hope that this is a small step and they do even more in the future.
As I said, the contribution is good, it's the communication via this blog post that I don't entirely like. It could have been different. It could have acknowledged better ways of engaging with ffmpeg (that would've benefitted both Meta and ffmpeg/the community, not _just_ ffmpeg).
But corporate blog posts often go this way. I'm not mad at them or anything. Just a mild dislike ;)