It also appears to be the only game in town. Many commercial offerings are really just veneers over custom ffmpeg implementations.
Tuning it is also pretty crazy. Some folks can make entire careers out of just tuning ffmpeg.
I think the biggest issue with video software (besides it being difficult and performance-intensive), is the prevalence of a lot of old, highly-enforceable patents.
Video has been around a while, and companies like Ampex patented a heck of a lot of stuff that can easily be applied to current video.
ffmpeg actually has a couple of build configs that are designed to remove coercive-licensed components.
I'm not so happy about that, but it's the world we live in.
I do have a project that I was playing around with (and will get back to, sooner or later), where I made a simple MacOS wrapper for ffmpeg:
https://github.com/RiftValleySoftware/RVS_MediaServer
I wrote about that, here: