> have you ever compile FFMPEG?

Yes

> why not go ahead and compile FFMPEG with PThread support and add it to UNA?

We provide basic version which works on most servers and can't overload the server by taking all CPU power. Only recently we used 64bit version of ffmpeg, before 32bit version was always used. 

I'm very greatful who make static builds available for free it save us a lot of time, so we are using this opportunity and can do other important things. 

To increase ffmpeg performance for the best results you need to compile own ffmpeg which is using your hardware capabilities for the best performance.