如何启用FFMPEG日志记录，在哪里可以找到FFMPEG日志文件?

I want to be able to log FFMPEG processes because I am trying to work out how long a minute of video takes to convert to help with capacity planning of my video encoding server. How do I enable logging and where is the log file saved. I have FFMPEG installed on a CentOS LAMP machine.I want to be able to log FFMPEG processes becau