Instead of using an external browser such as MSEdge, Firefox, Chrome or (in past times) Internet Explorer, StreamFab uses a built-in browser named (Q)CEF. CEF stands for Chrome Embedded Framework. QCEF is just CEF written to work in a Quicktime environment. QEF.log is the log that follows the actions of this browser. There is little there that would be of any interest to the developer unless there was a problem with the website display. It has nothing to do with cracking the DRM of the video file and it's download.