Ubuntu Basics Delay FFMPEG with SLEEP and SS
Delay onset of recording in 2 different ways. The command "sleep 5 &&" delays onset of running the actual terminal command. You will see a blank terminal for 5 seconds. The inclusion of "- ss 5" before the output file delays recording after the FFMPEG command begins. The manual pages of FFMPEG says you can put - ss in front of the input file also, but that it is not as accurate in counting.
The - ss switch is used differently when you are editing an existing file. The -ss switch (when used on an existing file) is used to chop off the first few seconds of a file you have already made. This video shows that - ss can also be used to delay onset of recording while actually making a screencast. - ss is very versatile in that regard, allowing to edit an existing video as well as delaying a video you are making. These terminal commands are included in Hizoka's excellent GUI Screencastor (Screen Beaver).