On my laptop I have only ever had Full Motion Video 1.4 installed, and I installed it after upgrading to ArcGIS Desktop 10.6.
Consequently, when I tried running the Video Multiplexer tool, I was surprised to see it give a message that included "Full Motion Video GP Tools v1.3.2 for ArcGIS Desktop 10.5".
Does the error below suggest that this tool has not been updated for ArcGIS Desktop 10.6?
Executing: VideoMultiplexer "C:\Temp\test.MP4" "C:\Temp\test.csv" "C:\Temp\test_output.mp4" # # # # "Use input video bit rate" -1
Start Time: Wed Feb 28 20:12:10 2018
Full Motion Video GP Tools v1.3.2 for ArcGIS Desktop 10.5
Output video bit rate: 8 mbps
Execute(): Object reference not set to an instance of an object.
Failed to execute (VideoMultiplexer).
Failed at Wed Feb 28 20:12:14 2018 (Elapsed Time: 4.16 seconds)