Compressing an .MP4 causes a transcoding process failure in FFMPEG. The MP4 was created using the PowerPoint 2016 Screen Recording tool.
I created an .MP4 using the default configuration in PowerPoint 2016. When the file is compressed using FFMPEG, the process fails without creating a new file.
Other .MP4's work fine with FFMPEG. I believe the problem is with the .mp4 generated by PowerPoint 2016.