SOLVED - everything is working now. Thank you for your help.
Recap - in case it helps anyone else:
Problem: videos would not play after scraping, using Steven Selph's Scraper (optional package)
Replace the original video files with the converted video files.
My mistake: specifying the wrong option parameter for --to-ces
To test a video file will play: exit emulation station to the command line and try to run the video using omxplayer
$ omxplayer <path to video file>
Video files for testing are available here: