What is the likelihood of appearing on the TV show 'Border Security: America's Front Line' if I travel to the US?

The vast majority of the scenes aired on any of the Border Security shows (I've watched USA, Canada, Australia, and a few South American ones) take place in secondary. I'm a frequent traveler and I've been in secondary only twice in over 20 years. That's where a tiny fraction of travelers go after talking to an officer at a booth. Typically they have a good look through your luggage, ask more questions, look at paperwork in detail, call people such as the friend you're visiting, snoop through your phone, and so on. At least that's what you see on the show. The first time I was in secondary someone angrily asked me what I was doing there, and when I said someone told me to "go down there and turn left" they sighed, looked at my boarding pass and told me to leave. The second time (at US preclearance in Toronto) they made me wait, searched my carryon, threatened to take away my nexus card because I had caramels and had said I didn't have food, then let me proceed after about a half an hour delay.

Border Security do some "atmospheric" filming out at baggage claim and such. When they are doing so there are signs around. This news article includes this picture of the Canadian sign; the US one is probably similar. (Note: the Canadian series stopped filming in 2014 after accompanying CBSA officers out of the airport on a "raid".)

I have been in YVR and seen the signs but not seen the crew. The atmospheric filming generally never shows faces or voices of anyone other than the customs officers.

In secondary, I believe if you don't consent they show the footage with a blurred face and disguised voice. I could be wrong: perhaps those people only consented on the condition of the blurring and disguising, and there are others who don't consent and aren't broadcast.

Your chances are smaller than the chances of going to secondary, so I would say "very small." Literally millions of people pass through those airports every year and perhaps 10 or 12 people per airport per year appear on the show.

What is the likelihood ?

For all practical purposes it's 0. The US has about 80 million visitors each year. Maybe 100 or so appear on the show so it's almost literally "one in a million" (or 1.25 in a million to be exact).

The vast majority of people that appear on the show are doing something "unusual". If you are normal traveler with nothing that may trigger attention it's even lower than the number above.