Every now and then during a commercial break, there’ll be a commercial that flashes on the screen for, like, a second. They look like tiny bits of full-length commercials. Are they put there on purpose by the advertiser, or are they a slip-up by the television network, not correctly judging the amount of time before the show goes back on the air?
I think but cannot be sure that the local affiliate or the cable network intended to replace one commercial with another, but slightly missed the timing.
It’s the local affiliate (or maybe cable provider) replacing the national ads in the national network feed (with local ads), but missing the timing slightly.
Yes, it’s this. Most TV stations use a computer to automatically insert commercials in a show and program them in ahead of time. The software will automatically insert a commercial into a scheduled program break, often on top of another commercial. It’s rare that there will be a person at a control panel manually inserting commercials into a show. Most channels are totally automated.
I saw what you did there. Well played. 
This is what is happening. Local TV usually gets it right. Cable TV messes it up. It all has to do with having the accurate time to the second - synchronizing clocks national and local.
It’s subliminal advertising. You may suddenly find yourself with a craving for Bloggo’s chocolate or desperate to go out and buy a new Hummer.
Especially noticeable here in the San Juan cable system since it will put a local ad (in PR-accent Spanish) on top of a network ad that starts in another language or accent.
That’s the likely explanation, but hard to believe it happens. My cable TV station syncs up to Internet time by accessing a network time server several times an hour. If it can’t reach the primary or secondary time server, I get an email about it (I could set it up to instantly text me). And this is a tiny local station.
Syncing time is one thing, syncing digital signal processing delays is another.
Compare your cell phone time to the second to your computer internet synchronized time to the second. The same?
Also cable TV has to synch with many different stations and these signals go over several different satellites. Local TV just needs to synch with New York and the signal is going through just one satellite.
Although it has to do with timing and synchronization, it has nothing to do with clock synchronization. Ad insertion technology doesn’t care about wall clock time.
As explained upthread, those flashes of commercial are the result timing errors in the insertion of local ads. The local ads are meant to overlay the “micro commercials” which are actually short bits of a whole commercial carried in the network feed. From a long-ago post:
SCTE 35 and few related standards that extend 35 allow frame-accurate insertion of digital audiovisual content in digital programming streams.
Some times I see shortened or truncated ads, and they often repeat 2x. What’s up with that?
Yes, the power of subliminal advertising has been proven beyond doubt.
Once, after a brief flash of an ad for a lawyers’ group, I was barely able to avoid the temptation to file a talcum powder lawsuit.
Blipverts. That is all.
That’s why I only watch Blank Reg’s Big Time TV.