Well, technically it's on the internet now, but you get the idea.
Back when I was writing and producing Dharma and Greg, the only way to read my cards was to record each episode on a VCR and hit the "pause" button. This was not an easy task. The image wobbled like crazy making the tiny words of my weekly tomes very hard to see.
In video, sometimes the screen will show something briefly that you cannot tell what it is unless you play the video in slow motion or pause it. Often it turns out to be a joke or a Shout Out.
Unreadably Fast Text is a subtrope of this.
Also called a "Blink And You'll Miss It" moment.
(It's often good to link to pictures or actually describe what's seen when giving examples of this trope.)
Compare Easter Egg, Blipvert, and (when it happens in-story) Subliminal Seduction.
Thirty Seconds To Mars' Attack video, by way of superimposed writing and scribblings. Probably the only one in recorded history to use this to give a Shout Out to their fanbase and equate the lead singer to Satan within the same timespan.
Specifically invoked in the Matthew Good video for Weapon. Initially upset with what the video's director had done with it, Good took control of the project and inserted every-other-frame videos, very quick flashes of words, and actually lengthy diatribes that you have to pause to be able to read. The video won a Juno (the Canadian Grammy), but because Good boycotts the Junos, the original director accepted the award...despite not really making it in the first place.
The All-American Rejects' "Dirty Little Secret" video features people who's faces are hidden by little cards that admit their dirty little secret, such as suspecting that their fiancee isn't the One or exactly what happened at church camp...
Kennedy's "Mama Made Me a Pimp" features a split-second flash of a skull in the mirror, foreshadowing the protagonist getting killed in a knife fight by a rival pimp.
In the scene in Metal Gear Awesome where the player skips the long cutscene, slowing it down reveals some very strange drawings, and a screen with the handwritten text 'I wish people could see these drawings, I think they're pretty funny'.
"Really? You went to read this knowing it would lead you straight to hell? What the Ass-Puke is wrong with you? It's friggin' Hell! Fire, pain, the Devil, it's worth that to see what this said? That Guy With The Glasses was just kidding when he said you were going to Hell, but now that you've actually come back to pause it, we have no choice. You're going to Lem. It's a place like Hell but ten times worse. It's not written about in the Bible because every time some one tried writing about it, they'd cut their own head off. It's THAT bad. So I hope it was worth it, I hope it was worth pausing this video for that. See ya in Lem ya miserable piece of donkey rectum. En- friggin- joy!"
In Dead Fantasy Part V, the flickering in Tifa's flashback conceals text. Also, pausing at the moment right after Hayate knocks Tifa out will show a very, very brief image of a white materia in the middle of her back.
Also, all of Hayate's attacks and movements are animated - they just move so fast that they look like he's teleporting. You have to actually go through the video frame-by-frame to see what he's doing.
A fan ending to Botchamania episode 166 (which uses voice clips from NFL Blitz 2001) has a bunch of these. Interspersed with images of random wrestlers and Wrestle Crap moments, there are a few jokes written about them that can only be seen on the screen for a fraction of a second (example: the announcer calls out "Fat" while showing an image of Samoa Joe, and the caption above Joe's head reads "Damn you, Scott Steiner promos! And your unintentional hilarity!" note a reference to an interview from 2009 where Steiner calls Joe a "fat slob")
Pinisu-chan's essay in the first episode of Large Bagel begins with her trying to find out where she came from and if there are other Large Bagel's, only to change in the second paragraph to a Prince Of Bel Air parody.
In Paranoia Drift, an AMV that retells The Girl Who Leapt Through Time as delusions from Makoto's mind, there are a few frames at the beginning which read "This time while watching this video please remove all your emotional and logical effliction to this anime".
Five Second Films does a lot of "Blink and Your Miss It" jokes. For example in "Meanwhile, in Kansas", the headline of the newspaper at the end reads, "Don't Enter Politics. It Can Turn Your Daughter Gay!"
Used as foreshadowing in To Boldly Flee. When The Nostalgia Critic finds out the dialog he just spoke was written for him, we see the flash of script and realize that he didn't follow it to the letter. This sets up the gist of the next few scenes; that he's evolved and has taken control of his own character.
Community Channel has been doing this in her videos recently, because people kept pausing to read the fake webpages. Now they usually start with text that's relevant to the subject, cut off mid-sentence by "why do you guys pause the videos to read these" or something similar.
In Dragonball Z The Abridged Series, when Krillin uses a Solar Flare on Dodoria, the flash contains a shot of Freeza's head on the body of a black man showering.