Astute television viewers know that cable networks have long crunched opening or closing credits on reruns to squeeze more time for ads into an hourlong slot. No harm, no foul, we say.

But now comes disturbing word of cable mandarins tinkering with television classics. TBS and other cable channels use computer compression technology to subtly speed up some shows, the Wall Street Journal reports.

And viewers have noticed. Author Stephen Cox, for instance, detected that the voices of the Munchkins in “The Wizard of Oz” were slightly raised, he told the Journal. “It was astounding to me.”

And to us. TBS didn’t stop at the exalted Oz. It has sped up classic “Seinfeld” reruns and other shows. Viacom’s TV Land channel has accelerated “Friends” reruns, so it takes slightly less time for Ross and Rachel to get together and break up and get together and …

What to make of this?

In general, we applaud the acceleration of American life. We want our Starbucks latte to be delivered even faster.

We won’t wait more than a few minutes for a restaurant table.

Our favorite words:  Express lane.

We firmly believe there should be a speed lane on sidewalks for brisk walkers.

If election campaigns were whittled to weeks, not months or years, who would complain?

There are many TV programs we could rattle off — starting with the entire “Bachelor” or “Bachelorette” series and a passel of lame-but-somehow-popular comedies like “Two Broke Girls” — that would be improved if they were sped way up. An episode of “The Big Bang Theory” mercifully should take seven minutes, tops. We wouldn’t raise a typing finger if “Two and a Half Men” clocked in at One and a Quarter Men. Or fewer.

However, tampering with a classic movie on television, sneakily adding an octave to the Munchkins’ voices, is a maneuver that we cannot endorse.

Because what starts on an egregiously padded series (“American Idol” reruns?) can easily be deployed to slice precious moments from, say, repeats of the sublime BBC series “Sherlock” or the delightful “The Mindy Project.” And what starts as a few shaved seconds can easily snowball into bigger chunks of time, leading to stellar TV episodes that hurtle along at Keystone Kops speed.

There’s another practical reason to crush this trend before it gains more momentum: We already have enough trouble following the convoluted plot twists and faster-talking explanations of “Elementary” or the British accents in “Downton Abbey.” If you accelerate those shows, there’s even less time for the brain to absorb and savor every moment. We need a chance to catch our breath and mull the breakneck plot revelations in an intense episode of “Elementary.”

No, cable mandarins, we will not accept the Alvin-and-the-Chipmunking of classic reruns. We demand to savor every last second of these shows, even if we’ve seen them a dozen times. Hands off, or else. We know how to use that remote.