Gripes over autoplay videos scrolling on Facebook and Twitter just got deadly serious.

Automatic video-playback features on Facebook and Twitter sparked outrage Wednesday, as they effectively forced legions of unsuspecting users to watch grisly footage of the on-air murders of a Virginia TV reporter and her cameraman.

The video was shared 500 times on Facebook before it was quickly taken down, according to one tweeter.

As complaints about the video grew, some tech bloggers hastily posted instructions on how to disable the feature, which begins playing videos automatically as soon as they emerge on a user’s scrolling news feed.

Facebook, which introduced autoplay in late 2013, has touted the format’s success as it escalates a high-stakes battle with Google’s YouTube site.

In June, Facebook said the feature had helped boost its video views to 4 billion a day from 1 billion last year.

Facebook’s revenue stream from the videos is likely to grow, as well. But a large number of users disabling autoplay could cut into revenues — at least in the short term.

“Twitter and Facebook autoplay videos made me witness the murder of someone from multiple angles today,” tweeted Tom Warren, senior editor at tech blog The Verge. “Good job technology.”

In a terse statement, Facebook said it had deleted the suspect’s profile for “violating our community standards.”

Looking to stem the PR damage, a Twitter spokesman pointed to settings that allow users to put warning messages on content marked as “possibly sensitive.”

The spokesman didn’t respond when asked in an email by The Post about disturbing content that was unmarked.

To be sure, Facebook and Twitter have scrambled to take down inflammatory videos before, including footage of ISIS executions earlier this year.

Facebook, meanwhile, has created surprisingly effective algorithms that prevent improper posts of everything from first-run TV shows to pornography videos.

But the viral spread of fresh murder footage, unaccompanied by warnings to viewers, takes the issue to a new level — and presents a new technological challenge, said William de Lannoy of Noble People, a New York marketing firm.

“To prevent this, you would have needed a computer that can take a dark, blurry thing and somehow figure out it’s a gun with someone holding the trigger,” de Lannoy said.

“There’s a risk it could slow down the Facebook video juggernaut that’s happening now.”

Autoplay ads — which have been pitched as a less annoying alternative to regular video ads because they default to silent mode and stop and start when scrolled over — are likely to survive this week’s tragedy, industry execs said.

That’s because ads can be vetted before airing on social networks. Any new clampdown on unvetted content wouldn’t stem their flow.

“Platforms will likely make adjustments, but advertisers will probably continue to use them,” says Mitchell Reichgut, CEO of Jun Group, a New York ad firm.

Warning: Graphic content