The video, which shows Pelosi's onstage comments at the Center for American Progress on Wednesday, has been slowed down, which makes her words seem slurred.
Although the video has been removed by YouTube, copies of it were still circulating on Facebook and Twitter on Thursday evening.
"By my calculation, the altered video has been slowed by almost 75% introducing a significant distortion in her speech," Hany Farid, a professor at UC Berkeley and expert in digital forensics and image analysis, told CNN.
A Facebook representative told CNN on Thursday that the Pelosi video had been referred to the company's third-party fact checkers for review, but that as of early evening on Thursday none of the third-party fact checkers had rated the video.
The representative explained that Facebook does not have a policy that stipulates information people publish on Facebook must be true. Among the steps Facebook takes to tackle the spread of false information is demoting it in the Facebook News Feed so it is seen by fewer users, the representative said.
If Facebook receives from its third-party fact checkers an indication that the Pelosi video was misleading, it would significantly reduce the distribution of the video on Facebook, the representative added.
YouTube, owned by Google, removed the video, its spokesperson told CNN.
"YouTube has clear policies that outline what content is not acceptable to post and we remove videos violating these policies when flagged to us. These videos violated our policies and have been removed," the spokesperson said.
The video did not appear prominently in YouTube search and YouTube's recommendations, the spokesperson said.
A Twitter spokesperson said the company had nothing to share about the video.
On Thursday night, Fox Business' 7 p.m. ET show featured a segment in which panelists speculated about Pelosi's health and competence on the basis of an edited clip of her recent speech. Trump subsequently tweeted the clip with a disparaging comment.
A short time later, Trump's attorney Rudy Giuliani also tweeted ̵
But Farid said the less sophisticated editing of the Pelosi video shows that peddlers of misinformation do not need high tech.
"It is striking that such a simple manipulation can be so effective and believable, to some," Farid told CNN. "While I think that deep-fake technology poses a real threat, this type of low-tech fake shows that there is a big threat of misinformation campaigns – too many of us are willing to believe the worst in people we disagree with. "