AUDIE CORNISH, HOST:
Now for some digital forensics. Here's House Speaker Nancy Pelosi speaking about Donald Trump. She was at the left-leaning Center for American Progress.
(SOUNDBITE OF ARCHIVED RECORDING)
NANCY PELOSI: Basically he's saying back to me, why would I work with you if you're investigating me? But the fact is something happened there.
CORNISH: Now here's the version that spread on social media - sounds a bit different.
(SOUNDBITE OF ARCHIVED RECORDING)
PELOSI: Basically he's saying back to me, why would I work with you if you're investigating me? But the fact is something happened there.
CORNISH: All right. One more time. Here's what Pelosi actually said.
(SOUNDBITE OF ARCHIVED RECORDING)
PELOSI: Basically he's saying back to me, why would I work with you if you're investigating me? But the fact is something happened there.
CORNISH: And here's what got around the Web.
(SOUNDBITE OF ARCHIVED RECORDING)
PELOSI: Basically he's saying back to me, why would I work with you if you're investigating me? But the fact is something happened there.
CORNISH: The real audio is about eight seconds long. The doctored version shared widely in some social media conservative circles is 11 seconds long. We want to bring in Hany Farid to talk about what's going on. He's a digital forensics expert at the University of California Berkeley. Welcome back to the program.
HANY FARID: It's good to be with you again.
CORNISH: So let's talk about the difference between these two audio clips. What do you hear?
FARID: This is a pretty low-tech fake. Essentially what happened is the video was slowed down a little bit, and the audio was tweaked to get the tone right. The result, though, is quite effective. It makes it sound like Speaker Pelosi is slurring her words.
CORNISH: But talk about how you're able to tell. I mean, how hard is it technically to manipulate a video in this way?
FARID: It's not that hard at all. It's actually relatively easy to do, to essentially slow down a video. So the average person would be able to do this. The detection is interesting. In this case, it was actually relatively easy because you can go to C-SPAN and you can look at the original. And you can see that it's not slowed down by a small amount. It's about 75% - as you said, eight seconds to around 11 or 12 seconds.
When I first saw the video, it seemed to me obviously fake because it just was so exaggerated in the slurring of the words. And it looked to me like the video had been slowed down. Her facial expressions weren't moving properly. So I was pretty sure it was a fake. But once you saw the original C-SPAN video, then it's very easy to determine what happened.
CORNISH: At the same time, you had high-profile supporters of the president - his personal lawyer, Rudy Giuliani, tweeted a link to the video with the message, what is wrong with Nancy Pelosi? He later deleted that tweet. What does it mean when we see people spreading it like this?
FARID: Yeah. So there's the sort of the rub in all of this is that the fake content is not in and of itself perhaps the biggest problem. I think the biggest problem is the ability to amplify that and spread that around the world almost instantaneously through social media and then, of course, have that being amplified by the president, the White House and the people who work for him.
And so therein lies, I think, sort of the danger here is that it's not just a technological problem from the creation of the fake. It's a technological problem from the distribution. And then, of course, it's a very human problem - all of us consuming that, believing it too readily and then spreading it even further.
CORNISH: YouTube took down the altered video of Pelosi, Facebook has not. What role should these companies have in approaching this problem?
FARID: I think this is going to be one of the defining issues of the next few years for us is, how do you take these private companies and have them take on huge, massive societal responsibilities to the tune of, by the way, 500 hours of YouTube video uploaded a minute? And this video is also incredibly challenging. So when we were dealing with the New Zealand video of the horrific violence, that was a clear-cut case. There was no place for that video online.
This video is more interesting. It's not a fundamentally bad video. Satire is fine. Comedy is fine. But when it is put in the context of fake news and trying to disparage our politicians or individuals, well, then it's a more complex issue that we have to deal with. So it's not just a technical issue. It's also a policy issue in how we think about balancing speech and an open and free Internet.
CORNISH: Hany Farid is a computer science professor and digital forensics expert at the University of California Berkeley. Thank you for speaking with us.
FARID: Good to be here. Thank you. Transcript provided by NPR, Copyright NPR.