NEW YORK (NYTIMES) - AT&T, one of the United States' biggest marketers, has yet to return to YouTube nearly a year after pulling its advertising from the platform because of concerns that it could appear alongside offensive material.

The company was among a wave of major marketers who paused their spending on YouTube in March 2017 after it was found that ads were appearing on videos promoting hate speech or terrorism and other disturbing content.

The Google-owned video service has since introduced a series of changes aimed at limiting the types of videos that can run ads, and most brands have resumed marketing on the platform.

But that has not been enough for AT&T, which wants YouTube to get "as close to zero tolerance for this issue as possible", Ms Fiona Carter, the company's chief brand officer, said in a recent interview.

"It became apparent to us as we worked through this that too much of the content our advertising could appear against was not brand safe - it was objectionable by any measure," Ms Carter said. "You really have an epiphany when you see some of that content."

She added: "Our findings are that no matter the algorithm or the filters or the formula that you currently apply, nothing beats human review."

AT&T believes that its dialogue with YouTube played a role in the platform's announcement last month (January) that humans will manually vet videos from channels that are part of Google Preferred, a designation applied to channels representing the top 5 per cent of content on YouTube that helps brands advertise on popular videos.

Over the past year, major marketers have been demanding more accountability from Google, Facebook and the rest of the digital advertising ecosystem, as they have come to the conclusion that the same algorithmic tools that allow unprecedented access to consumers can be used to spread misinformation, hate speech and harmful videos that target children.

On Monday (Feb 12), Mr Keith Weed, chief marketing officer of Unilever, called on tech companies to take greater responsibility for what appears on their sites and said his company would not invest in platforms "that do not protect our children or which create division in society and promote anger or hate".

"We've been talking about the digital supply chain for several years but what happened last year is it became a societal issue, a people issue," Mr Weed said in an interview after delivering remarks on eroding trust in tech companies at an industry conference in Palm Desert, California.

Mr Weed said that while he would pull dollars from the platforms "if something happened which was completely inappropriate for our brands or our business", he wanted to work with the companies to improve their sites.

Mr Brian Wieser, a media analyst at Pivotal Research, said marketers were clearly having an influence.

"If they said nothing then the only thing that would cause the platforms to act is the risk of government regulation," he said.

But Unilever, he said, was not taking an especially hard line with the tech firms as far as its advertising budget. "It's not like they set a threshold and said companies who don't do this lose their money specifically," he said.

Unilever, which owns brands like Ben & Jerry's and Dove, did not pull its marketing dollars from YouTube last year, saying at the time that the number of ads running with objectionable content was proportionally small and that it would use the moment to win new concessions from Google.

Mr Weed reiterated that position on Monday.

"What I'm talking about here is moving the conversation along," he said.

Unilever, for example, has been talking with YouTube about implementing more human screening of videos that include children to make sure that they are not being exploited.

"There is nothing we take more seriously than the trust and safety of our users, customers and partners, and we will continue to work to earn that trust every day," a Google spokesman said of Mr Weed's remarks.

Even though AT&T has not been spending money on YouTube ads in the past year, it has worked closely with the platform to improve its systems and is eager to have its ads again seen by YouTube's huge audience of teen and 20-something viewers.

YouTube has said that its manual reviews of Google Preferred channels would be complete by the end of March.

"We're very hopeful we can get back onto YouTube," Ms Carter said. "It delivers the scale we want but we had to roll up our sleeves and find that performance elsewhere."

AT&T spent more than US$1 billion (S$1.3 billion) on advertising in the US last year through September, while Unilever spent US$644 million, according to data from Kantar Media. AT&T was the sixth-biggest advertiser in the country during that period, Unilever was No. 16.

AT&T also said it would audit its programmatic ad spending in coming months, as it tries to better understand the process through which technology and automation place its online ads in front of consumers. That realm of advertising has drawn scrutiny from marketers in recent years amid reports that much of their spending, which is difficult to trace, is going to tech companies and agency fees rather than publishers.