Google Public Policy Manager Verity Harding said that about 300 hours of video material is being uploaded to YouTube every minute.
She told a European Parliament meeting of the ALDE liberal group on a counter-terrorism action plan that "to pre-screen those videos before they are uploaded would be like screening a phone call before it's made."
The European Union's counter-terror chief believes it's time to help companies to contain the security risk by having experts from member states flagging terror-related content.
"We have to help them, and refer to them, and signal content," Gilles De Kerchove said. "Each member state should have a unit with people trained to do that."
On YouTube, users can highlight problem videos and have them reviewed by a member of staff.
When a Scotland Yard unit recently told Google about material that did not comply with the company's own guidelines, De Kerchove said 93 percent of that content was removed. But when individuals flag up problems only a third of it is taken down.
Detecting violent, extreme and racist material is a mammoth task. But concerted, targeted warnings from organized groups work best.
"There are community groups and others who do this on a larger scale and they're incredibly helpful to us," Harding said.
Despite the serious threat posed by extreme and violent videos, neither the big Internet companies nor the European Union appear willing to take on a legal battle to enforce their removal.
"We can contemplate legislation but I suspect it would be an awfully monumental exercise," De Kerchove said.
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