Compared with previous years, the number of Internet users who watched videos on YouTube and other Web sites has risen only slightly. The overall number crept to about 135 million in April from 132 million in May 2007, according to comScore, an online measurement firm.

But each of those users is watching far more video than before. ComScore reported that the average viewer watched 228 minutes of video in April, compared with 158 minutes in May 2007. One reason is that the videos people watch are becoming longer — the average viewer spent about 17 seconds more per video in April than in May 2007 — but most of the rise came from a spike in the number of videos that each person watched.