New-media research firm eMarketer revised its online-video ad spending projections downward, saying advertisers will spend $505 million this year. That’s only about a third of the firm’s previous prediction of $1.4 billion in ad spending.

The firm said the drop comes from a change in methodology. eMarketer said the lowered estimate is still an increase of 56% from last year.

Online video advertising represents about 2% of total Internet ad dollars and less than 1% of TV ad spending in 2008, eMarketer said.

The firm said about 67% of U.S. online users will watch video ads at least once a month this year.