A panel of online advertising and web executives at the OMMA conference in New York this week agreed that the most effective web video ads are 15 seconds in length or less.

The panel also suggested creating spots specifically for the web instead of attempting to re-purpose existing 30-second television spots, MediaPost reports. Advertisers must keep in mind the shorter attention spans of internet users, as well as developing ads that also allow consumers to click through to gain more product information, panel members said.

They also concluded that mobile advertising is still years away from being a viable platform and the U.S. market is three to four years behind Asia in mobile content development.