Google Inc.'s YouTube, the most popular online video site, has started a short-film competition sponsored by Hewlett-Packard Co. to help boost advertising sales.

Entries must be two to seven minutes long and be submitted between Oct. 7 and Nov. 9, YouTube, based in San Bruno, Calif., said Monday in a statement. To support Hewlett-Packard's latest ad campaign, the films must include the line "What do you have to say?"

Google, which bought YouTube for $1.65 billion last year, accounted for 27 percent of all Internet videos watched in July, according to researcher ComScore Inc. To capitalize on that growth, Google, based in Mountain View, Calif., started showing ads from companies such as Warner Music Group Corp. and the Twentieth Century Fox film studio in August.

YouTube users will vote on the entries. The winner will spend nine days at an international film festival, have a meeting with Fox's Searchlight studio, and receive $5,000.