WSJ wrote this week that advertising revenue from YouTube is likely to total $200 million this year and thus fall short of Google's expectations.
Google also has significantly cut the number of YouTube clips it will sell ads against, so as not to sell them against videos that may violate copyrights, the newspaper said, citing one source.
Google and YouTube are being sued for copyright infringement in two cases involving YouTube and a second suit where the lead plaintiff is the English
The Internet advertising leader only sells ads against clips posted on YouTube that are approved by media companies or other partners, which represent just 4 percent of the clips on YouTube, a source said.
Much of the remainder are user-generated clips where rights are uncertain and where advertisers may be nervous about placing their ads against videos of unknown origin.
Google also plans accepting "preroll" and "postroll" ads to run before or after some YouTube clips. These ad formats, while considered effective with advertisers are often unpopular with Web users, one of the sources said.
The paper writes Google North American ad sales chief Tim Armstrong and his colleagues scrutinized YouTube's ad sales system and found 105 problems.