As the first presidential primary of the YouTube era nears its end, wonks may wonder which Web spots -- from both candidates and third parties -- have had the most impact on voters. The influence of online videos can be difficult to measure, but some independent developers have created tools that aim to contextualize Web video-watching trends and compare the resonance of different releases.

One such application, TimeTube, sorts YouTube videos based on a particular search term and charts them onto a timeline according to viewership. The more times the video has been watched, the larger its thumbnail appears onscreen.

Querying the three presidential candidates reveals that many of the most-watched videos are attack ads and embarrassing clips. For example, a satirical song criticizing John McCain's statements on Iraq and Iran is given prominence on his timeline because of its more than 1.6 million views. (His campaign's most-watched official Web release -- a 16-second clip of Bill Clinton praising McCain -- garnered fewer than a quarter as many hits.)

Searching for other politicians yields similarly negative results. "I'm particularly fond of Eliot Spitzer's TimeTube, which provides a nice contrast between his cheery political ads and the infamous Client Number 9 debacle," Jason Kincaid wrote at TechCrunch. While Kincaid questions the value of indexing videos based on when they were uploaded -- rather than the actual date of the footage -- TimeTube's system has the advantage of showing how old video clips are sometimes resurrected during a campaign, as when CBS excavated footage in response to Hillary Rodham Clinton's inaccurate recollection of a 1996 visit to Bosnia.

Another aggregate tool, Vizband, gives a more impressionistic sense of a candidate's online image by generating a mosaic of video screenshots that come up when the candidate's name is searched. The picture painted of Barack Obama, for example, is a little sunnier than the other candidates, as the collage produced by searching his name includes multiple appearances of the "Yes We Can" video by Black Eyed Peas front man Will.I.Am. This clip, which was viewed more than 17 million times, recently won a Webby.

But some question the accuracy of the traffic figures on which these mash-ups are based. A Wired blog recently noted a debate over the number of views an anti-Obama video received at Eyeblast.tv, a conservative group's video-sharing hub. While Eyeblast.tv producer Daniel Glover (formerly of National Journal Group), said it's been viewed over one million times, Tech President's Joshua Levy called the number "highly suspicious."

Despite the debate over metrics, it's clear that the overall viewership of online video is increasing. Online video-watching in March was 64 percent higher than it was last year, according to one research group. Americans watched 11.5 billion online videos that month, some 4.3 billion of which were hosted by YouTube. As the political impact of online video and advertising continues to grow, so too will politicos' need for reliable tools to tell them what's hitting home and what's shaping public perception of candidates on the Web.