The ability to film a politician while walking backward is a must. So is a bit of chutzpah: The job calls for walking uninvited into New Hampshire house parties until you are asked to leave. (That has not happened to Mr. Fielding — yet. ) He has gotten to know some of the Republican staff members, and they are beginning to know him.

Mr. Fielding is a descendent of sorts of S. R. Sidarth, the Democratic tracker who in 2006 captured Senator George Allen of Virginia calling him “macaca” — a term critics viewed as a racial slur. That incident helped destroy Mr. Allen’s re-election campaign and proved the power of the tracker. But Mr. Fielding is no mere volunteer. A veteran of campaigns in Louisiana and New Mexico, he is what American Bridge refers to as a “seasoned political operative.”

“I pay attention to what the important issues are,” Mr. Fielding said. “This is where the meat of the campaign is.”

Mr. Fielding’s efforts on July 4 produced no embarrassing moments. But officials at American Bridge insist that is not the point. Along with the video he uploaded, Mr. Fielding sent in detailed, time-coded “field reports” that will be entered into a searchable database and used to index the hours of video from the event.

If a Democratic group is ever looking for the image of Mr. Romney paying for a 25-cent lemonade with a $5 bill, it will know just where to go. If it wants a clip of Mr. Romney saying the president has made the economy worse, the archive will have one. Or if it needs Mr. Romney talking about World War II veterans, it will be able to find it.

“I can come up with the spin. I need the facts,” said Paul Begala, a former top adviser to President Bill Clinton and a senior strategist for Priorities USA Action, an outside group that is working to re-elect President Obama. Mr. Begala said American Bridge would help fuel his group’s ads. “Let’s go to the videotape!”