Soon after the Political TV Ad Archive launched, Alvin Chang, an intrepid reporter for Vox, took it upon himself to watch every television ad that had bombarded Iowa television viewers, using the project’s data as his guide. By his count at that time, the 100 ads he watched were aired more than 45,000 times, which, if played back to back would account for 41 days worth of commercials.

He lived not only to tell the tale, but to write this exposition on what he saw. And his colleague, Emily Crockett, also noticed one ad that stuck out, which she wrote a separate piece about–this Bernie Sanders video which the campaign had posted on social media. Political TV Ad Archive data showed that it had aired more than 15 times. The video shows footage from a campaign event in which Bernie Sanders defends Hillary Clinton from what Crockett writes was “a bizarre sexist attack from Donald Trump.”

Clocking in at 1 minute, 28 seconds, this footage was longer than a typical ad, which tend to run in 15-, 30- or 60-second increments. (There are some notable exceptions, such as Marco Rubio’s 30-minute ad buy in Iowa the weekend before the caucus.)

After Vox posted the piece, Chang’s editor told him that Vox had heard from the Sanders campaign. That video, said the campaign, was not an ad. Chang asked Political TV Ad Archive staff to investigate.

We did, and what we found was fascinating, technologically speaking. To understand what happened, one must first understand the process by which the Political TV Ad Archive discovers and counts political TV ads, which is described in more detail here. There are a few ways this can happen, but in this case, a team member identified the ad on social media, and when viewed there clearly displays at the end the message “Paid for by Bernie 2016.”

Once logged into the Political TV Ad Archive system by Internet Archive researchers, an audio fingerprint of this ad was created, which, similar to a human fingerprint is unique. After that, the open source Duplitron system, described here, built by Dan Schultz, the architect of the Political TV Ad Archive, and started counting instances from the TV News library where this audio fingerprint appeared. This is where the “air count” statistic is created, and the graphic below shows that this particular video aired in a number of markets, including 11 times in San Francisco. However, when these airings were viewed individually, it became clear they came from instances where TV News broadcast were reporting on the Bernie Sanders footage, as opposed to being paid instances of an ad.

This was not entirely unexpected. We at the project are aware that our system counts instances of “earned media” along with “paid media,” and that at present we don’t have a way to distinguish between the two. In other words, if TV news broadcasters play an ad, whether it airs on TV as a paid ad or is posted on social media, the Political TV Ad Archive will capture that unique audio fingerprint and count it. Because earned media is itself an enormously interesting issue in this presidential campaign, we are working on ways to be able to distinguish these types of instances so that researchers, journalists, and the public will be able to trace the influence of political ads beyond paid airings.

However, this case was even more of an edge case than we would have expected. As it turned out, the TV news broadcasters were not necessarily airing footage that the Sanders campaign had posted on social media; instead, it appeared they were airing clips from footage of the actual campaign event. So this was not only not an example of a paid TV ad, but also not certainly the airing of “earned media” from a social media posting.

The good news from this episode is that, first, the audio fingerprinting tool used by the Political TV Ad Archive is so sensitive that it picked up these broadcast of the Sanders campaign event. And second, we now have valuable information to take into account as we strive to make the Political TV Ad Archive more responsive and sensitive to political advertising as it exists, as we like to say, “out in the wild.” Thanks to Vox for bringing this to our attention.