Prebid

Prebid is the open-source library that runs most header bidding auctions on the open web. Prebid.js (the browser version) launched in 2015 and now ships on a majority of large publisher sites; Prebid Server (the server-side variant) handles the same parallel-SSP auction logic in a single back-end call, which reduces page-load weight and centralizes SSP integration.

On CTV, "Prebid Video" extends the same model, typically run server-side via Prebid Server because client-side JS is brittle in ad-pod video players. On DOOH, Prebid hasn't fully landed yet; most DOOH SSPs run proprietary auction logic. The Trillboards supply layer runs a Prebid-compatible parallel auction internally and exposes the result to upstream SSPs.

Prebid's value isn't the auction code per se, that's a few hundred lines. The value is the SSP adapter ecosystem: 200+ adapters for SSPs and exchanges, all maintained in one repo against a stable interface contract. A publisher (or DOOH supply network) gets parity with the rest of the market by depending on Prebid.

For DOOH-curious readers: the analog of "Prebid.js in the page header" is "Prebid Server called by the ad-pod orchestrator before the loop starts". Same model, server-side. SPO on the buy side is mechanically dependent on Prebid-style parallel auctions; without them, there's no path to optimize.