Multi-format impressions with banner, video, audio, and native in one imp

One imp, several offers

The specification lets the publisher offer one format, which is the usual case, or mix them. The presence of a media object is the offer. Everything else on the Imp applies to every format at once: imp.bidfloor, imp.pmp, imp.secure, imp.instl, and imp.tagid.

{
  "id": "c8d3e1f0-7a2b-4c5d-9e6f-0a1b2c3d4e5f",
  "at": 1,
  "tmax": 300,
  "cur": ["USD"],
  "imp": [
    {
      "id": "1",
      "tagid": "article-mid-1",
      "secure": 1,
      "bidfloor": 1.5,
      "bidfloorcur": "USD",
      "banner": {
        "format": [{ "w": 300, "h": 250 }, { "w": 336, "h": 280 }]
      },
      "video": {
        "mimes": ["video/mp4"],
        "protocols": [7, 11, 13],
        "plcmt": 4,
        "w": 300,
        "h": 250,
        "minduration": 6,
        "maxduration": 30,
        "durfloors": [
          { "maxdur": 15, "bidfloor": 6.0 },
          { "mindur": 16, "bidfloor": 9.0 }
        ]
      },
      "native": {
        "ver": "1.2",
        "request": "{\"ver\":\"1.2\",\"assets\":[{\"id\":1,\"required\":1,\"title\":{\"len\":90}},{\"id\":2,\"required\":1,\"img\":{\"type\":3,\"wmin\":300,\"hmin\":250}}]}"
      }
    }
  ],
  "site": {
    "id": "site-4410",
    "domain": "trailguide.example",
    "page": "https://trailguide.example/gear/winter-boots",
    "publisher": { "id": "pub-208" }
  }
}

This in-article slot takes a 300x250 or 336x280 banner, a standalone outstream video (plcmt 4, No Content/Standalone) of 6 to 30 seconds, or a native ad with a title and a main image. The native request is a JSON string inside the JSON, as the native request post explains.

Banner objects inside Video.companionad are not a separate banner offer. They describe companion ads that travel with the VAST response. An imp is a banner offer only when imp.banner itself is present.

mtype tells the exchange which offer you took

{
  "id": "c8d3e1f0-7a2b-4c5d-9e6f-0a1b2c3d4e5f",
  "cur": "USD",
  "seatbid": [
    {
      "seat": "agency-977",
      "bid": [
        {
          "id": "b-31",
          "impid": "1",
          "price": 7.2,
          "mtype": 2,
          "dur": 15,
          "protocol": 13,
          "adm": "<VAST version=\"4.2\">...</VAST>",
          "adomain": ["northpeak-outfitters.com"],
          "crid": "cr-v-77",
          "w": 300,
          "h": 250
        }
      ]
    }
  ]
}

The bid takes the video offer: mtype 2, VAST 4.2 markup, and a 15-second creative in Bid.dur. Before 2.6 there was no mtype, and an exchange had to work out the format by inspecting the markup. Wrappers still differ on what they do without it. The Prebid.js ortbConverter discards a bid with no mtype unless the adapter has set the media type itself. Prebid Server adapters label each bid with a media type in code, and the server returns it as seatbid[].bid[].ext.prebid.type.

Floors per format

imp.bidfloor is a single floor for every offered format, in imp.bidfloorcur (default USD). That currency also applies to the other floors inside the Imp. OpenRTB has no banner-only or native-only floor field. Video and audio have two ways to vary the floor:

In the example, a banner or native bid must clear 1.50. A video bid of up to 15 seconds must clear 6.00 and a longer one 9.00, through the DurFloors.bidfloor entries. A creative outside every range falls back to the Imp floor. The specification puts no constraints on the ranges and leaves overlaps for buyer and seller to settle. A bidder that reads only imp.bidfloor will price a 30-second video against 1.50 when the seller asked for 9.00. The floors reference covers currencies and deal floors.

Prebid.js fills the gap with an extension. When its Price Floors module resolves different floors per media type, it writes them to imp.banner.ext.bidfloor, imp.video.ext.bidfloor, and imp.native.ext.bidfloor, and per size to imp.banner.format[].ext.bidfloor, each with an ext.bidfloorcur. These are not OpenRTB fields. A bidder has to read them on purpose.

How exchanges validate a multi-format bid

OpenRTB does not rank formats. Bids in different formats for the same imp compete in one auction, and any preference for video over banner is exchange or publisher policy. What an exchange can check is whether the bid fits the offer it claims:

• Bid.impid matches an imp, and mtype names a media object on that imp. RTBlint reports a miss as openrtb.bid.mtype_not_offered.
• The markup in Bid.adm matches mtype: openrtb.bid.adm.markup_type_mismatch. Native markup that is not JSON gets its own code, openrtb.bid.adm.native_not_json.
• The markup matches some format the imp offered, even when mtype is missing or wrong: openrtb.bid.adm.media_type_mismatch.
• A banner's Bid.w and Bid.h fit banner.format, and a video's duration fits the duration limits. The loss reasons are 203 for a size and 204 for the wrong creative format.
• The price clears the floor for the format and duration the bid chose.

A bid with adm and no mtype on a 2.6 request draws the warning openrtb.bid.mtype_missing.

Bidders and wrappers that handle one format

Not every bidder accepts every offer. Prebid Server (Go) wraps each adapter in a filter driven by the bidder's info file. Media types the bidder does not support for site, app, or DOOH traffic are removed from the imp before the adapter sees it, and an imp with nothing left is dropped. A bidder whose info file sets multiformat-supported: false receives one media type per imp, chosen by ext.prebid.biddercontrols.{bidder}.prefmtype. Without a preferred type, the server removes the imp for that bidder. The Prebid Server extensions guide covers the rest of the request.

In Prebid.js, an ad unit whose mediaTypes lists banner, video, and native becomes one imp with all three objects when the adapter uses the shared ortbConverter. An adapter can pass a single mediaType in the converter context to build a one-format imp instead. The Prebid.js ortb2 guide walks through the converter.

Mistakes that get multi-format bids rejected

• A constant mtype. One code path hard-codes 1 and then returns VAST on a video win.
• A size the imp never listed. A 728x90 banner against an imp that offered 300x250 and 336x280 fails the size check, whatever the price.
• Video priced against the Imp floor. The bid ignores durfloors and lands under the floor for its duration.
• A creative outside the duration limits. A 45-second spot against a maxduration of 30 does not fit the video offer.
• Treating companions as a banner offer. A banner bid on an imp whose only Banner objects sit in video.companionad answers an offer nobody made.
• Native markup sent as HTML. mtype 4 promises the JSON response the native request described.

To see a format check fail, load the mismatched pair sample: it returns banner markup with mtype 1 against a video-only imp.

Sources

• OpenRTB 2.6 specification: Object: Imp, Banner, Video, Audio, Native, Deal, DurFloors, and Bid
• Prebid.js ortbConverter README (mtype handling and per-format floors)
• Prebid.js Price Floors module source (ext.bidfloor per media type)
• Prebid Server (Go) media type and multi-format filtering

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