Pre-Caching

1. What is pre-caching?

  • Pre-caching in mobile is a common practice that allows the ad to be loaded in the background of the application and shown to the user once the app calls for the ad to be displayed. Pre-caching allows for an ad to be loaded off-screen as part of an application’s buffer to help provide a smooth user experience, and is a necessity on the supply side.

2. Which ad sizes / formats can publishers set pre-caching behavior for?

  • Interstitail and Rewarded Video ad format provide caching methods for developers.
  • Native assets are automatically cached ahead of showing when using AdPlacer. If using manual integration the publisher hands caching.

3. What is the expected behavior for a pre-cached ad?

  • For pre-caching of interstitials, there are two states:
    • “LOAD” (not visible) – when the ad and associated media assets are pre-loaded in the background
    • “SHOW” (visible) – when the ad becomes visible to the end user.
  • The MoPub SDK will fire impression trackers ONLY in the “SHOW” state. This is a cleared impression.
    • Impression trackers:
      • Server-to-server partners: Response nURL field
      • RTB 2.3: Response imptrackers field
      • MoPub Marketplace tracker if applicable
      • For more information on impression tracking, see Impression Tracking article.
    • ANY other pixels embedded in the ad markup will fire on “LOAD” and thus can create discrepancy with MoPub Marketplace impression trackers, Server-to-Server ‘nURL’, and RTB 2.3 ‘imptrackers’. (Does not apply to VAST video trackers)
    • Please note that an interstitial impression filled (for DSPs this is auction auction) by a demand partner and pre-cached/LOADED does not necessarily guarantee that ad will become visible and shown to the end user:
      • For example, a user may be playing a game when the interstitial is loaded in the background but quits out before the interstitial is shown .

4. What specifically is pre-cached?

Full screen:

  • Any and all assets required to render the creative (Javascript, images, video files, etc) will be pre-cached on ‘LOAD’.
  • Clickthrough destination landing pages are not pre-cached.

5. Does MoPub charge me for a pre-cached ad that is not shown to the user?

  • MoPub will ONLY charge and send the impression tracker (See #3 above) once the ad is shown to the user.

6. What is the average time elapsed between winning an auction and clearing an impression for pre-cached ad formats?

  • ~99% of interstitials (tablet & handset) are shown within 2.5 hours after the ad request.
  • ~99% of native ads are shown within 1.5 hours after the ad request.
  • The average time between auction and cleared impression will vary from publisher to publisher because it is dependent on publisher-side implementation.
  • Note: As of MoPub SDK 4.14, interstitial, rewarded, and native ad placer ads expire after 4 hours of being unused.

7. Do you have best practices for demand partners bidding on pre-cached inventory?

  • If the demand partner has strict time limits for latency between the response time stamp and the cleared impression timestamp they may be dropping impressions. We recommend accepting impression notifications up to an hour after the auction is won/filled, to ensure you are able to count the vast majority of winning / cleared impressions.

Last updated October 10, 2018

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