Example VAST Key concepts Benefits Enabling How it works VAST wrapper behavior Metrics and monitoring ADS event changes See also

Ad buffet

The Interactive Advertising Bureau (IAB) Video Ad Serving Template (VAST) specification defines ad pods and ad buffet. This mechanism supports ordered ad insertion with automatic fallback on ad insertion failure. In an ad pod, sequenced ads play in order. Standalone ads serve as a buffet from which MediaTailor selects replacement ads when a sequenced ad fails.

AWS Elemental MediaTailor supports this specification through the AdSequencingMode setting in the AdDecisionServerConfiguration of the PlaybackConfiguration. When set to FOLLOW_AD_SEQUENCE, MediaTailor inserts sequenced ads in order and uses standalone ads only as substitutes when a sequenced ad fails to insert.

Example VAST response

The following example shows a VAST response that contains sequenced ads and standalone ads:


<VAST>
  <Ad sequence="1" id="sequencedAd1">...</Ad>    <!-- Sequenced Ad 1 -->
  <Ad sequence="2" id="sequencedAd2">...</Ad>    <!-- Sequenced Ad 2 -->
  <Ad id="standAloneAd1">...</Ad>                <!-- Standalone Ad 1 -->
  <Ad id="standAloneAd2">...</Ad>                <!-- Standalone Ad 2 -->
  <Ad id="standAloneAd3">...</Ad>                <!-- Standalone Ad 3 -->
</VAST>

In this example, the two sequenced ads form an ad pod. The three standalone ads form the ad buffet. Together they constitute one buffet group. If sequencedAd1 fails, MediaTailor first attempts to replace it with an eligible standalone ad from the same buffet group. If no eligible standalone ad is available in that group, MediaTailor selects from standalone ads in other buffet groups.

The following diagram shows a VAST response with an ad pod (sequenced ads) and an ad buffet (standalone ads) that together form a buffet group.

Diagram of a VAST response with an ad pod (two sequenced ads) and an ad buffet (three standalone ads) forming one buffet group.

Key concepts

The following terms describe the core concepts of ad buffet:

Sequenced ads – Ads with a sequence attribute in the <Ad> element. These form an ordered ad pod and are inserted in increasing sequence order.
Standalone (buffet) ads – Ads without a sequence attribute. These are used only as substitutes when a sequenced ad fails to insert.
Buffet group – MediaTailor pairs an ad pod with its standalone ads within a single VAST response. When a sequenced ad is a wrapper, its redirected VAST forms its own independent buffet group. When replacing a failed sequenced ad, MediaTailor prioritizes standalone ads from the same buffet group. If no eligible standalone ad exists in the same buffet group, MediaTailor falls back to standalone ads from other buffet groups.

Note

sequence refers to the <Ad> element-level attribute, not the sequence attribute found in the <Creative> element.

Benefits of ad buffet

Without ad buffet, MediaTailor treats all ads identically, which can result in the following issues:

VOD – Standalone ads are inserted even when no failures occur, disrupting agreed-upon ad break positions and overfilling ad breaks.
Live – Lower-revenue standalone ads can be inserted before sequenced ads and occupy avail duration, leaving no room for higher-revenue sequenced ads.

With ad buffet enabled, MediaTailor inserts only sequenced ads and uses standalone ads only as substitutes when a sequenced ad fails to insert. This ensures that the highest-revenue ads are played first.

Warning

If your Ad Decision Server (ADS) response does not contain any sequenced ads (no <Ad> element has a sequence attribute), enabling ad buffet results in no ad insertion.

Enabling ad buffet

Ad buffet is an opt-in feature that you configure for each playback configuration using the PutPlaybackConfiguration API.

AdSequencingMode values

The following table describes the available AdSequencingMode values.

Value	Description
`IGNORE_AD_SEQUENCE` (default)	MediaTailor inserts ads in the order they appear in the VAST response, regardless of sequence attributes.
`FOLLOW_AD_SEQUENCE`	MediaTailor inserts sequenced ads in order for both live and VOD workflows. Failed sequenced ads are replaced with standalone ads.
`FOLLOW_AD_SEQUENCE_ONLY_LIVE`	Ad buffet behavior is enabled for live workflows only.
`FOLLOW_AD_SEQUENCE_ONLY_VOD`	Ad buffet behavior is enabled for VOD workflows only.

Note

When you enable ad buffet, MediaTailor respects the Wrapper.fallbackOnNoAd and Wrapper.allowMultipleAds attributes.

Midroll configuration

The following example enables ad buffet for both live and VOD workflows:


{
    "PlaybackConfiguration": {
        "AdDecisionServerConfiguration": {
            "VastResponse": {
                "AdSequencingMode": "FOLLOW_AD_SEQUENCE"
            }
        }
    }
}

The following example enables ad buffet for live workflows only:


{
    "PlaybackConfiguration": {
        "AdDecisionServerConfiguration": {
            "VastResponse": {
                "AdSequencingMode": "FOLLOW_AD_SEQUENCE_ONLY_LIVE"
            }
        }
    }
}

The following example enables ad buffet for VOD workflows only:


{
    "PlaybackConfiguration": {
        "AdDecisionServerConfiguration": {
            "VastResponse": {
                "AdSequencingMode": "FOLLOW_AD_SEQUENCE_ONLY_VOD"
            }
        }
    }
}

Live preroll configuration

The following example enables ad buffet for live preroll ads:


{
    "PlaybackConfiguration": {
        "LivePrerollConfiguration": {
            "AdDecisionServerConfiguration": {
                "VastResponse": {
                    "AdSequencingMode": "FOLLOW_AD_SEQUENCE"
                }
            }
        }
    }
}

Note

LivePrerollConfiguration only supports FOLLOW_AD_SEQUENCE and IGNORE_AD_SEQUENCE. Configure ad buffet for VOD preroll through the midroll configuration.

How ad buffet works

Ad replacement conditions

If a sequenced ad encounters one of the following failure cases, MediaTailor attempts to replace the sequenced ad with an eligible standalone ad from the same buffet group. If no standalone ad is available in the same buffet group, MediaTailor uses a standalone ad from other buffet groups, if available.

Failure case	Description
VAST parse failure	A sequenced ad fails to parse because of missing required VAST elements (for example, `MediaFiles`, `Creatives`, or `Impression` are missing, or `MediaFile` or `VASTAdTagURI` is invalid).
VAST wrapper resolution failure	A redirect times out, fails, or returns an empty response.
VPAID ad dropped	A sequenced ad is VPAID and the session uses server-side reporting or has no slate configured.
Ad transcode not ready	A sequenced ad's transcode status is not SUCCESS (for example, IN_PROGRESS or ERROR).
Avail duration exceeded	A sequenced ad's duration exceeds the remaining avail duration (live workflows).

Standalone ad eligibility

To be eligible as a replacement, a standalone ad must meet the following criteria:

Not be a VPAID ad
Have a completed transcode
Have a duration that fits within the remaining avail duration

Standalone ad selection

When a sequenced ad fails, MediaTailor selects a replacement from eligible standalone ads using the following priority:

Same buffet group first – MediaTailor prefers standalone ads from the failed ad's own buffet group.
Other buffet groups – Used only if no eligible ad exists in the same buffet group.

If no eligible standalone ad is found, the position is unfilled and the appropriate SkippedReason is emitted.

VAST wrapper behavior

The handling of a Wrapper redirect response by MediaTailor depends on the value of two Wrapper variables: Wrapper.fallbackOnNoAd and Wrapper.allowMultipleAds.

fallbackOnNoAd takes effect when the redirect response is empty, times out, or an error occurs during the ADS request.
allowMultipleAds takes effect if the ADS response contains one or more ads.

Empty VAST, request error, or request timeout

The following table describes MediaTailor behavior when the redirect response is empty, times out, or an error occurs.

fallbackOnNoAd	MediaTailor behavior
`true` (default)	MediaTailor selects a standalone ad to replace the failed wrapper, preferring the same buffet group. If no eligible same-group ad is available, MediaTailor selects from other buffet groups.
`false`	MediaTailor drops the ad position and moves on to the next ad in the pod. No replacement occurs.

Example fallbackOnNoAd=true (redirect fails)

Parent VAST:


<VAST>
  <Ad sequence="1" id="seqAd1">...</Ad>
  <Ad sequence="2">
    <Wrapper fallbackOnNoAd="true">
      <VASTAdTagURI>https://ads.example.com/vast</VASTAdTagURI>
    </Wrapper>
  </Ad>
  <Ad id="standAloneAd1">...</Ad>
  <Ad id="standAloneAd2">...</Ad>
</VAST>

Wrapper redirect response: Empty VAST, times out, or errors.

Resolved VAST:


<VAST>
  <Ad sequence="1" id="seqAd1">...</Ad>
  <!-- standAloneAd1 replaced failed Wrapper Ad and now has the Wrapper's sequence (2) -->
  <Ad sequence="2" id="standAloneAd1">...</Ad>
  <Ad id="standAloneAd2">...</Ad>
</VAST>

Playback order:

seqAd1
standAloneAd1

Example fallbackOnNoAd=false (redirect fails)

Parent VAST:


<VAST>
  <Ad sequence="1" id="seqAd1">...</Ad>
  <Ad sequence="2">
    <Wrapper fallbackOnNoAd="false">
      <VASTAdTagURI>https://ads.example.com/vast</VASTAdTagURI>
    </Wrapper>
  </Ad>
  <Ad id="standAloneAd1">...</Ad>
  <Ad id="standAloneAd2">...</Ad>
</VAST>

Wrapper redirect response: Empty VAST, times out, or errors.

Resolved VAST:


<VAST>
  <Ad sequence="1" id="seqAd1">...</Ad>
  <!-- sequence 2 is not replaced -->
  <Ad id="standAloneAd1">...</Ad>
  <Ad id="standAloneAd2">...</Ad>
</VAST>

Playback order:

seqAd1

Response contains one or more ads

The following table describes MediaTailor behavior when the redirect response contains one or more ads.

allowMultipleAds	MediaTailor behavior
`false` (default)	MediaTailor selects one ad from the redirect response and discards the remaining ads. The selected ad inherits the sequence value from the parent Wrapper Ad. Selection strategy: MediaTailor selects the lowest sequenced ad in the redirect response. If there is no sequenced ad available, MediaTailor picks a standalone ad, if available.
`true`	When the wrapper has a sequence attribute, MediaTailor inserts redirect ads at the wrapper's position. When the wrapper has no sequence attribute, MediaTailor inserts redirect ads after the parent's sequenced ads. The resolved ads form their own buffet group.

Example allowMultipleAds=false, wrapper has sequence=2

Parent VAST:


<VAST>
  <Ad sequence="1" id="seqAd1">...</Ad>
  <Ad sequence="2">
    <Wrapper allowMultipleAds="false">
      <VASTAdTagURI>https://ads.example.com/vast</VASTAdTagURI>
    </Wrapper>
  </Ad>
  <Ad sequence="3" id="seqAd3">...</Ad>
  <Ad id="standAloneAd1">...</Ad>
  <Ad id="standAloneAd2">...</Ad>
</VAST>

Wrapper redirect response:


<VAST>
  <Ad sequence="1" id="redirectSeqAd1">...</Ad>
  <Ad sequence="2" id="redirectSeqAd2">...</Ad>
  <Ad id="redirectStandAloneAd1">...</Ad>
</VAST>

Resolved VAST:


<VAST>
  <Ad sequence="1" id="seqAd1">...</Ad>
  <Ad sequence="2" id="redirectSeqAd1">...</Ad> <!-- redirectSeqAd1 selected, inherits Wrapper's sequence (2) -->
  <Ad sequence="3" id="seqAd3">...</Ad>
  <Ad id="standAloneAd1">...</Ad>
  <Ad id="standAloneAd2">...</Ad>
</VAST>

Playback order:

seqAd1
redirectSeqAd1
seqAd3

Example allowMultipleAds=false, wrapper has no sequence

Parent VAST:


<VAST>
  <Ad sequence="1" id="seqAd1">...</Ad>
  <Ad>
    <Wrapper allowMultipleAds="false">
      <VASTAdTagURI>https://ads.example.com/vast</VASTAdTagURI>
    </Wrapper>
  </Ad>
  <Ad sequence="3" id="seqAd3">...</Ad>
  <Ad id="standAloneAd1">...</Ad>
  <Ad id="standAloneAd2">...</Ad>
</VAST>

Wrapper redirect response:


<VAST>
  <Ad sequence="1" id="redirectSeqAd1">...</Ad>
  <Ad sequence="2" id="redirectSeqAd2">...</Ad>
  <Ad id="redirectStandAloneAd1">...</Ad>
</VAST>

Resolved VAST:


<VAST>
  <Ad sequence="1" id="seqAd1">...</Ad>
  <Ad id="redirectSeqAd1">...</Ad> <!-- redirectSeqAd1 selected, inherits Wrapper's sequence (UNDEFINED) -->
  <Ad sequence="3" id="seqAd3">...</Ad>
  <Ad id="standAloneAd1">...</Ad>
  <Ad id="standAloneAd2">...</Ad>
</VAST>

Playback order:

seqAd1
seqAd3

Note

redirectSeqAd1 is not played because it has no sequence defined.

Example allowMultipleAds=true, wrapper has sequence=2

Parent VAST:


<VAST>
  <Ad sequence="1" id="seqAd1">...</Ad>
  <Ad sequence="2">
    <Wrapper allowMultipleAds="true">
      <VASTAdTagURI>https://ads.example.com/vast</VASTAdTagURI>
    </Wrapper>
  </Ad>
  <Ad sequence="3" id="seqAd3">...</Ad>
  <Ad id="standAloneAd1">...</Ad>
  <Ad id="standAloneAd2">...</Ad>
</VAST>

Wrapper redirect response:


<VAST>
  <Ad sequence="1" id="redirectSeqAd1">...</Ad>
  <Ad sequence="2" id="redirectSeqAd2">...</Ad>
  <Ad id="redirectStandAloneAd1">...</Ad>
</VAST>

Resolved VAST:


<VAST>
  <Ad sequence="1" id="seqAd1">...</Ad>
  <!-- Redirect response merged at sequence 2 -->
  <Ad sequence="1" id="redirectSeqAd1">...</Ad>
  <Ad sequence="2" id="redirectSeqAd2">...</Ad>
  <Ad id="redirectStandAloneAd1">...</Ad>
  <Ad sequence="3" id="seqAd3">...</Ad>
  <Ad id="standAloneAd1">...</Ad>
  <Ad id="standAloneAd2">...</Ad>
</VAST>

Playback order:

seqAd1
redirectSeqAd1
redirectSeqAd2
seqAd3

Example allowMultipleAds=true, wrapper has no sequence

Parent VAST:


<VAST>
  <Ad sequence="1" id="seqAd1">...</Ad>
  <Ad>
    <Wrapper allowMultipleAds="true">
      <VASTAdTagURI>https://ads.example.com/vast</VASTAdTagURI>
    </Wrapper>
  </Ad>
  <Ad sequence="3" id="seqAd3">...</Ad>
  <Ad id="standAloneAd1">...</Ad>
  <Ad id="standAloneAd2">...</Ad>
</VAST>

Wrapper redirect response:


<VAST>
  <Ad sequence="1" id="redirectSeqAd1">...</Ad>
  <Ad sequence="2" id="redirectSeqAd2">...</Ad>
  <Ad id="redirectStandAloneAd1">...</Ad>
</VAST>

Resolved VAST:


<VAST>
  <Ad sequence="1" id="seqAd1">...</Ad>
  <Ad sequence="3" id="seqAd3">...</Ad>
  <!-- Redirect response merged after sequenced ads -->
  <Ad sequence="1" id="redirectSeqAd1">...</Ad>
  <Ad sequence="2" id="redirectSeqAd2">...</Ad>
  <Ad id="redirectStandAloneAd1">...</Ad>
  <Ad id="standAloneAd1">...</Ad>
  <Ad id="standAloneAd2">...</Ad>
</VAST>

Playback order:

seqAd1
seqAd3
redirectSeqAd1
redirectSeqAd2

Metrics and log monitoring

Changes to existing metrics

When ad buffet is enabled, the following existing metrics change behavior.

Metric	Behavior with ad buffet
`AdDecisionServer.Ads`	Count of sequenced ads parsed from the ADS response.
`AdDecisionServer.Duration`	Total duration of sequenced ads only.
`AdDecisionServer.FillRate`	Fill rate calculated using sequenced ads only.

New metrics

The following new metrics are available when ad buffet is enabled.

Metric	Description
`AdNotReady.SequencedAd`	Number of sequenced ads not ready for insertion.
`AdNotReady.StandaloneAd`	Number of standalone ads not ready for insertion (excludes ads skipped with `StandaloneAdNotNeeded`).
`Avail.FillRate.SequencedAd`	Percentage of avail filled by sequenced ads.
`Avail.FillRate.StandaloneAd`	Percentage of avail filled by standalone ads.
`Avail.FilledDuration.SequencedAd`	Duration of avail filled with sequenced ads.
`Avail.FilledDuration.StandaloneAd`	Duration of avail filled with standalone ads.
`AdsBilled.SequencedAd`	Number of billed ads that are sequenced.
`AdsBilled.StandaloneAd`	Number of billed ads that are standalone.
`SkippedReason.StandaloneAdNotNeeded`	Emitted when a standalone ad was not needed because all sequenced ads were successfully inserted.

New skipped ad reason

The following new skipped ad reason is available when ad buffet is enabled.

Reason	Description
`STANDALONE_AD_NOT_NEEDED`	A standalone ad was eligible but not needed because all sequenced ads were successfully inserted. No error beacon is fired.

For standalone ads that are not eligible for insertion (for example, VPAID or transcode not ready), the actual failure reason is emitted (for example, TRANSCODE_IN_PROGRESS or VPAID_AD) as SkippedReason.

Error beaconing

MediaTailor handles error beacons for ad buffet as follows:

Sequenced ads that fail – error beacons are fired (existing behavior).
Standalone ads that are not ready (ad transcode status is not SUCCESS) – error beacons are fired (same as sequenced ads).
Unused standalone ads that were eligible for insertion but not needed – no error beacons are fired.

ADS event changes

When ad buffet is enabled, MediaTailor adds the following fields to two ADS events:

VAST_RESPONSE event

Each VastAd in the VAST_RESPONSE event includes the following fields.

Field	Type	Description
`buffetGroup`	String	MediaTailor generated string that defines which buffet group the ad belongs to.
`sequence`	Int	The sequence value from the `Ad` element.

FILLED_AVAIL event

Each entry in creativeAds and skippedAds in the FILLED_AVAIL event includes the following fields.

Field	Type	Description
`buffetGroup`	String	MediaTailor generated string that defines which buffet group the ad belongs to.
`sequence`	Int	The sequence value from the `Ad` element.

These fields allow you to determine:

Which ads were parsed as sequenced versus standalone
Which ads were inserted and their type
Why a sequenced ad was skipped and whether a standalone ad replaced it
Why a standalone ad was unavailable