SIMID (Secure Interactive Media Interface Definition) is an IAB Tech Lab standard that defines a secure communication protocol between video/audio players and interactive ad creatives. It replaces VPAID for interactive ad use cases, using a sandboxed iframe and the postMessage API instead of a shared JavaScript context.

How does SIMID work with VAST?

A SIMID creative is referenced from a VAST 4.x document via the element inside . The element must have type="text/html" and apiFramework="SIMID". The player loads the creative URL into a sandboxed cross-origin iframe and communicates with it via the SIMID postMessage protocol.

What is the difference between SIMID and VPAID?

VPAID runs ad creative in the same JavaScript context as the player (insecure, blocks SSAI). SIMID runs the creative in a sandboxed cross-origin iframe. The player controls media loading and playback; the creative communicates via postMessage. SIMID enables SSAI, pre-caching, and fault isolation. A fatal creative error cannot crash the player.

Yes. The IAB Tech Lab has officially deprecated VPAID. SIMID replaces the interactivity use case, and OMID (Open Measurement SDK) replaces the verification use case. vastlint flags VPAID usage as a warning in VAST tags.

SIMID: Secure Interactive Media Interface Definition

SIMID (Secure Interactive Media Interface Definition) is the IAB Tech Lab standard for rich interactive ad experiences in streaming video and audio. It defines how a publisher's media player and an interactive ad creative communicate, replacing the older and now-deprecated VPAID standard.

The current version is SIMID 1.2, released December 2022.

Why SIMID exists

VPAID gave ad creatives full access to the player's DOM and JavaScript context: powerful, but deeply insecure and incompatible with server-side ad insertion (SSAI). A single buggy or malicious VPAID script could crash the player or the entire publisher page.

SIMID draws a hard security boundary. The interactive creative runs in a sandboxed cross-origin iframe. The player manages all media loading and playback. The creative and the player communicate only through the postMessage API using a well-defined protocol. A fatal error in the creative cannot affect the player or the publisher's page.

How SIMID fits into the VAST ecosystem

VAST describes the ad metadata (media files, tracking URLs, companion ads). SIMID describes how the player and an interactive creative layer talk to each other during ad playback. A SIMID creative is referenced from a VAST 4.x document as one of the assets inside <MediaFiles>.

The `<InteractiveCreativeFile>` element

To serve a SIMID creative, add an <InteractiveCreativeFile> element inside <MediaFiles>. Two attributes are required:

type="text/html": the MIME type of the creative resource
apiFramework="SIMID": tells the player which API to use

A third optional attribute, variableDuration="true", signals that the ad can extend the ad break duration (e.g. for a game or survey). If the player does not support variable duration, it must not render the ad at all.

<MediaFiles>
  <MediaFile delivery="progressive" type="video/mp4" width="1280" height="720">
    <![CDATA[https://example.com/ad.mp4]]>
  </MediaFile>

  <!-- SIMID interactive layer -->
  <InteractiveCreativeFile type="text/html" apiFramework="SIMID" variableDuration="true">
    <![CDATA[https://adserver.com/ads/creative.html]]>
  </InteractiveCreativeFile>
</MediaFiles>

Players that do not support SIMID will play the video file and ignore the <InteractiveCreativeFile>. This makes SIMID gracefully degradable.

How the player loads a SIMID creative

Player creates a hidden, cross-origin iframe.
Sets iframe.src to the URL from <InteractiveCreativeFile>.
Listens for the creative's createSession postMessage; responds with resolve.
Sends SIMID:Player:init with environment parameters (viewport size, version, skip settings, etc.). Waits for resolve.
Starts media playback; sends SIMID:Player:startCreative.
Makes the iframe visible, positioned over the media element.

From this point, both sides exchange messages: the player sends media events (SIMID:Media:timeupdate, SIMID:Media:pause, etc.) and the creative requesting actions (SIMID:Creative:clickThru, SIMID:Creative:requestFullscreen, etc.).

SIMID vs. VPAID: comparison

Feature	VPAID	SIMID
Security model	Shared DOM and JS context with player (insecure)	Sandboxed cross-origin iframe, no DOM or JS access to player
Media control	Creative manages ad video loading and playback	Player manages all media loading and playback
SSAI support	Not possible	Fully supported
Pre-caching	Only the VPAID script; video cannot be pre-cached	Both video and SIMID creative can be pre-cached
Fatal error impact	Can crash the player or publisher page	Isolated to the creative iframe only
Communication	Direct JS function calls in shared context	postMessage API across security sandboxes
Creative MIME type	`application/javascript`	`text/html`
Audio advertising	Out of scope	Supported
CTV / native players	Requires HTML video element	Works in native or web player with sandboxed web view
Status	Deprecated by IAB Tech Lab	Current standard (v1.2)

SIMID message categories

All SIMID messages are JSON objects exchanged via postMessage. They fall into three groups:

Media events: sent by the player when the media element fires events (e.g. SIMID:Media:timeupdate, SIMID:Media:ended)
Player messages: player lifecycle events sent to the creative (e.g. SIMID:Player:init, SIMID:Player:adSkipped, SIMID:Player:resize)
Creative messages: requests from the creative to the player (e.g. SIMID:Creative:clickThru, SIMID:Creative:requestFullscreen, SIMID:Creative:reportTracking)

Every message expects either a resolve or reject response, making the protocol fully acknowledged and debuggable.

VAST versions that support SIMID

The <InteractiveCreativeFile> element was introduced in VAST 4.0 and is present in 4.1, 4.2, and 4.3. SIMID creatives are not expressible in VAST 2.0 or 3.0.

Does vastlint validate SIMID?

vastlint validates VAST XML structure, which includes checking that <InteractiveCreativeFile> is correctly placed inside <MediaFiles> and that apiFramework is present. It does not validate the SIMID creative's JavaScript/HTML content or the runtime postMessage protocol (which requires a live player environment). See the rules reference for all VAST structural rules.

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