SSAI stands for server-side ad insertion: the splicing of advertising into a video stream on a server, upstream of the viewer, so the device receives one continuous sequence of programme and commercial rather than two things it has to join. The alternative, client-side ad insertion, leaves the player to interrupt the content, call an ad server, fetch a creative and play it back. SSAI removes that call from the device.

The technique exists because television-like playback over the internet proved hard to deliver. Streaming applications run on hundreds of hardware profiles, many of which cannot execute JavaScript and some of which cannot host a measurement software development kit. A client-side break on a congested connection produces a black frame or a resolution drop at the exact moment a broadcaster has sold. Moving the join upstream fixes that, and as a consequence makes the advertisement indistinguishable from the programme to an ad blocker.

How a stream gets stitched

Adaptive streaming splits video into short segments and describes them in a text file: a playlist in HTTP Live Streaming, a manifest in DASH. SSAI works by rewriting that file rather than the video.

Break positions have to be marked first. Live and broadcast-derived streams carry SCTE-35 cue messages, the in-band signalling standard published by the Society of Cable Telecommunications Engineers in 2001 as Digital Program Insertion Cueing Message for Cable and last revised as ANSI/SCTE 35 2023r1 on November 30, 2023. A cue-out declares the timestamp and planned duration of a break; a cue-in marks the return. On-demand assets more often use VMAP, the IAB format listing break offsets.

Delivery is then rerouted. The content delivery network treats the insertion service as the manifest origin, so every viewer request passes through it. AWS Elemental MediaTailor documents the sequence in five steps: detect the marker, call the ad decision server with break duration and viewer parameters, process the VAST or VMAP response, personalise the manifest, fire tracking beacons. Because each session gets its own manifest, a million concurrent viewers generate a million distinct playlists.

Timing is the binding constraint. In live streams the cue arrives seconds before the splice point, and everything else happens inside that window. Google Ad Manager's documentation shows how narrow the margins are: the live pre-roll start point is calculated by subtracting 2.5 target-duration intervals from the session creation timestamp, and the pre-roll is dropped if it overlaps a mid-roll unless the dai-pre parameter is set to 1. MediaTailor follows up to seven levels of VAST wrapper redirect before giving up. Google moved that unwrapping into the ad server itself in December 2024, reporting an 83% reduction in error rates in partner testing.

Conditioning the creative

An advertisement produced for a website will not drop cleanly into a broadcast-grade ladder. The stitcher transcodes each creative to match the stream's resolution, bitrate rungs and codec profile, which is why source quality matters more here than in client-side delivery. VAST 4.0 introduced the mezzanine file in 2016 for that reason: a mastering-quality source transcodes well, a pre-compressed rendition does not.

IAB Tech Lab put numbers on the requirement when it released six standardised connected television ad formats on December 11, 2025. Ready-to-serve files are specified across four tiers from 360p to 1080p and above, with target bitrates from 500 to 700 kbps at the low end to 2,000 to 3,500 kbps at ultra HD, though connected television vendors may ask for 10,000 to 30,000 kbps. Recommended mezzanine bitrates reach 50 Mbps variable or 15 to 30 Mbps constant.

Where the impression goes

The measurement problem follows from the architecture. When the server calls the ad decision server and fires the beacons, those requests originate from a data centre address with a server user agent, and to a measurement vendor they resemble fraud rather than a household.

The standards response has been to make the proxy declare itself. VAST 4.0, published in January 2016, recommended that stitching services pass X-Forwarded-For and X-Device-User-Agent. VAST 4.1, in November 2018, hardened this into a list of headers an ad-stitching proxy must send, including X-Device-IP, X-Device-User-Agent, X-Device-Referer and X-Device-Accept-Language. Ad servers expose matching macros: Google Ad Manager's dynamic ad insertion set includes IFA, IFA type, limit ad tracking, user IP address, SCTE-35 signals and a session stream identifier.

The Media Rating Council addressed the gap in guidance published in August 2021, developed with roughly 50 participating organisations. It holds that client-initiated counting remains the requirement, and that server-to-server tracking may be unable to satisfy it while being vulnerable to invalid traffic filtration, because it arrives from one address. Proposed remedies include disclosure of provider IP ranges, a certification scheme, and authentication through mutual TLS or ads.cert. The document also sets a hard rule: providers claiming to use SSAI must be verified as such, and their traffic must be discretely measurable for invalid traffic or treated as unknown rather than valid.

Origin and evolution

Server-side insertion predates the connected television market it serves. Yospace, a British vendor acquired by RTL Group on January 9, 2019, dates its first deployment to 2011 and ran what it describes as the first live proof of concept for over-the-top dynamic ad insertion with ITV in 2012, followed by launches with Network Ten in Australia in 2014 and DirecTV in 2016.

Standardisation arrived alongside commercial deployment. VAST 4.0 added mezzanine files and server-side stitching support in 2016. Amazon made the capability a cloud primitive when AWS Elemental MediaTailor reached general availability on November 26, 2017. IAB Tech Lab published guidelines for the identifier for advertising on OTT platforms on April 3, 2018, addressing the absence of cookies on television hardware and advising publishers to ensure the identifier and limit-ad-tracking settings survive the stitch. The IAB and MRC video impression guidelines were updated in June 2018 with SSAI guidance, superseded in part by the August 2021 document.

Why it matters for buyers and sellers

Server-side insertion is the default plumbing of the largest growth category in video. Streaming television advertising spending reached $33.35 billion in 2025, most of it transacted programmatically, although estimates differ: IAB Tech Lab cited 75% of connected television spend when it opened its format standardisation initiative in October 2024, while Google put roughly 86% of the inventory in the programmatic channel two months later.

Audio followed the same path under a different name. Dynamic insertion accounted for more than 90% of United States podcast advertising revenue by the 2023 IAB study, roughly double its share three years earlier, and Apple extended the model to video episodes with its February 2026 HTTP Live Streaming release.

Limitations and disputes

The same opacity that protects the stream from ad blockers protects fraud from detection. Oracle disclosed StreamScam in November 2021, an operation that spoofed 28.8 million valid United States household IP addresses by exploiting SSAI to report impressions for video never delivered. HUMAN Security disrupted a comparable scheme, NewsJunkie, in July 2026, in which one seller spoofed device, application and IP details through server-side insertion at close to two billion bid requests daily. DoubleVerify recorded a 140% rise in connected television fraud schemes in the first quarter of 2026.

Delivery to an unwatched screen is a separate problem. DoubleVerify's Todd Randak said in December 2025 that more than a third of connected television impressions reach television-off environments, contributing to an estimated $1 billion in annual waste. IAB research found 43% of connected television buyers doubt where their advertising actually ran.

Capability is the third constraint. Open Measurement and SIMID interactivity execute in the player, so a purely server-side path carries those components without running them. IAB Europe's April 2026 connected television guide accepted the trade-off and attached a disclosure duty, requiring publishers and vendors to state when SSAI is in use and whether impressions are counted server-side, client-side or through a hybrid method.

Adjacent terms

Client-side ad insertion, or CSAI, streams content and advertising separately and lets the player append them just before viewing. Measurement is richest here, because pixels and verification tags fire from the player. Blocking is also easiest.

Server-guided ad insertion, or SGAI, splits the difference: the server controls break signalling while the client fetches and renders the creative, restoring player-side measurement but requiring modern interstitial support.

Dynamic ad insertion, or DAI, describes the outcome rather than the mechanism: the advertisement is decided at request time instead of being fixed in the file, and can be implemented either side.

Ad stitching and manifest manipulation are used interchangeably with SSAI, though the first describes joining the media and the second the technique used to do it.

Recent developments

The direction of travel is towards hybrids rather than replacement. IAB Australia published Server-Guided Ad Insertion - An Explainer on August 6, 2026, written by technology lead Jonas Jaanimagi, which compares the three models across eleven dimensions and argues that server-guided insertion still depends on player support much of the installed television base lacks. Its recommended path is per-session fallback: server-side insertion for legacy reach, server-guided for premium, live and interactive inventory. Google offers a server-guided mode through DAI Pod Serving alongside a dynamic insertion line it has continued to extend.

Verification is being pushed down to the hardware. Device attestation shipped in version 1.6 of the Open Measurement SDK in late 2025, using an adaptation of the IETF Privacy Pass protocol to establish that a bid request came from genuine television hardware, initially on Apple and Fire TV. Amazon began serving VAST 4 on third-party publisher inventory across 34 markets on September 2, 2026, while its own Stores and Fire TV surfaces still accept only VAST 2 and VAST 3 creatives.

Timeline

  • 2001: SCTE publishes the first version of SCTE-35, the in-band cue message standard later used to mark breaks in HLS and DASH
  • 2011: Yospace deploys server-side ad insertion commercially
  • 2012: First live proof of concept for over-the-top dynamic ad insertion, run with ITV in the United Kingdom
  • 2014: Live server-side insertion launches with Network Ten in Australia
  • January 2016: VAST 4.0 introduces the mezzanine file and the first guidance for ad-stitching services
  • November 26, 2017: AWS Elemental MediaTailor reaches general availability
  • April 3, 2018: IAB Tech Lab releases guidelines for the identifier for advertising on OTT platforms for public comment
  • June 2018: IAB and MRC digital video impression measurement guidelines updated with SSAI guidance
  • November 2018: VAST 4.1 makes device headers mandatory for ad-stitching proxies and adds Open Measurement support
  • January 9, 2019: RTL Group acquires Yospace
  • May 2021: Apple introduces HLS Interstitials, scheduling breaks through EXT-X-DATERANGE tags
  • August 2021: MRC publishes Server-Side Ad Insertion and OTT Guidance
  • November 2021: Oracle discloses StreamScam, spoofing 28.8 million household IP addresses through SSAI
  • December 11, 2024: Google Ad Manager introduces server-side unwrapping for connected television
  • Late 2025: Device attestation ships in Open Measurement SDK 1.6 on Apple and Fire TV devices
  • December 11, 2025: IAB Tech Lab releases six connected television ad format standards for public comment
  • April 2026: IAB Europe publishes its Guide to Programmatic for CTV, attaching disclosure duties to SSAI
  • July 2026: HUMAN Security disrupts NewsJunkie, a spoofing scheme routed through server-side insertion
  • August 6, 2026: IAB Australia publishes its server-guided ad insertion explainer
  • September 2, 2026: Amazon DSP begins serving VAST 4 on third-party publisher inventory in 34 markets

Summary

Who. Publishers, broadcasters and streaming services buy SSAI from insertion vendors including Yospace, AWS Elemental MediaTailor, Google Ad Manager, FreeWheel and Broadpeak. Ad servers and supply-side platforms make the decision; measurement vendors including DoubleVerify, Integral Ad Science and HUMAN Security attempt to verify it. IAB Tech Lab and the Media Rating Council write the rules.

What. SSAI is the insertion of advertising into a video stream on a server before delivery, usually by rewriting an HLS or DASH manifest so advertisement segments sit inside the content timeline. The device receives one continuous stream and makes no separate call for the commercial.

When. Commercial deployment dates to 2011, with standards support arriving through VAST 4.0 in 2016, VAST 4.1 in 2018, and dedicated MRC guidance in August 2021. Server-guided variants emerged from 2025 onwards.

Where. It is standard across connected television, free ad-supported streaming channels and broadcaster on-demand services, and the equivalent model dominates podcast advertising, where the same request-time substitution is called dynamic ad insertion.

Why. It delivers broadcast-quality breaks on hardware that cannot reliably run client-side advertising, and it cannot be blocked. The cost is that the impression is no longer reported by the device, which weakens verification, complicates invalid traffic filtering and has been exploited repeatedly at scale.