Server-guided ad insertion, abbreviated to SGAI, is a way of placing advertising into streamed video in which the server decides where a break falls and the viewer's player fetches and plays the advertisements. The stream carries a marker for the break, but no commercial is stitched into it. When playback reaches the marker, the player requests a pod of advertisements, plays it as a separate asset and returns to the programme.

The model exists to break a long-standing trade-off. Client-side insertion gives the player direct measurement but stalls and is easy to block. Server-side ad insertion (SSAI) delivers television-like playback, yet it requires a personalised manifest, the playlist file telling a player which video segments to fetch, for every viewer. That becomes expensive when millions join a live match at once. SGAI keeps one manifest for everyone and confines personalisation to the break.

How a server-guided break works

Most deployments are built on HLS Interstitials, an extension of Apple's HTTP Live Streaming (HLS) protocol. A packager, the system that cuts encoded video into segments, writes a date-range tag into the media playlist at each break. Live break positions usually originate in SCTE-35 cue messages, a splice signal from the Society of Cable Telecommunications Engineers, as the mid-roll explainer describes. The tag carries the class com.apple.hls.interstitial, a start date, a duration and exactly one asset reference. X-ASSET-URI points to one advertisement; X-ASSET-LIST points to a JSON file listing several, each with an address and duration, which is how a pod is described. Because the tag is identical for every viewer, the playlist can be cached at the edge of a content delivery network (CDN).

X-RESUME-OFFSET tells the player where to rejoin: zero for an insertion that pauses on-demand content, or omitted for live replacement, in which case the player skips forward by the time the advertisements ran. X-RESTRICT with the values SKIP and JUMP stops viewers skipping the advertisements or seeking past them, and CUE="ONCE" keeps a rewatched section from triggering the pod again. For live streams, a later playlist update can add X-PLAYOUT-LIMIT to cut a pod short, according to Bitmovin's player documentation. Apple added an HLS_start_offset query parameter in 2022, so a viewer joining mid-break is served only the remainder.

The advertising call sits behind the asset list address. An SGAI endpoint receives the request, queries an ad decision server using VAST, the Video Ad Serving Template maintained by IAB Tech Lab, the Interactive Advertising Bureau's standards body, and converts the response into the list. The Streaming Video Technology Alliance (SVTA) publishes an Ad Creative Signaling specification whose second edition, according to the SVTA, is designed to map VAST into manifest signalling so clients can drop VAST handling.

MPEG-DASH, the Moving Picture Experts Group's adaptive streaming standard, reaches the same result through Alternative MPD events, named after its media presentation description manifest. According to castLabs, these come in two types: insert, which pauses on-demand content for a pod, and replace, which swaps a live break for a personalised one. A maxDuration attribute lets the main feed reclaim playback if play restarts early, and prefetch windows let clients load the alternative manifest at randomised moments before the break.

In Google Ad Manager, a client registers a stream session, polls for ad metadata, retrieves a pod manifest as a break approaches, and computes verification pings from timed metadata inside the ad stream. Google recommends calling its Early Ad Break Notification application programming interface (API) roughly a minute or more before each break. AWS Elemental MediaTailor, the ad insertion service of Amazon Web Services, exposes the choice per session: with the insertion mode set to PLAYER_SELECT, a player appends aws.insertionMode=GUIDED to its playlist request and receives interstitials instead of a stitched stream.

Where it sits and who runs it

SGAI changes only the last step of the transaction. The ad decision server still calls supply-side platforms (SSPs), which still run OpenRTB real-time bidding auctions for demand-side platforms (DSPs), and pod fields added in OpenRTB 2.6 in 2022, such as podid, slotinpod and poddur, describe the break to bidders. What moves is the timing of that call and the device that renders the result.

Broadcasters and streaming services run the sell side. Vendors named by IAB Australia as illustrative examples include Google Ad Manager through its dynamic ad insertion (DAI) line, alongside AWS Elemental MediaTailor, Ad Insertion Platform, Yospace, castLabs, Bitmovin and Dolby OptiView. Buyers do not configure the model, yet it decides which verification tags can execute and how impressions are counted.

Origin and evolution

The mechanism predates the name. Apple presented HLS Interstitials in 2021, and the AVFoundation classes that schedule them shipped with iOS 15 and tvOS 15.

castLabs traces warnings that per-viewer manifests were becoming a concurrency burden to Zachary Cava in 2019. On February 28, 2023, Amit Rajput, a principal product manager at Disney Streaming, described SGAI as the delivery method behind the ad-supported Disney+ Basic tier and wrote that Disney was among the first to adopt it at that scale.

AWS added HLS Interstitials for on-demand streams in MediaTailor on April 12, 2024, and SGAI was a prominent talking point at the IBC broadcasting show that September, according to IBC365. Google introduced its version for livestreams on April 7, 2025, citing squeezebacks and L-banners, in which advertising runs beside continuing content. MediaTailor extended interstitials to live streams on November 24, 2025.

DASH took longer. Alternative MPD events began as a limited tool for pre-recorded content and grew through 2024 and 2025 into near-parity with HLS, according to a paper by Thasso Griebel of castLabs, Alex Giladi of Netflix and Nicolas Levy of Qualabs. On August 19, 2026, castLabs reported that the sixth edition of ISO/IEC 23009-1 carrying them had been published.

Why the model matters to buyers

Measurement is the first argument. Server-side stitching removed the player-side beacon that verification companies relied on, as the SSAI explainer sets out, and SGAI can restore it where the Open Measurement software development kit (OM SDK) or an equivalent integration exists. Formats are the second. IAB Tech Lab released six connected television (CTV) format standards for public comment on December 11, 2025, covering pause ads, overlays and squeezebacks, and finalised their bid request signals in July 2026. IAB Australia credits SGAI with supporting L-bars, squeezebacks, side-by-side layouts and overlays.

Live sport is the third. Disney's live advertising certification, announced on January 7, 2025, required buying platforms to absorb sudden viewership surges and pre-ingest creative. Magnite's playbook for the 2026 tournament addressed bid timeouts, audience spikes and failure handling.

Limitations and disputes

Device reach comes first. SGAI works only on players that understand interstitial or alternative-manifest signalling, and IAB Australia's August 2026 explainer warned that some legacy television hardware may never qualify, recommending SSAI fallback for reach. Penthera noted in September 2024 that the HLS and DASH routes are protocol-specific, so a publisher distributing in both must maintain two monetisation paths.

Load is the second constraint. Just-in-time resolution concentrates ad calls into the narrow window where latency budgetsare tightest. Google launched DAI Prefetch for live events in March 2022 to spread such spikes, and A+E Global Media cut inbound ad server requests by 84% with pod-level auctions. Standardised prefetching, however, remains undelivered within IAB Tech Lab's Live Event Ad Playbook, as the glass-to-glass explainer records. Blocking is reduced rather than eliminated: asset lists served from recognisable ad domains can still be filtered.

Counting is the most contested point, because signalling standards define where a break goes, not how an impression is counted. IAB Europe's April 2026 CTV guide called for disclosure of whether impressions are measured server-side, client-side or through a hybrid, and the playbook's Concurrent Streams API reports SGAI streams inside SSAI totals. AWS, for its part, describes SGAI both as a complement to SSAI and as an extension of it. The IAB Australia explainer, written by Jonas Jaanimagi, calls it "an emerging implementation pattern rather than a settled category."

Claims of primacy conflict too. Ad Insertion Platform described RTBF's June 2026 launch as the first publicly documented SGAI deployment at a major broadcaster on a commercially available platform, a qualifier that coexists with Disney's in-house system three years earlier.

Not the same as

Server-side ad insertion stitches advertisements into a per-session manifest before delivery, so the player sees one stream. Client-side ad insertion leaves timing, ad requests and rendering to the application, with no server-signalled break. Dynamic ad insertion describes an outcome, an advertisement chosen at request time, and spans all three architectures. HLS Interstitials is a mechanism rather than the model: it also carries trailers and promotions, while SGAI can run on DASH or on client-scheduled breaks without it. Google's April 2025 announcement adds a further overlap, describing client-side and server-side ad stitching as two variants of SGAI.

Recent developments

IBC opens in Amsterdam today, and several pre-show announcements concern the model. On September 10, 2026, AWS extended MediaTailor to Low-Latency HLS, using interstitials so every viewer receives the same cacheable playlist and the ad decision call leaves the manifest request path. Claudio Rodrigues da Silva, head of IT at Streamco, said DSPORTS coverage of the World Cup "held six seconds glass-to-glass with ads running across every match."

Two days earlier, Bitmovin and Ad Insertion Platform said all channels of RTBF, the Belgian public broadcaster, now run on an SGAI workflow built on HLS Interstitials, following a deployment on its Auvio service that began with Belgium against Egypt on June 15, 2026 and covers live and time-shifted viewing. Moment-triggered deals, described in the play-by-play explainer, depend on breaks firing exactly where the cue says.

Timeline

  • 2019: Zachary Cava flags manifest size as a concurrency problem for large streaming services, according to castLabs
  • 2021: Apple introduces HLS Interstitials; the AVFoundation scheduling classes ship with iOS 15 and tvOS 15
  • March 2022: Google launches DAI Prefetch for live events
  • June 2022: Apple adds the HLS_start_offset parameter for viewers joining mid-break
  • February 28, 2023: Disney Streaming describes its large-scale SGAI deployment behind Disney+ Basic
  • April 12, 2024: AWS Elemental MediaTailor supports HLS Interstitials for on-demand streams
  • September 2024: SGAI becomes a prominent advertising technology talking point at IBC
  • January 7, 2025: Disney announces its live advertising certification programme
  • April 7, 2025: Google introduces server-guided ad insertion for livestreams in Ad Manager
  • August 2025: IAB Tech Lab releases the Live Event Ad Playbook
  • November 24, 2025: MediaTailor extends HLS Interstitials to live streams
  • December 11, 2025: IAB Tech Lab releases six CTV ad format standards for public comment
  • March 24, 2026: A+E Global Media case study reports an 84% cut in ad server requests through pod-level auctions
  • June 15, 2026: RTBF, RMB and Ad Insertion Platform run SGAI on Auvio during Belgium against Egypt
  • July 2026: IAB Tech Lab finalises CTV ad format signalling
  • August 6, 2026: IAB Australia publishes Server-Guided Ad Insertion - An Explainer
  • August 19, 2026: castLabs reports publication of the MPEG-DASH sixth edition with Alternative MPD events
  • September 8, 2026: Bitmovin and Ad Insertion Platform confirm all RTBF channels run on SGAI
  • September 10, 2026: AWS extends MediaTailor ad insertion to Low-Latency HLS through interstitials

Summary

Who. Broadcasters and streaming services run SGAI, using packagers, ad decision services and players from Google Ad Manager, AWS Elemental MediaTailor, Ad Insertion Platform, Bitmovin, castLabs and others. Apple, MPEG, the DASH Industry Forum and the SVTA maintain the signalling standards. Buyers reach the inventory through SSPs and DSPs, and verification companies measure it where player integrations allow.

What. An ad insertion architecture in which the server writes break markers into a manifest shared by all viewers, and the player resolves, fetches and plays a personalised ad pod at each marker before returning to content. HLS Interstitials and DASH Alternative MPD events are the two standard mechanisms.

When. The HLS mechanism arrived in 2021. Disney Streaming described deployment at scale in February 2023, vendor products spread through 2024 and 2025, the DASH standard caught up in 2026, and a broadcaster ran it on a commercial platform during the World Cup on June 15, 2026.

Where. Between the packager and the player in connected television, broadcaster video on demand, mobile and web streaming, most visibly in live sport and time-shifted viewing.

Why. It avoids generating a separate manifest for every viewer, shortens start times, restores player-side measurement and enables formats that share the screen with content. Those gains depend on modern players, prefetching at the break and commercial agreement on how an impression is counted.