A clear explanation of SCTE-35: the broadcast standard for marking ad breaks in a video stream, how it enables ad insertion in FAST and live streaming, and why it matters.
What Is SCTE-35? Ad Insertion Markers Explained for Streaming
By Sampath Mallidi, CEO of Revidd · Last updated June 2026
SCTE-35 comes up constantly in FAST and live streaming, usually without explanation. Here is what it actually is and why it matters for monetizing a stream.
SCTE-35 is the broadcast industry standard for marking ad breaks and other cue points inside a video stream. It places signals in the stream that tell ad systems exactly when to insert an advertisement, which is what makes automated ad insertion possible in FAST channels and live streaming. SCTE-35 is maintained by the Society of Cable Telecommunications Engineers.
What Does SCTE-35 Actually Do?
SCTE-35 marks the precise points in a video stream where an ad break begins and ends, so an ad insertion system can fill that break with advertising. Without these markers, a streaming system has no reliable way to know where it is safe to place an ad.
Think of it as cue points embedded in the broadcast. When the stream reaches an SCTE-35 marker, the ad system is signaled to switch from program content to an ad, then back again when the break ends. This is the same cueing concept traditional TV has used for decades, adapted for internet streaming.
How Does SCTE-35 Enable Ad Insertion?
SCTE-35 markers work together with an ad insertion method, most commonly server-side ad insertion (SSAI), to deliver ads. The marker says when; the ad system decides what ad to serve and stitches it into the stream.
The typical flow:
The playout or encoding system inserts SCTE-35 markers at each ad break.
An ad system reads the markers and requests ads from an ad server.
The ads are inserted into the stream at the marked points, then the program resumes.
For FAST channels, this is the mechanism that turns a free channel into a revenue stream. See how it fits into a channel in our guide to launching a FAST channel, and how the ad model itself pays out in our explainer on how AVOD works.
How Do SCTE-35 Markers Travel Inside a Stream?
SCTE-35 markers ride inside the same stream as the video, so the timing stays exact. In MPEG-2 transport streams the markers sit in-band, referenced by the program map table. In HLS and MPEG-DASH, the markers are exposed as manifest-level tags that the player and ad system read.
The two most common cue messages are splice_insert, which signals the start and end of an ad break, and time_signal, which carries a timed event using segmentation descriptors. For ad-supported streaming, the practical point is this: the marker carries a precise timestamp and a break duration, so the ad system knows exactly when the break opens and how long it has to fill. This is why standards-based markers beat ad-hoc playlist tricks for live and linear content.
SCTE-35 vs SSAI vs CSAI
SCTE-35 is the marker. SSAI and CSAI are two methods of acting on that marker. The table below shows where each fits.
Term | What it is | Role in ad insertion |
|---|---|---|
SCTE-35 | In-stream cue standard | Marks where and when ad breaks start and end |
SSAI (server-side ad insertion) | Ads stitched into the stream on the server | Reads SCTE-35, inserts ads before the stream reaches the device; harder to block, smoother playback |
CSAI (client-side ad insertion) | Ads requested by the player on the device | Reads the marker client-side; easier to set up, easier for ad blockers to skip |
For FAST and live, most broadcast-grade platforms use SCTE-35 markers with SSAI, because server-side stitching holds up across the full device range, Roku, Apple TV, Fire TV, Samsung, LG, Vizio, and mobile.
Why Does SCTE-35 Matter for Broadcasters?
SCTE-35 matters because without it you cannot reliably monetize a FAST channel or live stream with ads. Any platform that claims FAST or ad-supported live capability should support SCTE-35 natively; if it does not, ad insertion will be unreliable or impossible.
It also signals broadcast-grade capability. A platform with proper SCTE-35 support, alongside an EPG and failover, is real linear infrastructure, not just a video player looping a playlist. Revidd supports SCTE-35 ad insertion in its FAST playout, with configurable ad break duration and automatic ad break insertion. Sports operators like B4Media UK run worldwide live OTT on Revidd with ad insertion, DAI, and pay-per-view layered on the same channels. For a fuller picture of the standard's history and message types, the SCTE-35 entry on Wikipedia is a reasonable starting reference.
Add SCTE-35 Ad Insertion to Your Channel
If you want a FAST or live channel that monetizes properly with standards-based ad insertion, book a demo and we will show how SCTE-35 ad breaks work in Revidd's playout.
FAQ
What is SCTE-35 in simple terms?
SCTE-35 is a standard set of signals placed inside a video stream to mark where ad breaks go. It tells an ad system exactly when to insert and end an advertisement, enabling automated ad insertion in streaming.
What is SCTE-35 used for?
It is used to cue ad breaks (and other events) in FAST channels and live streams, so an ad insertion system can place ads at the right moments. It is the foundation of monetizing ad-supported streaming.
What is the difference between SCTE-35 and SSAI?
SCTE-35 is the marker that says when an ad break occurs. SSAI (server-side ad insertion) is the method that actually serves and stitches the ad into the stream at that marker. They work together.
Do I need SCTE-35 for a FAST channel?
Yes, if you want to insert ads reliably. SCTE-35 markers are how a FAST channel signals ad breaks to ad systems. A platform without SCTE-35 support cannot do standards-based ad insertion.
Who maintains the SCTE-35 standard?
SCTE-35 is maintained by the Society of Cable Telecommunications Engineers (SCTE), the body that sets many of the technical standards used across cable and streaming.
Does SCTE-35 work with HLS and MPEG-DASH?
Yes. SCTE-35 markers are carried in-band in MPEG-2 transport streams and exposed as manifest-level tags in HLS and MPEG-DASH, so players and ad systems on Roku, Apple TV, Samsung, LG, Vizio, and mobile can act on the same cue points.
