A pre-roll is a video advertisement that plays before the content a viewer has chosen to watch. It occupies the first slot in a video stream: the player loads, an ad request goes out, a commercial of roughly six to thirty seconds runs, and only then does the selected video begin. The position exists because it is the one moment in a video session where attention is produced by the mechanics of playback rather than earned by the material around it. Nobody has decided yet that the content is dull, and nobody has left.

In industry vocabulary, pre-roll is one of three linear in-stream positions, alongside mid-roll and post-roll. Linear means the advertisement takes over the player and interrupts content rather than overlaying it. In-stream means it runs inside a player whose main purpose is playing video that the viewer came for. Both distinctions carry commercial weight, because both are encoded as fields that determine what a buyer pays.

How a pre-roll request is assembled

When playback starts, the player or an embedded software development kit issues an ad request. On the open web and in apps, that request typically flows through a publisher ad server and then into a supply-side platform, which converts it into an OpenRTB bid request containing a video object.

The field that identifies the position is startdelay. A value of 0 means pre-roll. A positive integer means a mid-roll beginning that many seconds into the content. Values of -1 and -2 signal generic mid-roll and generic post-roll where exact timing is unavailable, according to the Start Delay Modes list in AdCOM and to Microsoft's Xandr documentation. The field has carried that meaning since OpenRTB 2.0, published in January 2012.

Sitting beside it is plcmt, which separates genuine in-stream inventory from everything else. IAB Tech Lab clarified the four values on February 4, 2025: instream (1), accompanying content (2), interstitial (3) and no content or standalone (4). To qualify as instream, a placement must meet several conditions at once, including sound on by default and demonstrated user intent to watch video. A pre-roll that runs in a muted player next to an article is not, under that taxonomy, an in-stream pre-roll.

The rest of the video object narrows the auction: minduration and maxduration in seconds, mimes for accepted file types, protocols for the VAST versions the player understands, linearity, playbackmethod, and the skip triplet of skip, skipmin and skipafter.

What comes back

The winning bid returns a VAST document. VAST, the Video Ad Serving Template, is an XML specification maintained by IAB Tech Lab that tells a player which file to fetch, how long it runs and what to report. IAB Spain's first supply-side platform guide, covered by PPC Land in April 2026, separates three things practitioners routinely conflate: the VAST standard, the VAST tag that is called, and the VAST document that comes back.

Inside a linear pre-roll response, Duration sets runtime, MediaFiles carries the renditions, and the skipoffset attribute states when a skip control appears. TrackingEvents holds the measurement pixels that make video reporting granular: start, first quartile, midpoint, third quartile and complete. UniversalAdId identifies the creative for frequency capping and competitive separation. AdVerifications passes the signals used by the Open Measurement SDK, which measures viewability and playback state on the device, as IAB Europe's programmatic connected television guide documents.

Where several breaks are scheduled in one content item, VMAP handles placement. A pre-roll is expressed as an ad break with timeOffset="start" and breakType="linear", per the IAB specification.

Server-side ad insertion complicates the picture. In streaming, the pre-roll is stitched into the manifest rather than played by a client-side plugin. Google's Ad Manager documentation for dynamic ad insertion in live streams shows how fragile the timing is: the pre-roll start point is derived by subtracting 2.5 target-duration intervals from the session creation timestamp, and the pre-roll is dropped entirely if it overlaps a mid-roll unless the dai-pre=1 parameter is set.

Who operates the slot

On the sell side, the position is configured in a video ad server. Google Ad Manager exposes pre-roll, mid-roll and post-roll as targetable positions, and where breaks contain several advertisements, buyers can also target position within the pod. Magnite's SpringServe, Publica and comparable systems perform the same function for streaming publishers.

On the buy side, the slot is bought through demand-side platforms, through reservation deals, or through platform-native interfaces. Google's own documentation prices its skippable in-stream format on cost per view, charging when a viewer reaches thirty seconds or completes a shorter advertisement, with the skip control appearing after five seconds.

In connected television the standalone pre-roll has largely become the opening slot of a pod. Magnite applied machine learning to pod construction on October 24, 2025, on the argument that issuing multiple bid requests per break to guarantee fill inflates costs across the chain.

Origins and evolution

Pre-roll predates the infrastructure that now describes it. Short video advertisements appeared on the open web in the early 2000s, before standard scheduling or measurement existed, and YouTube began carrying advertising formats in 2007.

Standardisation arrived in 2008, when the IAB published VAST 1.0 alongside VPAID, the interface definition for interactive video. VAST 2.0 added quartile tracking. VAST 3.0, released in 2012, introduced skippable advertisements through skipoffset and improved error reporting. VMAP arrived the same year, with a 1.0.1 revision in 2014.

The economics changed on December 1, 2010, when YouTube launched TrueView, letting viewers skip after five seconds and charging advertisers only for views that were not skipped. The format reached mobile in August 2012.

Measurement caught up next. The Media Rating Council issued display viewability guidelines in March 2014 and video guidelines in August 2015, setting the threshold at 50% of pixels in view for two continuous seconds.

VAST 4.0 followed in 2016 with mezzanine files and server-side stitching support, VAST 4.1 in November 2018, VAST 4.2 in June 2019, and VAST 4.3 in December 2022. SIMID, which moved interactive playback control from the creative to the player, entered public comment in 2019 as the replacement for VPAID. IAB Tech Lab then published the VAST CTV Addendum in July 2024 to retrofit registered ad identifiers and SIMID support into VAST 2 and VAST 3 implementations still in service.

Why the format matters to marketers

Scale is the first reason. United States digital video advertising revenue grew 25.4% to $78 billion in 2025, and IAB projects the category will exceed $80 billion in 2026, having doubled in five years. Within that total, social video reached $31.9 billion against connected television's $29.3 billion.

The second reason is that pre-roll is where format rules translate into budget. YouTube alone runs six distinct video formats with different length limits, skip behaviour and billing models, a complexity PPC Land examined in its account of what programmatic buyers get wrong. Duration conventions vary by property: pre-roll on IMDb runs six to 15 seconds, according to Amazon Ads, while IAB Tech Lab's connected television format guidelines of December 11, 2025 set 1920 by 1080 as the standard creative size.

Limitations and disputes

The format's central weakness is that a guaranteed impression is not guaranteed attention. Research by Teads with the MediaMento Institute, published in September 2025 and reported by PPC Land, measured a 48% attention rate for smart television home screen placements, 16 percentage points above YouTube skippable pre-roll.

Completion rate, the metric most often cited in defence of streaming pre-roll, faces a sharper objection. PPC Land documented the argument that a 98% completion rate is automatic rather than earned on non-skippable inventory, and that optimising toward it pushes algorithms to the cheapest supply that logs a view. DoubleVerify found that 34 of every 100 monitored connected television impressions did not appear in streaming content at all, surfacing instead on music, fitness and screensaver applications, while fraud schemes rose 140% in the first quarter of 2026 against the same period a year earlier.

Classification is contested as well. The Trade Desk blocked Yahoo's open marketplace video inventory for some advertisers on June 17, 2024, citing IAB definitions of in-stream. Google tightened its video publisher policies effective April 1, 2024, restricting how many placements may autoplay in view and barring audio advertisements from muted placements. Adform implemented OpenRTB 2.6 outstream signals in April 2025 for the same reason.

Pre-roll and its neighbours

Mid-roll and post-roll occupy the same linear in-stream family but different points in the timeline. In podcasting the ordering of value inverts: listeners reaching the midpoint have demonstrated commitment, making mid-roll more valuable than pre-roll, as PPC Land's analysis of podcast ad load records.

Bumper describes a short non-skippable unit, conventionally six seconds. It frequently runs in the pre-roll position but is defined by duration and skippability, not placement.

Outstream video plays inside articles and feeds rather than in a content player. It may appear before nothing at all, which is precisely why the plcmt taxonomy separates it as accompanying content or standalone.

Non-skippable in-stream is a billing and control distinction, not a position. A pre-roll may be skippable or not.

Two unrelated senses persist. In cinema, pre-roll denotes the pre-show block, which PPC Land has described as ten to fifteen minutes of seated dwell time. In production, pre-roll is the run-up recorded before a take.

Recent developments

The classification layer is being rebuilt. IAB released the Redefining Media Types Standard for public comment on July 9, 2026, with the window closing August 8, 2026. It sorts video by viewer orientation rather than distribution technology, and applies eight binary impression-level attributes, among them whether an impression is skip-enabled or completion-required. IAB Tech Lab intends to encode the framework into OpenRTB and AdCOM.

Platform activity continues to widen where pre-roll appears. LinkedIn launched BrandLink in May 2025, placing three to thirty second pre-roll advertisements ahead of publisher and creator video in the feed. Amazon added programmatic guaranteed deals for Prime Video in August 2024 with an option to serve only on pre-roll. X operates Amplify Pre-rollacross 22 countries for verified video publishers.

At the same time, publishers are buying inventory that sits outside the position entirely. Hearst News selected Magnite in April 2026 for formats that activate outside pre-roll and mid-roll, and IAB Tech Lab's December 2025 format work standardised pause, menu, overlay and screensaver units. The oldest slot in digital video is no longer the only one being sold.

Timeline

  • Early 2000s: Short video advertisements appear on the open web, inserted without common scheduling or measurement standards.
  • 2007: YouTube begins carrying advertising formats.
  • 2008: IAB publishes VAST 1.0 and VPAID, establishing a common protocol for video ad serving and interactivity.
  • December 1, 2010: YouTube launches TrueView, allowing viewers to skip after five seconds and billing only unskipped views.
  • January 2012: OpenRTB 2.0 defines the startdelay field, encoding pre-roll as the value 0.
  • 2012: VAST 3.0 adds skippable advertisements via skipoffset; VMAP 1.0 defines ad break scheduling.
  • August 2012: YouTube extends skippable in-stream advertisements to mobile.
  • 2014: VMAP 1.0.1 published; MRC issues display viewability guidelines in March.
  • August 2015: MRC sets video viewability at 50% of pixels in view for two continuous seconds.
  • 2016: VAST 4.0 introduces mezzanine files and server-side stitching support.
  • November 2018: VAST 4.1 released, adding Open Measurement verification support.
  • June 2019: VAST 4.2 released with SIMID support, following SIMID's public comment period.
  • December 2022: VAST 4.3 released.
  • March 2023: IAB Tech Lab publishes video ad format guidelines redefining in-stream.
  • April 1, 2024: Google's streamlined video publisher policies take effect.
  • June 17, 2024: The Trade Desk blocks Yahoo open marketplace video inventory for some advertisers.
  • July 2024: IAB Tech Lab publishes the VAST CTV Addendum 2024.
  • February 4, 2025: IAB Tech Lab clarifies the plcmt placement values.
  • October 24, 2025: Magnite applies machine learning to ad pod construction in SpringServe.
  • December 11, 2025: IAB Tech Lab releases connected television ad format standards for public comment.
  • July 9, 2026: IAB releases the Redefining Media Types Standard, with comment closing August 8, 2026.

Summary

Who: Publishers and their video ad servers create the slot; supply-side platforms expose it programmatically; demand-side platforms and platform-native buying interfaces purchase it. IAB and IAB Tech Lab define the specifications that describe it, including VAST, VMAP, OpenRTB and AdCOM.

What: A pre-roll is a linear in-stream video advertisement that plays before the content a viewer selected, identified in bid requests by a startdelay value of 0 and scheduled in VMAP through an ad break with timeOffset="start".

When: The format appeared on the open web in the early 2000s and was standardised from 2008 with VAST 1.0. Skippable pre-roll arrived on YouTube on December 1, 2010. Classification work continues, with IAB's Redefining Media Types Standard in public comment until August 8, 2026.

Where: Pre-roll runs on video platforms, publisher sites and applications, connected television and streaming services, and in social feeds carrying in-stream video. Server-side ad insertion stitches it into streaming manifests rather than playing it client-side.

Why: The position guarantees an impression before a viewer can disengage, which made it the first reliably saleable unit in digital video. That guarantee is also its limitation: an impression logged before content begins says little about attention, and both attention research and fraud measurement indicate the gap between delivery and effect is wider than completion metrics suggest.