The short answer
There is no single right length for a video teaser. The placement sets it. An autoplaying preview on your own site or app should run five seconds or less, or come with a pause control. A promo that viewers cannot skip before a YouTube video is limited to 6 seconds as a bumper ad, or 15 seconds as a non-skippable in-stream ad (20 seconds in some markets). A skippable promo can run longer, but its first 5 seconds have to work on their own, because that is when the Skip button appears. A vertical teaser on YouTube Shorts can run up to 3 minutes, but should stay under one minute if it contains footage or music someone else could claim. For TikTok in-feed ads, TikTok's own creative tips recommend 21 to 34 seconds out of the 5 to 60 it allows. The practical rule: cut the shortest version first, then extend it for placements that allow more, rather than trimming a long promo down.
What a teaser is for
A teaser is a short cut of a longer video, such as an episode, a match, an interview or a documentary, whose only job is to get the right people to watch the full thing. That makes it different from a summary, which explains the content, and from a highlight, which is meant to be watched on its own. The difference matters for length. A teaser that is too short does not show enough for a viewer to decide. A teaser that is too long starts to replace the content: the viewer has already seen the best moment and has no reason to open the full video. It also decides what to measure. The result of a teaser is viewing of the full asset, not views or completion of the teaser itself.
On your own site and app: five seconds, or a pause button
Teasers on a publisher's own pages usually play as moving previews in a grid, a feed or on hover. Here accessibility rules set the boundary. WCAG 2.2 success criterion 2.2.2 (Pause, Stop, Hide) requires a way to pause, stop or hide moving content that starts automatically, lasts more than five seconds and is shown alongside other content. The W3C's explanation counts content that starts from an indirect interaction, such as hovering over or focusing an element or scrolling it into view, as starting automatically. So a hover or in-feed preview should either loop a clip of five seconds or less or carry a visible pause control. The preview should also play muted and keep a static poster as a fallback. A teaser that the visitor deliberately clicks to play is a different case and can run as long as the story needs. Our guide to video preview best practices covers the autoplay, motion and loading rules in detail.
YouTube in-stream: 6 seconds, 15 seconds and the five-second skip
Google Ads Help sets hard limits for promos that run before, during or after other YouTube videos. Bumper ads can be a maximum of 6 seconds, cannot be skipped and are offered in select markets for awareness and reach. Non-skippable in-stream ads can be a maximum of 15 seconds, or 20 seconds in EMEA, India, Malaysia, Mexico and Singapore. Skippable in-stream ads have no fixed maximum, but viewers can skip them after 5 seconds: a countdown runs for the first 5 seconds and is then replaced by a Skip button. Google counts a view of a skippable ad when someone watches 30 seconds, or the whole ad if it is shorter, and says the ad must be at least 12 seconds long for views to be counted. For a program teaser this means three distinct cuts rather than one: a 6-second version that names the program and shows one moment, a 15-second version that adds the setup, and a skippable version whose first 5 seconds carry the hook and the title. Google's ABCD guidance for YouTube creative points the same way: drop viewers in from the start, and introduce the brand or product from the start and keep it present. For a teaser, the brand is the show, the event or the publisher.
Shorts, Reels and TikTok: the limits are long, the useful length is shorter
Vertical feeds allow far more time than most teasers need. YouTube Help says videos with a square or vertical aspect ratio of up to three minutes are categorized as Shorts. The same article sets a rule that matters for broadcasters: a Short longer than one minute with an active Content ID claim of any type, including a manual claim, is blocked globally, so it cannot be played or recommended and is not eligible for monetization. Shorts under one minute are not subject to that limit. A teaser that contains licensed music, league footage or syndicated material should therefore stay under 60 seconds unless every second is cleared. Meta's ads guide for Instagram Reels allows video from 0 seconds to 15 minutes in a 9:16 ratio, recommends sound and captions, and suggests keeping at least 14% of the top, 35% of the bottom and 6% of each side clear of text and logos. TikTok's 7 Top Tips document says in-feed video ads can run 5 to 60 seconds and recommends 21 to 34 seconds, based on TikTok's own creative research from May to July 2021; the checklist in the same document asks advertisers to be mindful of a recommended length of 9 to 15 seconds. When a platform's own guidance varies like this, treat it as a starting range to test, not a rule.
How to cut one teaser into every length
Start with the moment that best represents the full video without giving away its ending: the question before the answer, the build-up before the goal, the reveal before the explanation. Build the shortest version first, five or six seconds with one moment, the program or event name visible and nothing that depends on dialogue, since many placements start muted. Extend it to 15 seconds by adding the setup that makes the moment understandable. Extend it to between 20 and 60 seconds for social feeds by adding a second beat and a clear pointer to where the full video is. Then recompose each version for the destination's shape: 9:16 for Shorts, Reels and TikTok, square where that is accepted, 16:9 for in-stream. Keep captions and graphics inside each platform's safe zones. Finally, keep every version tied to the source asset ID and the destination URL, so the teaser always leads to the right full video and can be withdrawn with it.
Test length instead of guessing
Platform guidance gives ranges, not answers for your audience. Compare two or three lengths in the same placement, for the same audience and over the same period, and judge them on what happens next: how many people start the full video and how long they watch it. Do not judge teasers on their own completion rate. A shorter teaser will almost always be completed more often, which says nothing about whether it sent anyone to the full video. For skippable in-stream promos, also compare how many viewers stay past the 5-second skip point. Keep the winning length for each placement, write it into the teaser rules, and test again when a platform changes its limits, as YouTube did when Shorts grew to three minutes.
Where automation fits, and a checklist
Cutting several lengths and shapes for every title is the part that does not scale by hand. Minute-ly.com Video Previews creates short previews from new uploads or an existing VOD library: duration, editorial exclusions and delivery requirements are defined once, previews are generated without a separate manual edit for each title, and each one stays linked to its original video. Smart Composition recomposes 16:9 video to vertical and square shapes by considering the scene rather than holding a fixed center crop. The rules still come from your team. Before publishing a teaser, check: the moment represents the full video and does not give away the ending; on your own site, automatic motion stops within five seconds or has a pause control; non-skippable cuts fit 6 or 15 seconds; skippable cuts carry the hook and title in the first 5 seconds; Shorts with any third-party footage or music stay under one minute; captions and graphics sit inside each platform's safe zones; each version links to the right full video; and length is judged by viewing of the full asset, not by teaser completion.