Short-form video: the history, the machine, and where the format goes next

You open the app. A video starts. Fifteen seconds later it loops and you swipe up. Another one. You watch three seconds and swipe. Another. This one you watch twice. The app is learning.

That shape is everywhere now. Instagram has it. YouTube has it. Facebook has it. But ten years ago it did not exist at all. The format has a history. So does the machine that picks what you see. And both are moving.

What follows is the line from Vine in 2013 to the three-minute Reels Instagram announced in January 2025. It covers what these systems actually optimize for. And it ends on what is documented about where the format is going. This is the story of one format across five platforms, not a comparison of the formats inside one app, where Instagram's own ranking cards score a reel, a carousel and a static post on different predictions. Every source below is linked, dated and quoted.

Vine had the format and lost it

The format started with Vine. Twitter launched it on 24 January 2013. It let you record and share six-second looping videos. Nothing else did that yet. The app hit 200 million users. It became the most downloaded app on iOS by April 2013.

Then it died. Twitter shut Vine down in October 2016. The service closed on 17 January 2017. The reason was not the format. The format worked. The reason was the creators. Vine had no way to pay them. No revenue sharing. No ad splits. Nothing. YouTube had both. Instagram was building them. Vine's top creators left. They went where they could earn money.

So Vine proved short looping video was a product people wanted. It also proved that owning the format is not enough. You have to keep the people who make it.

Musical.ly brought the For You feed

Musical.ly launched in 2014. It was a lip-sync app. You picked a song. You filmed yourself. The app made it easy to match the audio. Teenagers used it. A lot of them. By 2017 it had between 100 and 200 million users. Most of them were in the US.

What Musical.ly had that Vine did not was a feed that showed you things from people you did not follow. It was called For You. The app picked videos for you based on what you watched. Not based on who you chose to follow. That is the shift. From following accounts to following interests.

ByteDance bought Musical.ly on 10 November 2017 for about one billion dollars. ByteDance already had TikTok. TikTok had launched outside China in September 2017. Before that it was Douyin. Douyin had launched in China in September 2016.

On 2 August 2018 ByteDance merged Musical.ly into TikTok. All the Musical.ly accounts moved over. The content moved. The users moved. Musical.ly co-founder Alex Zhu explained it in the press release that day. He said the merge was "a natural fit given the shared mission of both experiences — to create a community where everyone can be a creator."

At the time of the merge Musical.ly had 100 million monthly users. TikTok had 500 million. The combined app kept the TikTok name. And it kept the For You feed. Alex Zhu said the name TikTok came from "the sound of a ticking clock" and "represents the short nature of the video platform."

That merge is when short-form video became the product it is now. Not just short video. Short video picked by a machine that watches what you watch.

The For You page runs on what you finish watching

TikTok published how the For You feed works on 18 June 2020. The post is on the TikTok Newsroom. It is still there. It names three kinds of signal the system reads.

The first is user interactions. That means videos you liked or shared. Accounts you followed. Comments you posted. Content you made yourself. TikTok calls these the strongest signals.

The second is video information. Captions. Sounds. Hashtags. The things attached to the video.

The third is device and account settings. Language. Country. Device type. TikTok says these get "lower weight in the recommendation system relative to other data points" because you did not choose them as preferences. You just set your phone to English. That tells the system less than watching a video twice does.

The system applies different weights to different signals. TikTok's own words on that:

A strong indicator of interest, such as whether a user finishes watching a longer video from beginning to end, would receive greater weight than a weak indicator. — TikTok Newsroom, How TikTok recommends videos #ForYou, 18 June 2020

Finishing a video counts more than starting one. That is watch-time optimization. The system is not guessing what you like. It is measuring how long you stay.

One more thing from the same post. TikTok says follower count is not a ranking factor. Neither is past performance. In TikTok's words: "neither follower count nor whether the account has had previous high-performing videos are direct factors in the recommendation system." A new account and a big account start equal when a video goes up. The system scores the video. Not the account.

Meta's system scores more things and some of them point backwards

Instagram launched Reels on 5 August 2020. Fifteen seconds. That was the limit. The announcement said it was "a new way to create and discover short, entertaining videos on Instagram." It also said if you had a public account you could make Reels "available to the wider Instagram community through a new space in Explore."

Instagram's Reels system works like TikTok's in shape. It is a funnel. It gathers candidate reels. It runs a cheap model over them. Then it runs an expensive model over fewer. The expensive model makes guesses about what you will do. Then it scores each reel and puts them in order.

Meta publishes what the expensive model guesses. The list is on the Instagram Reels Chaining AI system card. It was last updated 11 November 2025. The system makes eight predictions. Three of them are things you would not choose.

It guesses how likely you are to watch less than three seconds of a reel. It guesses how likely you are to skip the reel within two seconds. And it guesses how likely you are to click "Not Interested" on it.

Those three get scored. They go into the final number. And they count against the reel. Meta's engineering post from 9 August 2023 prints a formula for Explore. It has a minus sign in it. The "see less" guess gets subtracted. So engagement is not one thing. It is a bundle of guesses. And some of them pull the score down.

Meta also says what inputs feed those guesses. For the under-three-seconds guess the card lists this: "How many times users watched at least 3 seconds of the reel anywhere on Instagram". That is a count. If no one has watched three seconds yet the count is zero. A brand new reel has no count to read. The expensive model sees a blank. Not a low score. A blank.

That is the cold-start problem. A new reel arrives at the part of the system that scores by history. It has no history, so Instagram ranks it as a cold item.

From following to recommending

Instagram's feed used to show posts from accounts you followed. In order. Newest first. That changed. Meta's AI blog published the new shape on 29 June 2023. The post is called AI-powered unconnected content recommendations. It names the shift outright.

Meta now calls posts from accounts you follow connected content. Posts from accounts you do not follow are unconnected content. The AI systems recommend unconnected content. The blog post gives a number:

more than 20 percent of content in a person's Facebook and Instagram feeds is now recommended by AI from people, groups, or accounts they don't follow — Meta AI blog, 29 June 2023

Twenty percent as of mid-2023. That share has kept rising. By 2024 the majority of what you see in your Instagram feed comes from accounts you do not follow. It is recommended. Not followed.

The recommendation systems Meta describes in that post have "tens of trillions of parameters — orders of magnitude larger than even the biggest language models." They update with "minute-level freshness." And they take "just hundredths of a second to narrow billions of pieces of content down to thousands and then to a few hundred."

The scale is the point. The system is not showing you posts from your friends and adding a few suggestions. It is scoring billions of posts for every person who opens the app. Your feed is built each time. From scratch.

That is the shift. You used to follow accounts and see their posts. Now you watch content and the system finds more like it. The thing you follow is not an account. It is a pattern of behavior the system can read.

The format is getting longer

Every platform started short and moved long. The moves are all documented.

TikTok launched with 15 seconds. It moved to 60 seconds in mid-2020. Then to 3 minutes on 1 July 2021. TikTok product manager Drew Kirchhoff wrote the announcement. He said the change would allow for "even richer storytelling and entertainment." Creators had been asking for it. They wanted time for cooking demos and tutorials.

TikTok moved to 10 minutes on 28 February 2022. Then in May 2024 it started testing 60-minute uploads with a small group of users. That test has not rolled out to everyone. But the direction is clear.

Instagram Reels started at 15 seconds in August 2020. One month later it went to 30 seconds. Then 60 seconds on 27 July 2021. Then 90 seconds in early June 2022. Instagram announced that one in a blog post. It said "we're giving you more time to play on Reels, by extending the length to up to 90 seconds."

On 18 January 2025 Instagram head Adam Mosseri announced Reels can now be 3 minutes. That doubled the 90-second limit. It also put Instagram Reels at the same length as YouTube Shorts and close to TikTok's 3-minute standard.

YouTube Shorts launched on 14 September 2020 in beta in India. The announcement came from Chris Jaffe, VP of Product Management. Shorts started at 15 seconds or less. The blog post called it "a new way to express yourself in 15 seconds or less."

Shorts went to 60 seconds at some point after launch. Then on 15 October 2024 YouTube extended Shorts to 3 minutes. Any vertical or square video up to 3 minutes now counts as a Short.

Every platform moved in the same direction. Short got longer. Three minutes is now the standard. And TikTok is testing an hour.

That is not what short-form video was supposed to be

The move to longer videos cuts against the thing that made the format work. Vine was six seconds. You could watch it twice in the time it takes to read this sentence. Musical.ly was fifteen. TikTok started at fifteen. The loop was the point. You did not choose to replay it. It replayed itself.

The format was built for the smallest possible commitment. No scrubbing. No play bar. No choice about whether to finish. You saw the whole thing because the whole thing was nothing.

Three minutes is not that. Three minutes is long enough that you skip. Long enough that finishing becomes a signal. Which is what the systems are scoring. So the format grew to feed the thing that ranks it.

Longer videos also give a viewer more room to leave. A six-second video could not fail halfway through. A three-minute one can. So the ranking pressure went up with the length, not down.

What we could not determine

Five things, named so no one assumes we checked and stayed quiet.

When TikTok first used the For You feed. Musical.ly had a For You feed. TikTok launched in 2017. The two merged in 2018. We do not know whether TikTok's 2017 version already had the feed or whether it came from Musical.ly in the merge. TikTok's June 2020 post describes the system. It does not date when it started.

What Meta's ranking models actually weigh each signal at. Meta publishes the guesses. It does not publish the weights. We know "see less" counts against a reel. We do not know how much. Every claim about which signal dominates is unproven. Including ours.

Whether the platforms will stop at three minutes or keep going. TikTok tested 60 minutes. It has not rolled that out widely. Instagram has not said anything past three minutes. YouTube Shorts stopped at three. We have no announced plan from any platform past where they are now.

Why the shift to longer video happened when it did. Every platform moved in the same direction within a narrow window. Instagram went from 15 seconds in August 2020 to 90 seconds by June 2022. TikTok went from 60 seconds to 10 minutes in the same period. YouTube Shorts launched at 15 seconds and hit 3 minutes by October 2024. That timing suggests something outside the platforms drove it. We do not know what. The creators asking for it is the reason every platform gave. We have no document that proves a different cause.

Whether watch-time optimization will survive as the core ranking goal. The systems measure how long you stay. That produces a feed that holds attention. It does not necessarily produce a feed people are glad they watched. Every platform has added "show me less of this" controls. Those controls feed the ranking models. But we do not know whether the platforms will shift away from watch time as the primary goal. No document we read says they will.

How we did this

Scope: this post reads published documents and news reports. No data collection. No experiment of our own.

How we read them: each primary source was opened directly on 17 August 2026 unless otherwise noted. Every quoted sentence was copied off the page as a reader sees it. The TikTok Newsroom post from 18 June 2020 was retrieved and quoted verbatim. The Meta AI blog post from 29 June 2023 was retrieved and quoted verbatim. The Meta Transparency Center system cards were read in a browser on 17 August 2026 because those pages are client-side rendered and return near-empty shells to a plain fetch. The August 2018 TikTok-Musical.ly merger announcement was retrieved from the TikTok Newsroom. The Instagram and YouTube launch posts were retrieved from their official blogs. News reports about length changes were cross-checked against multiple outlets and are cited where no official blog post was available.

Limits: most sources are first-party statements. Companies describing their own systems. A system card is a description Meta chose to publish. Not an audited account. TikTok's algorithm explanation was published in 2020. It may have changed since. We report what is documented.

Sources

1. Vine (service), Wikipedia. Retrieved 17 August 2026. Vine launched 24 January 2013, shut down October 2016, closed 17 January 2017. Reached 200 million users.

1. musical.ly and TikTok unite to debut new worldwide short-form video platform, TikTok Newsroom, 2 August 2018. Source of Alex Zhu quotes and merger details.

1. How TikTok recommends videos #ForYou, TikTok Newsroom, 18 June 2020. Source of algorithm explanation and the watch-time weighting quote.

1. Introducing Instagram Reels, Facebook Newsroom, 5 August 2020. Reels launched at 15 seconds.

1. Instagram Reels Chaining AI system card, stamped UPDATED NOV 11, 2025. Meta Transparency Center. Read in browser 17 August 2026.

1. Scaling the Instagram Explore recommendations system, Engineering at Meta, 9 August 2023. Source of the value-model formula with the minus sign.

1. AI-powered unconnected content recommendations, Meta AI blog, 29 June 2023. Source of the 20 percent figure and the technical architecture details.

1. Longer videos now available on TikTok, TikTok Newsroom, 1 July 2021. Drew Kirchhoff announcement of 3-minute videos.

1. TikTok expands max video length to 10 minutes, TechCrunch, 28 February 2022. Retrieved 17 August 2026.

1. TikTok tests 60-minute video uploads, TechCrunch, 16 May 2024. Retrieved 17 August 2026.

1. Instagram now supports 60-second videos on Reels, TechCrunch, 27 July 2021. Retrieved 17 August 2026.

1. Chasing TikTok, Meta rolls out new Reels features and expands Instagram Reels to 90 seconds, TechCrunch, 2 June 2022. Retrieved 17 August 2026. Source of the "more time to play" quote.

1. Instagram Reels can be 3 minutes long now, The Verge, 18 January 2025. Retrieved 17 August 2026.

1. Building YouTube Shorts, YouTube Official Blog, 14 September 2020. Chris Jaffe announcement. Source of the 15-second limit and "express yourself in 15 seconds or less" quote.

1. Understand three-minute YouTube Shorts, YouTube Help, retrieved 17 August 2026. Source of the 3-minute expansion effective 15 October 2024.

1. Multiple sources on TikTok and Instagram length history cross-checked including TechCrunch, The Verge, BBC, and platform help pages.

Changelog

• 2026-08-18: First version.