Modify Video Speed with ffmpeg

By  on  

I watch a lot of sports and recently I've become fascinated with some of the methodologies they use to illustrate events within the game.  I don't have their advanced TV software or hardware, of course, but I do have a love for ffmpeg, which allows me to do everything from clip videos to change video formats, create tacky highlight videos with emo techno music combine audio and video, and more.

One of my favorite TV sports illustration techniques is speeding video up (time-lapse) or slowing it way down (slo-mo replay); naturally I wanted to know how to manipulate video speed with ffmpeg.  It turns out all you need to do is pass in filter with a PTS (presentation timestamp) value:

Faster Video Speed

ffmpeg -i input.mp4 -filter:v "setpts=0.5*PTS" output.mp4

Slower Video Speed

ffmpeg -i input.mp4 -filter:v "setpts=2*PTS" output.mp4

The lower the PTS value, the faster the time-lapse video is generated.  If you use a larger value, the video will display in slower motion.

Adjust video and audio

If you care to sync the audio speed with the video speed, things get a bit more complicated:

ffmpeg -i input.mp4 -filter_complex "[0:v]setpts=0.5*PTS[v];[0:a]atempo=2.0[a]" -map "[v]" -map "[a]" output.mp4

More confusing is that the atempo setting seems to require reverse logic to setpts ; i.e. doubling speed seems to require a different multiple.

I recently used this slow-mo technique on a highlights video downloaded from YouTube to draw my own conclusions about a specific play.  The ability to manipulate video so easily, without a UI, also makes for easy automation of media, especially when you combine this technique with clipping video -- you get just the frames you want at the speed you want.  ffmpeg FTW!

Recent Features

  • By
    Creating Scrolling Parallax Effects with CSS

    Introduction For quite a long time now websites with the so called "parallax" effect have been really popular. In case you have not heard of this effect, it basically includes different layers of images that are moving in different directions or with different speed. This leads to a...

  • By
    JavaScript Promise API

    While synchronous code is easier to follow and debug, async is generally better for performance and flexibility. Why "hold up the show" when you can trigger numerous requests at once and then handle them when each is ready?  Promises are becoming a big part of the JavaScript world...

Incredible Demos

  • By
    Editable Content Using MooTools 1.2, PHP, and MySQL

    Everybody and their aerobics instructor wants to be able to edit their own website these days. And why wouldn't they? I mean, they have a $500 budget, no HTML/CSS experience, and extraordinary expectations. Enough ranting though. Having a website that allows for...

  • By
    CSS Selection Styling

    The goal of CSS is to allow styling of content and structure within a web page.  We all know that, right?  As CSS revisions arrive, we're provided more opportunity to control.  One of the little known styling option available within the browser is text selection styling.

Discussion

  1. Rob

    How can I decrease the speed of a video & audio by 7.5%?

  2. Al

    Very helpful, thanks! One tip about the relation between setpts setting and atempo setting: You don’t actually need to calculate the other one, use the following syntax (e.g. to have a 1.3x faster output):

    ffmpeg.exe -i input.mp4 -filter_complex "[0:v]setpts=PTS/1.3[v];[0:a]atempo=1.3[a]" -map "[v]" -map "[a]" output.mp4
  3. Tarun

    @AI thanks for the tip!! it really is amazing!!

  4. Kay

    Just ran ffmpeg basic command (no speed switches), e.g.

    ffmpeg -i  

    and got a video that is smaller than the original but:
    – all the video is fast and at the front of the file then
    – the rest is blank and audio only
    I don’t get it?

    Never had this issue before…

  5. Kay

    ok that should have been:

    ffmpeg -i inputfile outputfile
    

    so the basic command

Wrap your code in <pre class="{language}"></pre> tags, link to a GitHub gist, JSFiddle fiddle, or CodePen pen to embed!