user16589: I recorded a "slow-motion" video with my Android phone and transferred it to my Windows computer. Now I have an MP4 file with a frame-rate of 240 fps. But when I play the video, it plays at normal speed.  I want to create a video that I can upload to YouTube or Facebook that plays at 1/8 speed (30 fps).
I thought I could do that with the free Movie Maker that comes with Windows. But when I select 1/8 speed it comes out chunky. It looks like the software converted the video to 30 fps when it loaded, and is now playing back that 30 fps video at 1/8 speed.  I'm guessing that Movie Maker can't do what I want.
How do I create a video so that when someone plays that video they see it in slow-motion?

user1871: You can use ffmpeg, a free command-line tool, to do this:
ffmpeg -i input.mp4 -vf setpts=8*PTS -r 30 -crf 18 output.mp4

This slows down the video 8 times and output is 30 FPS.

16589: <p>I recorded a "slow-motion" video with my Android phone and transferred it to my Windows computer. Now I have an MP4 file with a frame-rate of 240 fps. But when I play the video, it plays at normal speed.  I want to create a video that I can upload to YouTube or Facebook that plays at 1/8 speed (30 fps).</p>

<p>I thought I could do that with the free Movie Maker that comes with Windows. But when I select 1/8 speed it comes out chunky. It looks like the software converted the video to 30 fps when it loaded, and is now playing back that 30 fps video at 1/8 speed.  I'm guessing that Movie Maker can't do what I want.</p>

<p>How do I create a video so that when someone plays that video they see it in slow-motion?</p>
 1871: <p>You can use <a href="https://ffmpeg.zeranoe.com/builds/" rel="noreferrer">ffmpeg</a>, a free command-line tool, to do this:</p>

<pre><code>ffmpeg -i input.mp4 -vf setpts=8*PTS -r 30 -crf 18 output.mp4
</code></pre>

<p>This slows down the video 8 times and output is 30 FPS.</p>
