Tutorial: Creating slow motion (slo-mo)

I saw a Facebook post the other day that had the author showing he was utterly confused by slow motion (slo-mo).

Basically, they said they had set the camera in “slo-mo” mode, but when they played the back, it was “normal”.

I had a bit of a trawl through various groups, and it seems for newbies, slo-mo is indeed a bit of a mystery.

So, this if for those who are trying to get some slow-motion footage but failing for whatever reason. I suspect those who have been doing video for some time will know all this stuff.

Frame Rate

As you will know, video footage is made up of individual frames that are displayed quickly one after the other to give the illusion of motion. The rate at which they are played is called, not surprisingly, the frame rate, usually abbreviated to fps for frames per second.

Now there happens to be three “basic” frame rates in common usage; 24fps, 25fps and 30fps. (Purists will tell you 30fps is actually 29.97fps but I’ll stick to 30 for ease of understanding).

24fps is traditionally used in movies as it gives the so-called “cinematic” effect. 25fps is used in the PAL TV transmission system which we use here in Australia, the UK and other countries. 30fps is used by the NTSC TV system employed in the US and others.

It would seem obvious then that you could simply slow down the frame rate on playback, yes?  If you have footage at 30fps, if you play it back at 15fps it will be ½ the speed seems logical. And so it is.

But.

It also means there is not enough data there so it will appear jerky and very unnatural.

The secret is to record at a higher frame rate and THEN slow it back down.

For example, if you shoot at 50fps and then playback at 25fps, you’ll achieve the half speed, but have nice smooth video to boot.

Most cameras these days (and smartphones) will let you record at higher frame rates. Some will restrict the frame size – you might be able to record 120fps at 1080p but only 50fps at 4K resolution for example – but as long as your project stays at the appropriate frame size, that should not matter.

So to summarize with a 25 / 50 fps combo:

  1. Set your video editing project to a frame size that your fps can handle (initially stick with 1080p until you get the hang of everything).
  2. Make sure your project frame rate is 25fps
  3. Set your camera frame capture rate to say, 50fps (try and stay in multiples of the project frame rate if you can)
  4. Import the footage at the higher rate but play it back at the lower.
  5. Render out the footage

Done.

Do some experimentation with subjects such as dropping an ice cube into a glass, a dog running toward you, or a car going past focussing on the wheel turning, and play around with frame rates etc.


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