You probably landed here because you saw my video pasted below on Tiktok and you’re wondering “how does that work?”. That’s what I’d like to address in this text. Here I will first give a general explanation on how a slowmotion video production mixed with realtime elements (or vice versa) is possible at all. After that I will tell about the technical approach. For this I might not go into too much detail here, because a basic knowledge of editing software is necessary. But don’t worry; for those who want to know it in detail, I will provide a step by step guide with software instructions.
kubrick 2001 by coincidence
How does slowmotion video production and realtime go together?
First a short explanation; most of you might know it already but “Slowmotion” means that a video plays slower and Realtime means that it plays in a normal speed. We’ll come back to the different speeds of slowmotion later.
Now most are wondering “how can a video be slowmotion and realtime at the same time?”. That’s exactly the trickery in this video that makes it look somewhat magical. And that is technically not as complicated as you might think. Either two seperate videos are recorded or one video is split into two layers. These two versions are then stitched together so that one part is in slow motion and the other is in normal speed. The most important thing is that the two layers still fit together logically. This means in this example that when a stick is thrown up, it should not suddenly change color or size in the air, for example, so that there is continuity.
Okay but how exactly does this work?
Here comes a detailed explanation. A step by step explanation of slow motion video production with realtime elements using this example video:
1 – It starts with a pure slowmotion video production. So you actually just need to record everything in slow motion, because a video recorded in slow motion can also be played back normally. It doesn’t work as well the other way around. Slowmotion video production, in fact, means that more frames are captured in one second than normal. A normal video has 24 or 30 frames per second. You will see this for example in the video settings of your smartphone. There it says something like 30 fps. This fps means “frames per second”. If you take a closer look, the settings for slow motion video production will say 120 fps or even 240 fps on some phones. The higher this number is, the slower the video can be played without losing quality. So go for the highest possible.
2 – When shooting, you’ll need to figure out and think through exactly how you’re going to separate it later. For example, in this video it was important to have enough sky in the frame, because I wanted the sticks to change speed from the moment they left my hand. To do that, they then had to have enough time and space to continue flying in the air while I was performing the other actions. At the same time, I also had to make sure that I no longer crossed the path of the stick. You’ll learn why this is important in the next step.
3 – Okay, after many tries you’ve shot the best version. Now it’s time for post-processing on the computer. For this I used the software After Effects. Unfortunately this software from Adobe is not free, but there are also free ones, for example Davinci Resolve. In the software the video is separated into two layers. We duplicate the video and stack them one upon the other in the timeline. One layer we set to run in slow motion. This is the layer with the sticks. The bottom layer we set as real time. Here comes the most complicated and tedious part. Each stick has to be surrounded with a path in the program from the moment it leaves your hand and tracked frame by frame. Sometimes you can automate parts of this with the Rotoscope function, but most of the time you have to do it by hand frame by frame. What we’re doing here, in fact, is cutting out the sticks so that they can continue flying on their own in slow motion, while the rest of the video continues in the background (the bottom layer) in real time.
4 – Now we need to fine-tune the transitions. Since after the moment a stick leaves my hand, another videolayer is continuing the movement, the change must not be too noticeable. In many places there will be residue and artifacts that make it noticeable that a second videolayer is running in the background. These must all be carefully “erased” frame by frame so that the illusion is not interrupted. The transition of speed from the moment the stick leaves your hand must also not be too noticeable or jerky. For this you can set a smooth transition for the speedcurve.
Conclusion and more info
As I said, this was an attempt to make the logic and procedure somewhat understandable. For people who have never had anything to do with video software or slow motion video production, this may still sound confusing. For the rest of you who already know a bit, it is maybe too superficial. If there are many who comment and want to know more, I will create a detailed step by step guide in the next few days. If you want to receive the detailed version, sign up for the newsletter below with your email address. And if you want to know what else I’m doing besides Tiktok tutorials 🙂 check out the Take9 video production home page. Have fun experimenting with slowmotion video production !