How to Create Slow Motion in DaVinci Resolve With Optical Flow

In this tutorial we’ll be looking at how to create slow motion in DaVinci Resolve with Optical Flow. We’ll be using techniques that will allow is to create slow motion effects even if your captured footage is at a lower frame rate. 

What You’ll Need

To follow this tutorial, you’ll need your own version of DaVinci Resolve. For this tutorial we’ll be working with DaVinci Resolve Studio 17 and the tools we’ll be using are only available in the paid studio version. However there is still a lot of great tools in the free version of DaVinci Resolve, so I definitely suggest you check it out.

We’ll also be using some stock footage from Envato Elements.  Below, you’ll find a link to the assets we’ll use for this tutorial:

• Group of Young Diverse Friends Walking at Night
• Legs of Skater Doing Kickflip Trick Outdoors
• Woman Unplugging Electric Car at Charging Station

Today we’re looking at DaVinci Resolve and we’re looking at a setting called Retime and Scaling.

But more specifically within that setting, we’re looking at two things: optical flow and speed warp. We’ll get into how these can work together to get a buttery, smooth, slow motion effect. 

Although these are powerful tools, it doesn’t always work perfectly. Depending on the type of footage used you can get varying results and will work best with  a piece of footage that has the least amount of motion and complexity in it already.

So I’ll take you through three different examples of three different pieces of footage, and will show you a varying level of results. 

For our first piece of footage we have this group of friends just walking through this tunnel here having a chat with their coffees.

The first thing you want to do is highlight the clip, and then hit Control – R or Right Click > Retime Controls.

It will then give you this little drop down where it says 100% and if you click the arrow next to it, you’ll get a few more options.

Now we want to define a part in the clip where we want it to slow down. Once you’ve done that go ahead and hit the little black arrow next to 100% and select Add Speed Point.

Then we’ll go through the clip and find where we want it to speed up again. Then simply add another speed point.

Now this hasn’t actually done anything to the clip so far. However you can see we’ve now split the clip into three sections and we want to slow down the middle section. 

The 100% means that the section is playing back at 100% of its speed. To change the speed click on the arrow and go to Change Speed. This will allow you to choose from some percentage options to either slow down the clip or speed it up. We’re going to slow it down and select 25%.

Once that’s been done, you’ll see that it has extended the clip which is indicated via the yellow arrows at the top and the percentage number at the bottom.

However this will result in a jittery, stretched clip which is not usable. So how can we start getting something that’s usable and not jittery? First we need to highlight the clip again and go up to the Inspector and then go to Retime and Scaling.

Click into it and change the following settings:

• Retime Process: Optical Flow
• Motion Estimation: Speed Warp

Now upon playing the clip back you won’t actually notice any difference. Well, because we’re doing so much under the hood here and it’s so process intensive, we won’t be able to see the results straight away. 

For us to see the results we will need to render it in place. To do this Right Click the clip and select Render in Place.

Once that’s done, you’ll notice that we no longer have any of the speed points that were added. So hit Control – R on the keyboard or Right Click > Retime Controls to see what’s going on and you’ll see that our clip is no longer split into three and it is now at 100% speed again. 

What this means is that the clip has now been rendered with all the changes that we made previously which is why it is important to make all the changes you want before rendering in place.

Now if you play the clip back you should find that the slow motion part of the clip is pretty smooth and usable. There may be certain parts where the more exaggerated movements (such as the hand moving on the left) may still look a bit weird. However as a whole, this process has worked really well!

Now let’s move on to the second clip. Here we have a lady charging up her electric car. Again we’ve split the clip into three sections. However this time, we have sped up the first and third sections by 400%. This will make the clip feel more interesting and dynamic.

Now let’s Right Click on the clip and choose Retime Curve. This will display the graph view of the clip.

Click on the little arrow button on the top left to drop down some more options and make sure Retime Speed is clicked. Remove Retime Frame as we’re not focusing on it right now.

Click on the retime speed line and it will give you this little key frame that you can select and adjust where your in and out points are, which is useful.

However what we want to do here is create a curve to make our speed transitions smoother. To do this, select the keyframe and then click on the curve keyframe button at the top. This will curve out the speed line, and give the keyframe handles so that you can adjust the speed.

Let’s change the speed of the middle section of the clip to 10% and then go to the inspector and change the following settings just as we did with the previous clip:

• Retime Process: Optical Flow
• Motion Estimation: Speed Warp

Render the clip by right clicking the clip and selecting Render in Place and wait for it to finish to see the results! 

Now if you play the rendered video back you’ll see the slow motion section of the clip will appear as if it has been shot at 300 frames per second or more, despite being originally 25 frames per second.

This process works great when the clip doesn’t contain quick and exaggerated or complex movements. In our final clip we have used the same techniques as described above, however the results are far from perfect and has resulted in a warped mess. Which is why it is important to choose the clips wisely when using this technique.

So that’s how you can create slow motion in DaVinci Resolve with Optical Flow. Now that you have a good understanding on how to make this effect, why not experiment with your own footage! I hope you found this tutorial helpful and that you’ve learned some new tips and tricks that you can use for your own projects. See you next time!

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