In an ideal scenario, all your slow motion shots would be pre-planned, and you could shoot at proper frame rates to get great looking, frame accurate, slow motion. But what if you want to slow down regular old 24 or 30p footage, or you want to slow down 60 or 120p footage beyond the frames you have? Using the right post production tools with the right footage can give you stunning results.
Shooting Techniques for Perfect Slow Motion (Plus Members Only)
Rotoscope With Rotobrush (Adobe TV)
Using Shutter Speed to Control Motion Blur (Plus Members Only)
In an ideal scenario, all your slow motion shots would be pre-planned, and you could shoot at proper frame rates to get great looking, frame accurate, slow motion. But what if you want to slow down regular old 24 or 30p footage, or you want to slow down 60 or 120p footage beyond the frames you have? Using the right tools with the right footage can give you results like this…
In this segment, we talk about faking slow motion in post production, including what type of footage works best, and the results you can get using using clip speed, frame blending, timewarp, and twixtor.
With the right combination of footage and properly applied effects you can achieve stunning results
Getting glass smooth slow motion was once a pretty tough task for the average videographer. But many of today’s cameras that shoot 60 and 120p are reasonably priced, so getting that film quality slow-mo is well within our grasp, and if you’re a plus member, you can watch a full tutorial on shooting techniques for slow motion by clicking on the link.
Of course, as video producers, we’re always trying to push the technological limits, and once 40 or even 20 percent slow motion was within our reach, we immediately wanted to slow our footage down even further, or maybe we just wanted to take footage shot at standard frame rates and get regular slow motion to look better. Let’s talk about our options.
Most video editing software will allow you to slow down a video clip, but all post production slow motion abilities are not created equally. Any type of “digital” slow motion will require interpolation of frames.
Let’s say you’ve got 24p footage, and you want to play it back at 50 percent. Now those same 24 frames you captured have to cover 48 frames in real time. To achieve this, frames will either have to be repeated, causing a stuttery slow motion effect, or the software will have to create brand new frames from the preceding and following frames to fill in the blanks. Let’s take a look at some examples.
Here’s a clip of our skateboarder moving on a path at regular speed. This footage was shot at 24 frames per second. Let’s dive into premiere, to see what we can do to slow it down.
We’ve got the clip on our timeline, and by right clicking it we can select speed/duration. Now we can change the speed to 50 percent. If go to the beginning of our clip and advance one frame at a time, you’ll notice that in order to slow the clip down, Premiere is simply repeating each frame twice. This is going to result in a stuttery type of slow motion. Let’s take a look.
For a smoother look, right click the clip and select frame blend. Now if we go frame by frame, you can see that premiere is creating new frames by blending them together. Let’s take a look at the playback.
While this looks slightly better, it still appears fairly jerky.
If you don’t have additional software or plugins, you’re pretty much stuck with these options. But if you have After Effects or a third party plugin like Twixtor, you can get better results. For video tutorials on using Twixtor, you can click on the links. Now Let’s dive into after effects and see what it can do.
Using time effects in After Effects requires just a bit of prep before you start applying effects. Because after effects won’t let an effect extend the length of your clip, you can either right click the clip and enable time remapping, or you can precompose the clip by right clicking and selecting precompose, or hitting control shift c. I find it easier to precompose the clip, because it allows you to trim the clip in the precomp to avoid navigating through the original clip once your effect is applied. We’ve got our clip all trimmed, so let’s apply timewarp. Timewarp defaults to 50 percent playback. If we go frame by frame, you can see that timewarp is actually creating brand new frames with no blending. Let’s take a look at the playback.
Slowed down to 50%, the shot appears smooth. Of course, there are many settings you can change in the timewarp effect if your initial results don’t look right. For a list of controls and what they do you can click on the link.
Our first shot is a pretty good candidate for faking slow motion. If you’re going to shoot with the idea of slowing down footage in post, or you’re looking for ways to identify footage that might work without too much trouble, look for wide shots that have a static camera, plain background, and small movements from frame to frame, with minimal or no motion blur.
This in not to say that slow motion effects won’t work on other footage, but your results are going to mixed. let’s take a look at some examples.
This kickflip footage was originally shot at 120 frames per second, so we were able to slow it down to 20 percent with complete frame accuracy. But now we want to take it further and slow it down to 10 percent. Notice how the shot is fairly wide and static. Let’s see how it looks with speed adjustment, frame blending, and timewarp.
Clearly, timewarp delivers some pretty astonishing results. Even the flipping board looks good without any warping or distortion.
Now let’s up the ante. Shots that have fast motion can be difficult because the objects on screen move a great distance from one frame to the other. Couple that with a rotating skateboard and it makes it particularly tough. Let’s take a look at an example.
This kickflip over the camera in real time doesn’t show much… now here’s the shot slowed to 20 percent with actual frames because it was shot at 120 frames per second.
Next we tried applying timewarp to slow it down to 10 percent. Let’s take a look.
You can see that while the motion of the subject was pretty decent, the graphic on the board is a dead giveaway. Despite tweaking nearly every parameter in the list, we couldn’t achieve what we considered usable results.
Rather than throw in the towel we decided to give twixtor a shot. Twixtor is a 3rd party plugin designed to do exactly what we’re attempting to do, create frames when they simply don’t exist. There’s a standard version and a pro version. We applied the standard version, and here’s our result.
Clearly, on this challenging footage, twixtor was up to the task. It did help that the shot was static, and the background didn’t have a ton of detail in it.
Okay, now let’s push it to the extreme, and try to get the look of a true high speed camera. We’ll start with a shot that’s tough to slow down in the first place.
Here’s our shot in real time. It was shot at 60 frames per second. This shot is tough because there’s fast motion, a moving camera, plus those vertical bars on the fence will be problematic.
We’re going to take an isolated section and try to slow it down to a 1 percent playback speed. This is essentially mimicking a camera that shoots 2400 frames per second. Let’s see the results from our different attempts
Using timewarp, you can see that the bars of the fence don’t move in a natural way, and there’s a lot of pixels surrounding the subject that are moving with it. Not an ideal result.
The standard version of twixtor fared about the same. Again notice the fence posts and the warping occurring around the subject.
Both timewarp and twixtor pro have the ability to use a matte layer you create to aid in the creation of frames. Of course in order to do this, it means rotoscoping or masking the sections you want to slow down, which can be a time consuming process.
In our case we used the rotoscope tool to create our alpha channel matte. for more on using the rotobrush in cs6 and earlier, you can click on the link. Now let’s dive into after effects to see how we used it.
Okay, now that you have an idea on what it takes to try to work with difficult footage, let’s see if the results are worth the trouble.
Here’s the result using the matte in conjunction with timewarp. It’s a clear improvement, and well worth the rotoscoping. There are still a few frames that aren’t perfect, but the end result is much better.
Here’s the result using twixtor pro with the matte, and it’s a vast improvement as well, eliminating nearly all of the issues in a challenging piece of footage.
While some of the shots we’ve used so far were shot with faster frame rates, none of them were shot with the specific idea of using ultra slow motion effects in post. So we decided to try all the effects on a shot that was specifically taken with super slow motion in mind.
Here’s our shot at normal speed. We used a 1/2100th of a second shutter speed at 60p to get the maximum amount of frames from our 5D Mark III with no motion blur. Shooting this way requires a ton of light, which is why we headed outdoors.
If you want to know more about using shutter speed to control motion blur and you’re a plus member, you can click on the link for a full tutorial.
Ok, now let’s see how our effects handled the shot
Using timewarp yielded some good results, but we still had the issue of warping close to the subject. The standard version of twixtor looks fairly similar, again with the warping issues around our main subject
With the easy way blocked, we veered off the path to the hard road, and took the time to rotoscope the shot to see how much improvement we could get.
Using the matte for timewarp was a huge improvement, but, there were certain frames that were total dealbreakers. No matter how we tweaked it, we couldn’t get it to look right even with the matte
Finally, we applied twixtor pro and used the matte. Simply put, the twixtor pro results look perfect, and while 99 percent of the frames were completely fabricated, it had us convinced.
Converting regular footage to slow motion, or even fast frame rate footage to super slow motion is a daunting task. Many times the footage itself is going to be the determining factor in what tool you need, if it’s even possible to get the effect you want. But when it works, it offers some truly impressive results, that are well worth the time and effort. Thanks for watching.