What Is the Twixtor Effect?
Twixtor is an Adobe After Effects plugin that allows you to manipulate the speed of a video. Most video-editing apps have the option of slowing down a video, but it usually results in a choppy video that looks unnatural. This is due to the limited amount of frames.
Twixtor solves this issue by utilizing optical flow.
Optical flow is the process of analyzing footage and filling in the missing frames. It visually guesses what the images would look like between frames and creates new ones to fill in the gaps. This makes for a continuous string of frames, producing a stunning, smooth result.
After Effects isn’t available for iOS, so you’ll have to take a different approach to achieve the Twixtor effect on iPhone.
How to Get Smooth, Slow-Motion Videos on iPhone
Before we get into the more involved Twixtor-like effects, it’s important to be able to make smooth, slow-motion videos that aren’t choppy. It’s not as simple as slowing down a video, you need specific effects, and luckily there are two apps on iOS that provide that.
Optical Flow on SloPro
SloPro is one of the few video editing apps that offers optical flow as an effect on its own.
After importing your video, tap the red Edit icon in the top-right corner to open the editor window. If necessary, use Clip In and Clip Out to trim the video down to the part that you want to edit. Speed In and Speed Out divides it into clips.
Drag the cursor over the clip and tap the box in the top left—a number of fast and slow speed options will appear.
If you select a slow speed, tap the box in the top right and select Optical Flow. This will render the clip with optical flow, creating that smooth Twixtor effect.
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The free version of the app will leave a watermark on the video, but you can simply crop it out.
Download: SloPro (Free, in-app purchase available)
Mixtor and Motion Blur on Video Star
Video Star is a powerhouse, iOS-only editor that offers nearly every effect you can think of; but we’re only going to focus on velocity and motion blur. Before you can start, you’re going to need the VS Motion Blur and the Velocity & Time Mapper packs.
The Pro version gives you access to all of the packs. To acquire these upgrades, go to the thunderbolt icon from the home screen.
Getting that super smooth, Twixtor effect on Video Star requires some back-and-forth editing. Import your video, and from the editing window tap on New, then Velocity. It’ll open the Velocity Mapper and you’ll see a green line, which represents the video source, and a red dot, which is a keyframe that indicates the point of a change in speed.
Drag that keyframe up several values to speed up the video and tap Create—yes, we’re going to speed it up first. Then, tap on New again, select Transform, look for VS Motion Blur and select it. It will give you options to alter the intensity and type of motion blur. If this intimidates you, leave it on the default settings.
After creating the clip with motion blur, go back to Velocity Mapper, and drag the keyframe down to however slow you want the footage.
It should already be relatively smooth thanks to adding motion blur, but the latest Video Star update introduced Mixtor, a Twixtor-like effect that generates optical flow. To add it, tap the icon at the bottom left with the running avatar and select Better Mixtor.
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Since Mixtor is not quite as powerful as Twixtor, it’s better to combine it with motion blur. However, you can skip that step and slow down the video with Mixtor alone, which also means you won’t have to buy the VS Motion Blur pack.
Download: Video Star (Free, subscription available)
How to Make a Velocity Edit on an iPhone
You’ve probably seen velocity edits all over social media and wondered how people get that fast-slow-fast-slow effect. With the help of the aforementioned apps, you can easily create your own Twixtor-like velocity edits on an iPhone.
SloPro and a Second Video Editing App
You can make a velocity edit on SloPro alone since it has fast and slow speed options. However, if you intend to make an edit with audio, you’re going to need to use it in conjunction with another video editing app that allows audio import.
There are a multitude of video editing apps to achieve a velocity edit with, provided that they offer cut or split features as well as speed or time-changing features.
First, slow down the entire video in SloPro, add optical flow, and export it. Import it to your video-editing app of choice, and cut it into clips wherever you want the speed to alternate over the audio.
Locate the speed or time-changing feature, and on every second clip, turn the speed up. Now you should be left with a string of clips that oscillate between fast and slow—that is a velocity edit.
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It tends to look better when the slow-motion part falls on the beat drop, followed by the sped-up bit, and so on. Keep playing around with it until you get a feel for where to cut the clips and which speed to set them to.
Velocity Mapper on Video Star
Video Star is comprehensive enough to be the only editor you need for velocity edits, given that you’ve purchased the necessary packs.
Create a slow-motion clip by following the aforementioned steps. Now, open that clip in Velocity Mapper yet again.
At the bottom right, you’ll see an encircled plus or minus sign; this is for adding and removing keyframes. Drag the playback slider to maneuver the white dot on the grid, this is where the keyframe will be added. You can drag the keyframe around on the grid.
Every keyframe allows you to change the speed of that specific part of the clip. To get that speed-alternating effect, keep adding keyframes and place them in such a way that the green line looks like a sine wave.
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Move them around until you’re satisfied with the playback in concert with the audio (if you’re using sound), and remember to set it to Better Mixtor.
Since the clip that you’re using is already in slow-motion, you’ll want to keep the entirety of the green line above value 1 on the graph. Anything below that could result in the slow parts of the velocity edit being too slow. After creating the clip, you can trim off the still frame at the end.
Alternately, open an unedited clip in Velocity Mapper—if you haven’t already applied motion blur, remember to add it afterward. Now you can add and edit the keyframes across value 1 on the graph, following the same sine wave shape as mentioned above. And always keep it on Better Mixtor.
Making Twixtor Video Edits on iPhone
You don’t need complex editing software to get the Twixtor effect. SloPro and Video Star are a lot simpler to use than After Effects and have all the tools you need to make smooth slow-motion or velocity edits on your iPhone.
Looking to make some memories from media on your iPhone or iPad? Here are the best free video editing apps for iPhone and iPad.
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