You've probably been there. You're at a wedding, or maybe watching your dog do something remarkably stupid in the backyard, and you realize too late that you should’ve recorded it in slo-mo. It’s frustrating. Most people think if they didn't toggle that specific setting before hitting the red button, they're stuck with a standard, jittery 30-frames-per-second clip. Honestly? That's not true at all. You can actually fix it after the fact, though there are some "gotchas" regarding frame rates that most tech blogs totally ignore.
Learning how to make a video slow motion on iPhone isn't just about sliding a bar in the Photos app. It’s about understanding what your hardware is actually capable of doing. If you try to force a video shot at a low frame rate into slow motion, it’s going to look like a choppy PowerPoint presentation. We need to talk about why that happens and how to avoid it.
The built-in way (and why it’s kinda limited)
Apple makes things easy, mostly. If you already shot the video using the "Slo-mo" mode in your camera app, you've got it made. You just open the video in the Photos app, tap Edit, and you'll see a row of vertical white lines at the bottom. These lines represent the timing. Where they’re bunched together, the video plays at normal speed; where they’re spaced out, the magic happens.
But what if you didn't use Slo-mo mode?
This is where people get tripped up. If you took a "regular" video, the Photos app doesn't just give you those magic timing lines. You have to use iMovie or a third-party tool. In iMovie, you drop your clip onto the timeline, tap it, and hit the speed icon—it looks like a little speedometer. You can drag the slider toward the turtle. It works. But—and this is a massive but—it’s going to look "ghostly" if you go too slow because the iPhone has to "invent" frames that aren't there. This is what engineers call frame interpolation. It’s basically the phone guessing what happened between two frames. Sometimes it’s smart. Often, it’s a blurry mess.
Why 60fps is your best friend
Frame rate is everything. If you want high-quality slow motion, you need to be shooting at 60fps (frames per second) or higher. Standard video is 30fps. Cinema is 24fps. When you slow down a 30fps video by half, you’re down to 15fps. The human eye starts seeing individual frames at that point. It’s not smooth. It’s painful.
Go into your Settings. Tap Camera. Tap Record Video. If you have a relatively modern iPhone—say, an iPhone 13, 14, or 15—you’ll see an option for 4K at 60fps. Switch to that. It takes up more storage, sure. But it gives you the flexibility to slow things down by 50% in post-production without losing that buttery smoothness.
The Slo-mo mode specs
Apple’s dedicated Slo-mo mode usually shoots at 120fps or 240fps. At 240fps, you can slow things down to 1/8th of the original speed. It’s incredible for capturing water droplets or a skateboard trick. However, keep in mind that shooting at 240fps usually drops your resolution to 1080p. You’re trading detail for time.
Using the Reels and TikTok workaround
A lot of people don't realize that social media apps have better slow-motion "engines" than the native Photos app for standard videos. If you upload a regular 30fps video to Instagram Reels and use their speed tool to go 0.5x, their servers use a slightly different rendering process. It still won't look as good as native 120fps, but for a quick story, it’s often "good enough."
Just don't expect it to look like a Nike commercial.
Honestly, the best third-party app for this is CapCut. It has a feature called "Smooth Slow Motion." Instead of just repeating frames, it uses optical flow. This is a heavy-duty AI process that analyzes the movement of pixels. If you’re trying to figure out how to make a video slow motion on iPhone for a professional-looking edit, CapCut is currently beating iMovie in the quality department for post-processed slow-mo.
Lighting is the secret enemy
High frame rates require a ridiculous amount of light. Think about it. If you’re shooting at 240fps, the shutter is only open for a fraction of a millisecond for each frame. If you try to shoot slow motion in a dimly lit living room, the video is going to be incredibly grainy. Or it might flicker.
That flickering? It’s not your phone breaking. It’s actually your light bulbs. Most LED and fluorescent lights pulse at a frequency that is invisible to the eye but very visible to a high-speed camera. If you want that crisp, professional look, go outside. Sunlight is the only way to get truly clean high-speed footage on a mobile sensor.
Converting standard video to slow motion: Step-by-step
Let's say you have a video of your kid's first steps. It was shot at normal speed. You want to emphasize the moment.
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- Open the iMovie app on your iPhone. It’s free. If you deleted it to save space, go get it back.
- Start a new "Movie" project and select your clip.
- Tap the clip in the timeline so it's highlighted in yellow.
- Look for the Speed tool (the speedometer icon).
- Drag the slider toward the turtle. Start with 1/2 speed.
- If it looks choppy, iMovie is struggling. If you have an iPhone 15 Pro, you might have better luck using the "Cinematic" mode settings to adjust focal depth simultaneously, which hides some of the frame-rate jitter.
- Export the video in the highest resolution possible.
What about the "Action Mode" factor?
If you're running while filming, you're probably using Action Mode. This uses a heavy crop to stabilize the image. Be careful combining Action Mode with slow motion. Because Action Mode already needs a lot of light and crops the sensor, adding a high frame rate on top of that can make the image quality fall off a cliff. Use one or the other unless you're in direct high-noon sunlight.
Professional nuances: Shutter speed and motion blur
Real cinematographers use the "180-degree rule." This basically means your shutter speed should be double your frame rate. The iPhone handles this automatically, but it tends to favor a very fast shutter in bright light. This is why some iPhone slow-mo looks too sharp—almost clinical. There’s no motion blur.
If you’re serious about this, look into an app called Blackmagic Cam. It’s free and gives you manual control over the shutter angle. It allows you to shoot "standard" video with specific intent, making the transition to slow motion in your editing software look much more organic.
Practical Next Steps
Check your settings right now. Most people leave their iPhone on "1080p at 30fps" because it’s the default. Change it to 4K at 60fps if you have the storage space. This single change ensures that every single video you take for the rest of the year can be turned into a high-quality slow-motion clip later if you decide the moment deserves it.
Also, try this experiment: take a video of a running tap in standard 30fps and then in the 240fps Slo-mo mode. Look at the difference in the water droplets. Once you see the detail you're missing, you'll start using the dedicated Slo-mo mode for anything involving fast movement. Just remember to move the "timing bars" in the edit screen to choose exactly when the slow-down starts and ends. Precision is what makes it look intentional rather than accidental.