You've probably been there. You're at a wedding, or maybe watching your dog do something marginally athletic, and you whip out your phone to capture that cinematic, "Matrix-style" moment. Then you play it back and it looks... choppy. Or dark. Or just weirdly artificial. Knowing how to make video slow motion iPhone isn't just about hitting a button; it’s about understanding the weird physics of light and frame rates that Apple’s marketing usually glosses over.
Most people think slow motion is a post-production trick. It isn't. Not really. On an iPhone, true slow motion is born in the sensor the moment you hit record. If you mess up the capture, you can’t really "fix" it later without things looking like a blurry mess.
The basic way to make video slow motion iPhone (and why it’s limited)
The most direct route is the Slo-mo mode in the native Camera app. Open the app, swipe past Video, and there it is. By default, most modern iPhones (like the iPhone 15 or 16 series) will toggle between 120 fps and 240 fps.
Here is the thing about frames per second (fps). Standard video is usually 30 fps or 24 fps. When you shoot at 120 fps and play it back at 30 fps, you are effectively stretching one second of real-time into four seconds of screen time. If you go up to 240 fps, that same second becomes eight seconds. It’s a massive jump.
But there’s a massive trade-off nobody mentions. Light.
To capture 240 frames in a single second, the shutter has to open and close incredibly fast. We are talking tiny fractions of a second. This means the sensor has almost no time to drink in light. If you try to use the 240 fps setting indoors under standard LED bulbs, you're going to see a horrific flickering effect. That’s because the camera is literally "seeing" the electricity pulse through your light bulbs. Stick to 120 fps indoors, or better yet, only use 240 fps when you are outside in high-noon sun.
Changing the speed after you’ve already shot the clip
Sometimes you forget to switch modes. It happens. If you shot a regular video and now want to know how to make video slow motion iPhone after the fact, you’re looking at software interpolation.
Apple’s Photos app lets you do a basic version of this.
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- Open the video.
- Tap Edit.
- Look for the vertical bars at the bottom.
In a native Slo-mo file, these bars tell the phone exactly when to start the slow effect and when to speed back up. But if you have a "regular" video, you won't see those bars. You'll need to use an app like iMovie or CapCut. These apps use a technique called "Optical Flow." They basically guess what the frames between your actual frames would look like. It’s clever tech, but if the movement is too fast, you’ll see "ghosting"—where your subject looks like they have three blurry arms.
The secret of the "Action Mode" and slow motion
Apple introduced Action Mode a couple of generations ago to compete with GoPro. It uses a heavy crop on the sensor to stabilize shaky footage. Many users try to combine this with slow motion. Don't.
Action Mode already requires a ton of light because it uses the Ultra Wide lens (which has a smaller aperture than the main lens). When you stack the light requirements of slow motion on top of the light requirements of Action Mode, your video quality drops off a cliff. It gets grainy. It looks like it was filmed on a potato from 2008. If you want a slow-motion action shot, use a gimbal or just keep your elbows tucked into your ribs to stabilize manually.
Why 4K Slo-mo is a trap for some users
If you go into Settings > Camera > Record Slo-mo, you'll see options for 1080p at 120 fps or 240 fps. On newer Pro models, you might see 4K options.
High resolution sounds great. Who doesn't want 4K? Well, your storage doesn't. A one-minute slow-motion video at 240 fps in 4K is a digital behemoth. It will eat your iCloud storage for breakfast. Honestly, for most social media uses, 1080p at 120 fps is the "Goldilocks" zone. It’s sharp enough for a phone screen, keeps the flickering to a minimum, and won't make your phone overheat after three minutes of filming.
Pro-level control with Third-Party Apps
If you’re serious about how to make video slow motion iPhone, the native app is actually kind of frustrating because it decides the shutter speed for you. Apps like Filmic Pro or Blackmagic Cam (which is free and incredible) let you lock your shutter speed.
There’s a rule in cinematography called the 180-degree shutter rule. Basically, your shutter speed should be double your frame rate. If you're shooting at 120 fps, your shutter should be 1/240. The iPhone's native app often cranks the shutter much higher to compensate for bright light, which makes the slow motion look "staccato" and choppy rather than smooth and dreamlike. Using a manual app allows you to fix this, though you might need a Physical ND filter (basically sunglasses for your camera) to keep the image from blowing out.
Fixing the "Flicker" problem
We touched on this, but it deserves its own space because it ruins more slow-mo videos than anything else. North American power grids run at 60Hz. European and many Asian grids run at 50Hz.
When you film slow motion, your frame rate might clash with the pulse of the lights. If you see black bands moving across your screen:
- Turn off the overhead lights.
- Move closer to a window.
- Switch from 240 fps down to 120 fps.
- In some apps, you can change the frequency to 50Hz to match the local power grid, which helps sync the "pulse."
Using Cinematic Mode for "fake" slow motion
This is a bit of a "hack." Cinematic Mode (which adds the blurry background) is limited to 30 fps or 24 fps. You cannot shoot a native "Cinematic Slo-mo" yet. However, you can shoot in Cinematic Mode at 30 fps and then use a video editor to slow it down by 50% using AI frame interpolation. This gives you that shallow depth-of-field look with a slow-motion feel. It’s not perfect, but for a dramatic b-roll shot of a person walking, it looks way more professional than the standard Slo-mo mode.
Practical Steps for your next shoot
Don't just point and pray.
First, clean your lens. It sounds stupid, but slow-motion footage highlights every smudge because the light is already being pushed to its limit. Use a microfiber cloth.
Second, lock your focus. Tap and hold on the screen until you see "AE/AF LOCK." In slow motion, if the camera starts hunting for focus, the resulting "pulse" in the blur is incredibly distracting when slowed down.
Third, move the camera. Slow motion looks best when there is both "subject" movement and "camera" movement. If you're standing still filming a waterfall, it's okay. If you're slowly tracking the camera sideways while the waterfall is crashing, it looks like a movie.
Managing the file sizes
Once you've mastered how to make video slow motion iPhone, you’ll realize your "Recents" folder is a graveyard of 500MB files.
Go into your Photos settings and ensure "Optimize iPhone Storage" is on if you're low on space. But more importantly, once you're done with a slow-mo clip, consider "Baking" the speed. If you export the video from an app like iMovie at the speed you want, it becomes a standard 30 fps file. This is often much smaller and easier to share on WhatsApp or Instagram, which tend to butcher the metadata of "live" slow-motion files anyway.
Summary of Actionable Insights
- Check your lighting: Never use 240 fps indoors unless you have professional studio lights. Stick to 120 fps to avoid the "flicker."
- Lock your focus: Avoid the "focus hunt" by long-pressing the subject before you hit record.
- Storage management: Use 1080p for casual clips. Reserve 4K slow motion for projects you intend to edit on a computer.
- Manual Control: Download the Blackmagic Cam app if you want to control the shutter speed and get that "motion blur" look that the native app lacks.
- The Edit: Use the "Edit" function in the Photos app to trim the slow-motion section. Only the part between the wide-spaced white lines will play in slow motion; the rest will be normal speed. This creates a much better "impact" for the viewer.
To keep your workflow clean, always reset your camera to "Video" mode when you're done. There is nothing worse than trying to capture a quick, spontaneous moment later on and realizing you're still in Slo-mo mode, resulting in a giant file of something that didn't need to be slowed down in the first place.