Your iPhone doesn’t truly slow down footage in post. It captures 120 or 240 frames per second, then plays them at 30 fps, stretching one second of action into four or eight. That high frame rate is why a slow motion video on iPhone looks so smooth—and why the files get big fast. This guide walks through the exact settings, shot prep, and compression steps to get pro results without filling your storage.
How do I shoot slow motion video on iPhone?
Open the Camera app, swipe to Slo-mo, and tap record. Before you shoot, go to Settings > Camera > Record Slo-mo and pick your frame rate and resolution. On iPhone 12 and later, you can shoot 1080p at 240 fps or 4K at 120 fps on many models. The 240 fps option stretches one second into eight seconds of playback; 120 fps stretches it into four. Start with 1080p/240 for fast action and 4K/120 for wider shots you may crop later. Your iPhone records audio at normal speed even during slow motion, so background sounds stay natural.
When you frame a slow motion video on iPhone, hold the phone steady for a beat before and after the action. Slow motion amplifies every micro-movement, so a tiny shake becomes a visible wobble. Use both hands, rest your elbows on a surface, or lean against a wall. If your shot involves motion, keep the subject moving across the frame rather than toward the lens. That lateral movement reads better in slow motion.
Choose the right frame rate for slow motion
Pick 240 fps for fast subjects, 120 fps for everyday motion and better resolution. The choice changes how much light you need, how big the file gets, and how much you can crop later.
| Setting | 120 fps | 240 fps |
|---|---|---|
| Best for | Pets, walking shots, vlogs, 4K detail | Fast action, sports, jumping, splashes |
| Playback stretch | 4x slower (1 sec → 4 sec) | 8x slower (1 sec → 8 sec) |
| Resolution | Often 4K or 1080p | Usually 1080p max |
| File size | Smaller than 240 fps | Larger, especially in bright scenes |
| Light needed | Moderate | A lot more |
If you already filmed a standard 30 fps clip and want to slow it down after the fact, adjust the playback speed instead of reshooting. Native slow motion captures more frames, but the speed tool works for existing clips. For precise speed ramps on your Mac, Apple’s iMovie user guide covers the process step by step.
Change the speedDo it on your video, here.Why does my slow motion footage look dark and grainy?
Because 240 fps gives the sensor only a fraction of the usual exposure time, so less light reaches it. At 240 frames per second, each frame gets 1/240s of exposure, compared to about 1/30s for standard video. That’s eight times less light, so your image gets dark and the ISO jumps, creating grain. Shoot outdoors in daylight or add a bright continuous light indoors. Avoid mixing dim lamps with high fps. Move closer to a window or turn on every light in the room. The 120 fps mode needs half as much light and is often the safer choice indoors.
Stabilization also suffers in low light because the camera may use shorter exposure and higher ISO, which amplifies shake. If your clip already has noise, brighten it before editing and keep the final output resolution modest. Grain makes files harder to compress, so cleaner footage also means smaller files after compression.
Compress slow motion files without losing detail
Trim first, then use a video compressor to shrink the file while keeping the high-frame-rate motion intact. Slow motion files are massive. A 10-second 1080p/240 clip can be 100 MB or more. Before you share, cut the moments you don’t need with a video cutter. Keeping only the peak action reduces file size by half or more. Then upload the trimmed clip to a video compressor and choose a target size or quality level. The compressor removes redundant data without visible loss, so your slow motion still looks smooth.
When compressing, keep resolution at 1080p unless you need 4K. High frame rates must stay at 120 or 240 fps inside the file, but the container can be compressed. MP4 with H.264 is the most compatible format for sharing. Klipa’s compressor produces an MP4 that plays on iPhones, Androids, and social apps without extra steps.
How do I share slow motion video without losing quality?
Compress to a compatible MP4, then share through the platform that suits your audience. After compression, your slow motion clip is small enough for email, Messages, or upload. For TikTok, Instagram Reels, or YouTube Shorts, convert the clip to a vertical 9:16 canvas with a video resizer. Social platforms often recompress your video anyway, so starting with a smaller 1080p file prevents double compression artifacts. If you want to adjust the feel of the slowed moment, you can fine-tune the speed after the fact, but keep changes to one pass to preserve maximum detail.
Quick Answers to Your Slow Motion Questions
How do I turn on slow motion on iPhone?
Open the Camera app and swipe left on the shooting modes until you reach Slo-mo. Tap the record button to start. Before recording, you can set resolution and frame rate in Settings > Camera > Record Slo-mo.
What fps is best for slow motion on iPhone?
Use 240 fps for very fast subjects like sports, splashes, or jumps. Use 120 fps for everyday movement, pets, or vlogs where you want higher resolution and less demand for light.
Can all iPhones shoot 240 fps slow motion?
No. iPhone 12 and later models generally support 240 fps at 1080p, while many older models top out at 120 fps. Check Settings > Camera > Record Slo-mo to see which options your model offers.
Why is my iPhone slow motion video so big?
Higher frame rates mean more frames per second of recording, so each second of footage holds much more data. A 240 fps clip can be several times larger than a standard 30 fps clip of the same length.
How do I compress a slow motion video on iPhone?
You can trim the clip first to remove unwanted sections, then use a free online video compressor to shrink the file. Klipa AI’s compressor keeps the high-frame-rate motion smooth while reducing size for sharing.
Can I change the speed of an existing video on iPhone?
Yes. If you already recorded a standard clip, you can adjust its playback speed with Klipa AI’s speed changer. Native slow motion captures more detail, but the speed tool works well for existing footage.
Does slow motion record sound on iPhone?
Yes. Your iPhone records audio at normal speed even while filming in Slo-mo. The sound stays in sync, but the visual motion plays back slower than real time.
How do I share slow motion video on TikTok without losing quality?
Trim the clip, compress it to a smaller MP4, and resize it to vertical 9:16 before uploading. Starting with a lean 1080p file helps avoid extra recompression artifacts on TikTok, Reels, or Shorts.
Slow motion video on iPhone becomes predictable once you match frame rate to the scene, add enough light, and keep the file lean. Shoot 240 fps for fast action, 120 fps for everyday detail, then trim and compress before you share. If you have a clip sitting in your Photos app right now, upload it to Klipa AI and adjust the video speed or compress it for social in under a minute.
