To slow down a video on an iPhone, you have several effective methods:

1. Using the Photos App (for Slo-mo videos)

• Open the Photos app and select a video recorded in Slo-mo mode.
• Tap Edit in the top right corner.
• Under the video timeline, you'll see white vertical lines indicating speed changes.
• Drag the larger white bars to adjust where the slow-motion effect starts and ends.
• You can also trim the video length here.
• Tap Done to save your changes

Note: This method works best for videos originally recorded in slow motion.

2. Using iMovie (for any video)

• Open the iMovie app (free from the App Store if not installed).
• Tap Start New Project and select Movie.
• Choose the video you want to slow down and tap Create Movie.
• Tap the video clip in the timeline, then tap the Speedometer icon.
• Drag the speed slider to the left to slow down the video.
• Tap Done , then tap the Share icon and select Save Video to export it back to your Camera Roll

3. Using Third-Party Apps

Apps like Videoshop , SlowMoVideo , and FilmoraGo allow you to slow down videos with more control and effects:

• Import your video into the app.
• Use the slow-motion or speed control feature to adjust playback speed.
• Save the edited video to your iPhone

Additional Tips

• For the smoothest slow motion, record videos at a higher frame rate (e.g., 120fps or 240fps).
• Slowing down normal-speed videos may reduce quality or cause choppiness.
• Audio will also slow down with the video, which can affect sound quality

In summary, for quick edits on existing slow-motion videos, use the Photos app. For slowing down any video, iMovie is a straightforward built-in tool. For advanced control, third-party apps are available.