What lowering the frame rate does
Frame rate is how many pictures make one second of video. Going from 60 to 30 fps keeps every other moment in time; motion looks slightly less fluid, but for talking, travel and most phone clips the difference is hard to notice on a small screen.
Frames are chosen by their timestamps rather than by count, so a clip that switches between 60 and 24 fps in dim light — common on phones — comes out at a steady 30 fps with exactly the same length and lip-sync.
How much space it saves
At the same picture quality, 60 → 30 fps typically saves 30–50%, not 50%, because neighbouring frames are similar and compress well. The tool encodes at the High quality level for the new rate, so most of the saving comes from the dropped frames rather than from blurrier ones.
Lowering the resolution saves more; for the smallest file, combine both with the Video Compressor.
Choosing the rate
- 30 fps: the standard for phones, social media and video calls.
- 24 fps: the cinema rate; good for footage meant to look filmic, poor for fast games.
- 15 fps: enough for screen recordings, slides and tutorials, where little moves.
The tool never raises the frame rate: adding frames would only duplicate pictures and make the file bigger. If the source is already at or below your choice, it says so.
Slow-motion and high-frame-rate clips
120 and 240 fps clips are stored at that rate, and phones mark a section to play slowly. Converting to 30 fps keeps normal-speed playback, but the slow-motion effect set in the Photos app won't come with it; slow it down in an editor first if you need it.