We have several ways to do it, including iMovie, which brings back the original speed on slow-motion videos and third-party apps.
Download the iMovie App
Download the iMovie and add the video to edit. Click on the speedometer to adjust the speed of the video.
Speedometer settings in iMovie
Drag the slider to control the speed and remember that every time you speed up the video it gets multiplied by 2X.
Splitting the Video
If you wish to add different speeds for the different lengths of video, cut the video into clips and adjust the speed by using the slider.
Speed up a Slow-Motion Video
To speed up a slow-motion video, go to the slo-mo section in the Photos app, select the video and click on edit.
Nullify the Slo-Mo
The video timeline is displayed on the screen using vertical bars, closely spaced bars represent normal speed and widely spaced ones represent the slow-motion video.
Edit and Save the Final Video
Drag the ends of the widely spaced videos to nullify the slo-mo effect on the videos, now tap on done to save the video.
Using the third-party apps
We can use many third-party apps like Video joiner and trimmer, Slow Fast Motion Video Editor, Video Speed Editor Slow and Fast, and SloMo Video Editor.