Use a USB cable to transfer your video to a Mac or PC using iPhoto or compatible PC application. When opening the file, you?ll find the slow-motion effect will play back in normal 30 frames-per-second. That?s because even though the footage was shot in 120fps, whatever application you use will play it back in 30fps. Even if you view the video in Quicktime, you won?t see it in slow-motion. However, you can utilize the Quicktime Movie Inspector to ensure the video was shot in slow-motion. Just use the key command ?Control I? to bring up the Inspector and you?ll see the video?s frame rate is 120.15 FPS. This is proof you?ve imported a slow-motion video.
You can then use iMovie, Final Cut Pro, Adobe Premiere, or other video editing application to set the parts of the clip you want in slow-motion. This is how you can maintain the highest quality in your movie clip. In iMovie, for example, you can choose the part of the clip you want in slow-motion by going to Clip > Slow-motion. In the setting you should use 25%, because 120fps is four-times faster than 30fps. In Adobe Premiere you?ll use Clip > Speed/Duration. In Final Cut you use the Change Speed command. Note that when changing the clip speed there may be some processing time before you can view it in real time. After saving your newly edited clips with slow-motion to your hard drive, you can then upload to your favorite social site,
iCloud, backup or import back into your phone.
And
this is from Apple Site.