Apple - How to export a slo-mo video with the slow motion intact and without losing quality?
The reason importing it directly onto your computer doesn't appear to work is due to the way the iPhone plays back slomo videos.
The video itself isn't shot in "slomo", so to speak. Rather, it's shot at 120 frames per second, a typically higher frame rate than normal video recording.
This is significant because if you were to playback that video at 30 fps, the videos would appear to be playing in smooth slow motion because there is 4 times the frames to display. So, when you playback a video the iPhone is converting the selected section of the 120fps video into 30fps, giving it the slow motion effect - the whole video COULD be watched at a normal speed with no problem. When you import the file onto your computer, it is just a 120fps video file - it doesn't know when or where to convert it to 30fps, which is why it appears as if it "lost" the slomo when really it's playing in its native 120fps.
You can easily restore that slomo effect with almost any video editing software by slowing down the video (to 30fps, or any other speed for that matter) , just as your iPhone would do - you just have to do it manually (which could be better in some cases).
Alternatively, you should be able to imessage your video from your phone to your Mac without any considerable quality loss.
Open iMovie, load your slow mo video in a project, no need for filters or text etc.
Now go to your export screen, select the upload button. Scroll down and select: "keep video" or "Save file". ( I have a dutch language phone so I'm not sure what the English text will be). Save in 720p.
When you connect your phone to the computer you can see it as an extra drive "Internal storage". Select it, go into the DCIM folder and select the subfolder. Mine is called: "947ugfff" but anyway it is not the folder where your foto's and vids are but the folder where the saved videos from iMovie go.
Drag and drop and you're done!
Finally I found the best solution for me. Tried to import via Final Cut X but I am not sure it makes sense. Next I imported slow motion video from my iPhone via USB cable and opened Preview app that comes with a Mac and imported from here! Totally worked and I got .mov files out that I could open in quicktime and click cmd i and it showed 120 frames per second.
Option that didn't work: 1. sending via airdrop from photos app on iPhone to Mac - the framerate is changed to around 40-60fps. 2. uploading the video to dropbox or pcloud changes the framerate to 30 fps. 3. exporting video from Photos on Mac mini and saving them to iCloud Drive and then downloading them on my Mac Pro to edit also changes the framerate in the file...!?
Kind regards Mark Barner