Ok kids here is why you cant just play back your slow mo videos in iphoto or quicktime the way they play on the phone. The video is recorded at 240 FPS or 120 FPS when you import into iphoto the movie no longer has the meta data to slow it down like the camera app has on the iphone where you can select where the slow mo begins and ends, instead iphoto or quicktime just plays it back at its native FPS 240 or 120. If you want to preserve the slowmo settings you did on the iphone there are two easy ways to go.
1.
Use Apple’s free iMovie app on the iphone to first open the movie, edit it, and then save it as a new video, you don't really have to make any edits just saving a new copy does it. The new file will retain the slow motion, and can be viewed on your computer as such after you import the new copy. The new video now plays at 30 fps with the slowed down part intact. I guess the meta data is shared from iphone camera roll app to imovie app and then the new video is created with some behind the scenes conforming, interloping, trickery going on. It's magic 🙂
http://www.digitaltrends.com/mobile/how-to-create-slo-mo-video-on-an-iphone-6-an d-6-plus/
2.
Record your slow mo movie into a new feature in Yosemite that allows you to record what ever is going on on your iphone screen into a quicktime movie on your mac in real time.
Plug in your iphone to your mac, launch quicktime and there is a new option to record your iphone screen, below is a link on how to do it. It is the same as recording a screen capture video in quicktime but its capturing your iphones screen and re recording the video at a steady 30fps as your iphone does the regular to slow to regular frame rate transition. Great for recording games too into movies off your iphone and many other uses.
And as mentioned before you can email the video to yourself if it's not too big and upload to youtube and the slow mo stays intact because the video is again converted into a new video.
http://www.tekrevue.com/tip/record-iphone-screen-quicktime/
If you use FCPX you can import the video and it will be a 60 fps video as FCPX does not have a sequence setting of 240 or 120 but it does stay the same length at 60fps.
You can then slow the footage down with the retiming function and then export it but it wont have that ramp down and ramp up unless
you do some tinkering and editing using the retime to 0 option etc. This method you are creating the speed change from scratch though.
But it will be exactly where you want it to happen.
Most likely you can do this in the mac imovie app as well but I don't use it.
Hope this helps.