I shot video of my brother-in-law over the weekend with the iPhone 6's 240fps mode - also available on iPhone 5S' as well- and then wanted to quickly upload it to YouTube or Vimeo to share.
The problem is under iOS (iOS8 too), the share sheet upload option apparently compresses the footage more than using the native YouTube Capture or Vimeo apps for iOS. But if you just go grab the video clip in your Camera Roll and try uploading to YouTube it doesn't have the slow motion "effect" applied.
My Workflow to Get Slow-mo Clips to the Web
I started by putting the slow-mo clip into iMovie for iOS, turning on the fade-in/fade-out options, choosing a theme which adds background music and then saved it back to the camera roll. Slow-mo settings still intact.
Then I used the aforementioned YouTube Capture and Vimeo apps to upload to each service.
Which service does a better job of compressing/presenting the video? (YouTube ads notwithstanding. I pay for a Vimeo Plus account for client videos.
Vimeo
https://vimeo.com/106834891
YouTube
https://youtu.be/U_Ff6HHQBFU
Make sure the "HD" option is set.
Can you tell the difference?