Q: why can't I speed up video clips in iMovie for iOS?

Yep, I had the same problem, then I read this article in which the speeding up feature is for new hardware, like iPad Air or iPhone 5 S that allows us to record at 120 fps. I can't wait to try that!!

http://www.gottabemobile.com/2013/10/22/imovie-garageband-updated-ios-os-x/

Looking at the article you linked, this is all it actually says about video speed:

You can change speed on videos and even do picture-in-picture on iOS devices. The changing speed setting is great for iPhone 5s who can record slo-mo video at 120 frames per second.

As this states, you'd think that 120fps would be necessary to slow down video, otherwise it starts to look choppy. If you speed it up you're basically just dropping frames, right?  Still a mystery why we can't speed up in iMovie.

I am able to speed up clips with iMovie for iOS 2.0 on 64bit devices, like iPhone 5 S.

i have the new iphone 5c. I'm a bit miffed that this phone doen't support the speed up movie clip effect. What gives, Apple? I have kids, this effect is very much needed!!!!

The iPhone 5c is a 32 bit device, not a 64 bit, like an iPhone 5 S. You can also speed up clip in the new iPad Air.

More here:

http://www.idownloadblog.com/2013/10/22/redesigned-enhanced-and-64-bit-optimized -ilife-suite-now-available-on-ios-and-mac/

Hey!!! I had the same problem! I just spent time on the phone with a really helpful guy on apple supprt and he figured out for me that it  is because you have to edit the speed outside of your project.  You edit the speed of your video first, then start a new project and add the video into it!

So...I have an iPad 2-so I can't speed up clips??!!??!!?!?!?!??????This stinks Apple!!