I can´t use .mov videos in Imovie11?

Well, I use a Video recorder to record my videos in a PC, then i put them in a Kingston USB, then, I copy them in Imovie11 by importing them using Import-Movies and then i select my .mp4 video from my USB. Everything it´s ok, but when I want to put Slow motion, I must optimize/convert the video and when I do it, The video gets frozen, and the audio is still playing, but it´s very annoying. Well, then I try finding the movie in the finder, and I see that now it´s a .mov file, and it doesn´t work using Quicktimeplayer So i´m very confused. What should I do? This happens with all my .mp4 videos, and I can work with them in Imovie, but I can´t add slow/fast motion and i want to do it.

I used Cmd-I in Quick time, and this is what it show me (In the .mov file that before was a .mp4 file):

Source:/Users/Fede/Movies/iMovie Events.localized/Montaje/ciudad antigua.mov

Format: Apple Intermediate Codec, 1.920 × 1.080

PCM lineal, 16 bit little-endian entero firmado, 48000 Hz, Estéreo (I D)

FPS:0

(FPS are 0, maybe this is the problem)

Now what I get in the original.mp4 video:

Source:/Users/Fede/Movies/iMovie Original Movies.localized/Consejirijillo 1/ciudad antigua.mp4

Format:H.264/AVC, 1.920 × 1.080

AAC, 48000 Hz, Estéreo (I D)

FPS:59,94

(The FPS are 0 vs 59,94, I think this is the problem, but How can I fix it?)

The Imovie version is the newest.

I don´t know what to do, so I come here for help 😉

Thanks

PD: Sorry about my bad english, I speak spanish so maybe something is in spanish