Poor video quality after iPhoto import

Hi all,

I used to make videos with my iPhone 4S for quite some time. Quality was always as expected.

Now I got an iPhone 5S and make even nicer high res videos. When I watch the vidoes on my iPhone quality is as perfect as it can be on a smartphone.

Now I import the videos to iPhoto. When I watch them in iPhoto (or edit them in iMovie) the quality is often awful! Sound lags, fragments, 'green screens', lots of pixels...

Any ideas to overcome this?

Thanks in advance,

Tobias

iPhoto 9.5.1