You can use Movie Editor for Mac It allows you to trim video clips, add scene transitions, crop video frame, customize output parameters and so on.
For more information and free download from:
http://www.formacdownload.com/Video-Editor-for-Mac-349.html
If you want to trim, crop, merge, watermark video clips and adjust video effects.
I recommend you this iFunia video Converter. in the while, you can use this program to convert all the popular video format.
http://www.ifunia.com/video-converter-mac.html
You may try this Video Editor for mac, it's a nice video editing software that can help you edit, join, split, trim, crop, convert and cut video, my friends recommend it to me, it's easy to use and works pretty well for me, it embeds many special effects. I had made a video with it and the video got award, that's pretty cool. Here is the free download link.
http://www.macvideoeditor.com/
Hope it helpful.
