
Without getting to far into the how to side of video editing, this post will remain a little simpler and just offer a friendly warning so others will not lose any video footage — like I did. Thankfully, in my case, the footage was not all that important, but still.
Anyway, getting back to the term edit, it seems that the iPhone more specifically does not edit video, but instead it actually trims the video. All in all, that is fine by me, but be prepared that when you make any edits, or trim that video on your iPhone that you are going to lose the parts you trimmed.
You see, when you trim the video it discards the trimmed portions and leaves you with just your edited version. What would be ideal, is if Apple would save the original file and then save a second (editing) version as a new file.
That said, think twice before you edit trim your precious videos on your iPhone 3GS because you may end up tossing that special moment.
article source: http://www.iphonefreak.com/2009/06/iphone-3gs-video-editing-and-a-friendly-warning.html