|Audio editing in QuickTime|
Edited audio can be saved it to iTunes as AAC (Apple's version of an MP3) using the Export option, if you really need it to be an MP3, iTunes can convert audio files to MP3 if you need it to.
Editing Video is magnificent as well, you can trim the video just as you a would audio, (which incidentally is exactly the same on any iOS device, same conventions). But where it really rocketh is in it's accuracy with splitting and deleting bits of video, or moving them around.
Just choose View > Show Clips to reveal a simple editing timeline at the bottom, click to select it (it will have a yellow outline) then move to the section of the video you want to split, you can even nudge the split point frame by frame using the arrow keys.
Once you've found the split point just choose Edit > Split Clip (or command Y) and you will see the video split into two (or more, if you split more than once) lozenges. Those bits can be deleted, or even moved about, simple.
When you're finished Export and choose the video kind you want.
For a final phenomenal feature, got video that is to big? No problem in QT Player, just choose export, then iPod touch (or iPad) from the drop down menu to create a smaller, web friendly version of your video.
(Via Tony Canales) if you want to do a screen recording, but ONLY record internal audio, NOT the ambient sound in the room, there is a free App called Soundflower. Once you add it, you can take screen recording with the internal audio only.