Here's how I do it:
1. In iPhoto, locate the icon of the CLIP you would like to trim.
2. Do NOT trim this CLIP in iPhoto. That would be a waste of time. Instead, drag the icon of the CLIP from iPhoto to the desk top.
3. Open the CLIP in the QuickTime Player. You should be able to do this by simply double clipping on the icon you just dragged to the desktop. [Note that I use version 10.2 of the QuickTime Player]
4. In QuickTime, click on the menu item Edit: Trim... The trim bar (scrub bar) will appear at the bottom of the screen. [It is the long horizontal bar showing a series of frames surrounded by a yellow border with handles on both sides.
5. Drag the handle on the left to where you would like the CLIP to start. Drag the handle on the right to where you would like the CLIP to end. Click on the play button on the left to see how your edit looks. Re-trim as necessary. When you are satisfied with the trim you've made, click on the yellow trim button at the right side of the scrub bar. The scrub bar will disappear, replaced by a standard video play/pause bar.
6. Click on file menu item, File: Export. A dialog box will appear. At the top top of the dialog box there is a field that says "Export As..." Rename the video file of the CLIP to a descriptive name. Make sure this name is new and different from the name of the video file you have just dragged from iPhoto onto the desktop. The next field is a drop down which identifies the location the newly edited CLIP will appear. I use "Desktop." At the bottom the dialog box, select Movie as the Format. Click on the Export button on the bottom left of this dialog box.
7. Now close out of Quick Time, [or select File: Close from the Quick Time menu]. A dialog box appears that asks "Do you want to save the changes made to document... Click on "Don't Save."
8. An icon for the newly edited CLIP with its new name will appear on the desktop (or wherever else you designated for the location in Step 6 above). Drag that icon to the iPhoto album you desire.
9. Icons for the unedited CLIP with the unedited name will appear both on the desktop and in the iPhoto album from which it came. Put both icons in the trash. You will never see the unedited CLIP again. If you don't want to trash the file, then don't send these older files to the trash.
10. At this point there are two identical versions of the CLIP with the same descriptive name. Drag the icon with the new descriptive name from the desktop to the trash. [Don't worry, this won't affect the identical clip that you previously dragged to the iPhoto album you previously used]. You are done, You now have the trimmed CLIP in iPhoto.
