When you export a video file in Apple’s QuickTIme Player or iMovie, does the resulting file size leave you confused? Maybe you have had the same experience as read Rob Dlutek:
First, I took an MP4 file (90.4MB), trimmed it at the beginning and the end and exported to disk, lowering the resolution from 720p to 480p. The resulting file was 132.5MB! Then, I took the original file, trimmed it and saved it (Command-S) without making any adjustments to the size. The result: 88.8MB. That was close to what I expected, but the file was still way too big for using on the web.
Trimming a movie in QuickTime Player and saving it retains the trimmed video data, but marks the points to play. You can see this by playing the saved version in a non-Apple video player, like VLC, which ignores the trim marks.