You’ll see it appear at the end of the first file. Next, drag-and-drop another file onto the QuickTime window. Start by opening the first file in QuickTime. Quicktime can also combine multiple video files. Or, you can click File > Duplicate to create a duplicate copy of your edited video file and save the copy, preserving the unedited original. You can then click File > Save to save the video file, removing all the other content. Click Trim and the other bits of the file will be removed. A simple trimming interface will appear - just click and drag the bars on each end to select the part of hte video file you want to keep.
With the video (or audio) file open in QuickTime, click Edit > Trim. You can also open an audio file in quicktime - Command-click or right-click it, point to Open With, and select QuickTime.
QuickTime is the default video player, so you should just be able to double-click your video file. mp4 file or another video with QuickTime.
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