QuickTime X seems to be able to open a `.mp4` file, trim it, and re-save as `.mp4` with no re-encoding.

This was surprising to me, as the only way to `Export` the file is via a filetype change to `.mov`.

If you take other actions such as `Add Clip to End...`, the menu item for `Save` will become greyed out and you will be forced to export as `.mov` if you wish to save. If you `Split Clip` more than one time without deleting a segment it similarly prevents the save.

But this does enable easy trimming and re-saving without `.mov` conversion using Quicktime X.

### Trim .mp4 video file:

1. Open a `.mp4` with QuickTime Player X
2. Scrub to a location in the file. Use the keyboard arrow controls for frame-perfect accuracy.
3. Press `Split Clip` <KBD>CMD</KBD><KBD>Y</KBD> to cut the video into two segments.
4. Select the unwanted segment. Press <KBD>delete</KBD> to delete.

Note: You can also use the `Trim` <KBD>CMD</KBD><KBD>T</KBD> command. But I find it is almost impossible to accurately set the In/Out markers without keyboard arrow controls, which do not function in the Trim UI. Instead, use `Split Clip` to delete each end of the trim.

### Save without re-encoding

1. Press `Save` <KBD>CMD</KBD><KBD>S</KBD>
2. A "Save As..." dialog will pop up.
3. Note that it is exporting as `.mp4`. Default value: `Export As: Untitled.mp4`
4. Rename your file and save.
5. Resulting format will be same file type and dimensions as your source file. Its file size should also be smaller, depending on how much was trimmed.

[![Export As:][1]][1]

### Export As...

Note that the `Export As...` menu does **NOT** contain "pass through" or "original" or any good option.

When you select `480p` you are only able to export as a `.mov` file.

Use `Save` rather than `Export`, which will allow you to re-save as a `.mp4`.

[![Export As is NOT good][2]][2]


  [1]: https://i.sstatic.net/OyWSj.png
  [2]: https://i.sstatic.net/rPhTo.png