What actually makes an MP4 large
Duration, resolution, bitrate, and how much motion or detail the footage contains drive file size, not the fact that it is wrapped in an MP4 container. A short screen recording and a long 4K clip can both be MP4s at very different sizes.
The QuickCompress workflow
Choose the MP4 file, choose the outcome you want, a smaller file, or a specific target size, then compress locally on your Mac. Once it finishes, use the smaller output file wherever the original was too big to go.
When a target size helps
If there is an exact limit you are working against rather than just "smaller", target-size mode lets you enter that number directly. See how to compress a video to a specific file size, or the target-size hub for the common starting points.
What stays the same
The output is still an MP4, encoded locally with Apple Silicon hardware acceleration. Your original file is left in place; the compressed version is always a separate file.
Frequently asked questions
Will compressing my MP4 change its file format?
No. The output stays an MP4. Only the encoding settings change, to reach the size or outcome you chose.