Why is the MOV encoded video file many times bigger than original MP4?

Hi, I am trying to free up some space on my machine and have several versions of the same video files. A lot of it was shot with GoPro hence the original format is MP4. When I brought the files to FCP they were converted to MOV, some files being 10x bigger. I am assuming that I can get rid of them, unless I want to do more work on the FCP movie. There is no way the MOV file has more quality than the original recording, right?

Thanks

The .mov file is a ProRes file, that stores more data. It stores all the data for each and every frame. It holds up to generational transcoding very well. The original MP4 files are super highly compressed, only storing a small fraction of the data for each frame, using what is known as a Long-GOP compression format. Falls apart under generational transcoding quickly. If you keep the original MP4 files as archives, sure, you can simply use them again for another project. Nothing wrong with that.

As for quality, you only get the quality your camera recorded, nothing "adds" data to that, that's it. But ProRes is easier for CPUs to deal with than the complex Long-GOP compression format.

That makes sense. If I want to use those files again in a project, I can just encode in prores again.

Thanks