Export process and video size

Hi all,

My original video is 4K-30 fps and it’s size is 2,42 Go.
I do no modification at all, not a single cut, not a transition, strictly nothing. I just export the video with the same settings than the original : 3840 x 2160 (i.e 4K), and 30 fps.
It turns out that my output video size is 518 Mo.

How come while I didn’t change the resolution neither the fps?
While I put the original vs the edited next to each other, I cannot see any visual loss of quality while the size has shrunk for 5 times less --> What in the video have been reduced / compressed?

Can anyone explain what is the process behind exporting?
I read on other topics that Codec has something to do with it but I didn’t get it clear. The one set by default here is libx264, quality = 55% (crf = 23) ,GOP = 150 . I kinda guess the 55% quality means something, but again visually I cannot see any difference ( 45% quality loss would be very much noticed I suppose).

Some clarification would be much apreciated.
Thanks in advance.

There are various reasons how this could happen, see:

Download mediainfo (https://mediaarea.net/en/MediaInfo/Download), open both files (original and exported) on it, click on menu item View->Text take a screenshot and post it so we can compare the properties.

Welcome to the Forum, @Carlton, you have asked a simple question whose answer is, alas, not simple at all.

I was about to refer you to an explanatory thread which contains this…

…summary; however, I see that the author of that response has arrived ahead of me.

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