Video export file size smaller then original

Hi, I am joining two videos together in SHOTCUT. Each video is 30min long (12GB in size).
When I export my compiled video the exported size is not 2x 12GB (24GB), but 6,83GB only.
As pertaining the video quality it seems there is no loss (exported in 4K).

Should not the exported file be 24GB?
Am I doing something wrong?

Thank you for any help or explanantion.

Various factors affect the size of an exported video, one of the most common is “bitrate”. You should check the properties of the 3 videos, either using software like Mediainfo, or by opening them in Shotcut and clicking on “Properties”. If the video quality of the exported video is good, it could be that the quality of the originals was over-specified. Are you sure that the framerate is the same, e.g. your original footage was 60fps and you exported at 30fps. Without seeing the media info all you can do is guess.