I found a way to reduce the file size by as much as several gigs without reducing resolution or any loss of quality. After upscaling, re-encode with HandBrake, choose the settings that works best for you. Re-encoding can reduce the file size by more than half depending on the settings you choose.
First, thanks for bringing up other software such as Handbrake and how it may reduce the size of files and has many options to choose from as well as settings. Second, we got to be really careful when talking about measures of such files.
When a service streams to you a 4k movie, it is not the size of the file(s) that make up a 4k movie on a disc you buy of a movie that is 4k (UHD). So how can two 4k offering be so different in size? Answer - some detail is lost and, often th compression used may have tricks to avoid redundant information such as areas of an image that remain static. The truth is the streaming version is not as good as the disc. This is not my opinion but a fact.
Handbrake more often than not is reducing a file which is in fact "lossee" meaning data has been lost from the original that it came from. While it may be possible to compress some data slightly (media files), you are already coming from a compressed file on the disc. Compresson on top of compression is in fact, missing info/detail found in the original disc.
Perhaps a better way to state things is that one might be able to compress a movie file, have the same resolution and be visually acceptable or no perceived loss of detail.
