Haven't found any archiving functionality in Calibre by myself, so assuming it doesn't exist. I am right? How can I shrink the library size using Calibre without changing a books format?
The size would not reduce much as the major volume is the accrual books. If they are epub or amazon format then they are already compressed.– mmmmmmSep 25, 2019 at 4:57
Can you clarify the question? Do you want to reduce the total size in bytes of your Calibre library without changing what books are in it? Why do you think that archiving would help? Wouldn't it just reclassify the books as archived without changing the amount of space they take up?– user.SNov 8, 2019 at 15:25
A good start may be to hunt down unnecessary duplicates, i.e. books that are encoded in more than one different formats– PPCApr 18, 2020 at 14:09
Calibre does not provide any compression tools, but indeed one could use third party tools to compress files in the directory structure. The predominant files to target would be DJVU and PDF files. Using ImageMagick's convert utility, it is not difficult to do programmatic compression (write a script that recursively goes through the library directory structure and compresses all PDF files). Testing is important to ensure no loss of visual quality.
Note that the same thing can be done for video files using the ffmpeg utility. Works a dream.