From the website:

libdvdcss is a simple library designed for accessing DVDs like a block device without having to bother about the decryption.

This repository hosts the compiled libdvdcss-2.dll for Windows. Download the .dll from this repository and drop it into the Handbrake installation folder to convert your DVDs to mp4 files.

• Pick the version of libdvdcss you want (the highest version should be fine).
• Download the appropriate libdvdcss-2.dll from this repository.
• Move libdvdcss-2.dll into the Handbrake installation folder (usually C:\Program Files\HandBrake).
• Enjoy ripping your DVDs. Please use responsibly.

Either Linux, macOS, or Windows 10 is required.

These instructions are tailored for those familiar with the command line on a Linux machine. I documented them so I don't forget them.

Download the libdvdcss source code.

For Windows 10:

• Open the Ubuntu VM built into Windows 10 (Windows Subsystem for Linux).
• cd to the directory the source code was downloaded to (the path to your Downloads folder in the Ubuntu VM is /mnt/c/Users/<username>/Downloads).

Run the following to build libdvdcss-2.dll:

# macOS
brew install mingw-w64

# Windows 10 and Ubuntu
sudo apt-get install mingw-w64

tar -xjf /path/to/libdvdcss.tar.bz2
cd /path/to/libdvdcss

# 32-bit
./configure --host=i686-w64-mingw32

# 64-bit
./configure --host=x86_64-w64-mingw32

make
# .libs/libdvdcss-2.dll

# Run 'make clean' before compiling again.

If you get an error like WARNING: 'aclocal-1.15' is missing on your system.

touch aclocal.m4 Makefile.am Makefile.in

cp -R <version>/ dist/libdvdss-dll-<version>

Create a .tar.gz archive:

tar -czf dist/libdvdcss-dll-<version>.tar.gz dist/libdvdcss-dll-<version>/

Create a zip archive:

zip -r dist/libdvdcss-dll-<version>.zip dist/libdvdcss-dll-<version>/