: Unpack the downloaded Bento4 SDK archive to a permanent folder on your computer (e.g., C:\Bento4\ ).
If you have the correct decryption key, the process is straightforward:
: Navigate to the \bin folder inside the extracted directory. You will find mp4decrypt.exe listed there. Add to System PATH (Optional but Recommended) :
mp4decrypt --key 1234567890abcdef1234567890abcdef:fedcba0987654321fedcba0987654321 input.mp4 output.mp4