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

It can be controlled through environment variables:

LIBDVD_VERBOSE={0|1|2}: 
    0: no error messages, no debug messages,
    1: only error messages (this is the default)
    2: error and debug messages

LIBDVD_CACHE=directory:
    specifies an alternate directory in which to store title key
    values.  ~/.libdvd is the default.