ALSA (an acronym for Advanced Linux Sound Architecture) is a Linux kernel module that replaces several different kernel drivers for sound cards with a single driver which handles the diversity of sound cards internally. It replaces all older sound drivers for the Linux kernel, notably the Open Sound System (OSS).
... this way, they were able to impose whatever restrictions they chose on the playback of such movies. See also DIVX for a more draconian and less commercially successful ...