- A DVD decoder is a form of computer software that interprets the media on a DVD, which has been encoded and compressed to make it all fit on a single disc, so that it may be viewed on a computer equipped with a DVD drive or a stand-alone DVD player. Stand-alone DVD players come with the decoding software built in; computers need decoding software to be installed.
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Most commercially produced DVDs are encoded using a combination of MPEG-2 compressed video and various audio formats, many of them multi-channel. That's because while a DVD can hold a lot of data, it's not enough for an entire movie, plus all the bonus features and multiple audio tracks that typically come with the feature film---not to mention the copy protection most studios put on their DVDs to prevent users from making copies.
The process of compressing all this data so that it can fit on a single disc involves a complex set of algorithms that basically take analog data and represent it in a digital way. Quality is sacrificed during the encoding process, so when the data is played back it needs to be decoded, a process that essentially consists of an inversion of each stage of the encoding process. The software that does this, developed by engineers and mathematicians, is called "codecs," for enCOder/DECoder.
One form of decoding software interprets the compressed video. Another form of decoding software is necessary to unlock the copy protection most studios put on their DVDs to prevent users from making copies. Computers also require another type of decoder that allows the video images to be played through a viewing program installed on the machine. - Still other decoders are required to interpret the various audio tracks on a DVD; for example, Dolby Digital data requires a specialized Dolby Digital decoder, while DTS audio also requires a DTS decoder.
