Editing Codec (section)

==Compression==
{{Further|Image compression|Video coding format|Audio coding format}}

In addition to encoding a signal, a codec may also compress the data to reduce transmission bandwidth or storage space. Compression codecs are classified primarily into [[lossy]] codecs and [[lossless]] codecs.

Lossless codecs are often used for archiving data in compressed form while retaining all information present in the original stream. If preserving the original quality of the stream is more important than eliminating the correspondingly larger data sizes, lossless codecs are preferred. This is especially true if the data is to undergo further processing (for example, [[editing]]) in which case the repeated application of processing (encoding and decoding) on lossy codecs will degrade the quality of the resulting data such that it is no longer identifiable (visually, audibly, or both). Using more than one codec or encoding scheme successively can also degrade quality significantly. The decreasing cost of storage capacity and network bandwidth has a tendency to reduce the need for lossy codecs for some media.

Many popular codecs are lossy. They reduce quality in order to maximize compression. Often, this type of compression is virtually indistinguishable from the original uncompressed sound or images, depending on the codec and the settings used.<ref>{{cite web |title=Audio quality of aac vs. mp3 vs. wma vs. ogg encoders |publisher=SoundExpert |url=http://soundexpert.org/ |access-date=2010-07-25 |quote=above 5.0 – all sound artifacts will be beyond threshold of human perception with corresponding perception margin}}</ref> The most widely used lossy data compression technique in [[digital media]] is based on the [[discrete cosine transform]] (DCT), used in compression standards such as [[JPEG]] images, [[H.26x]] and [[MPEG]] video, and [[MP3]] and [[Advanced Audio Coding|AAC]] audio. Smaller data sets ease the strain on relatively expensive storage sub-systems such as [[non-volatile memory]] and [[hard disk]], as well as [[write once read many|write-once-read-many]] formats such as [[CD-ROM]], [[DVD]], and [[Blu-ray Disc]]. Lower data rates also reduce cost and improve performance when the data is transmitted, e.g., over the internet.