… for Codecs & Media
Tip #348: Codecs – Explained (Part 2)
Lossy is smaller, Lossless is better
As we learned in Tip #347, there are two types of codecs: lossless and lossy. In this tip, I want to explain the difference. For this, we’ll turn to a Wikipedia article.
Lossless codecs are often used for archiving data in a 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. 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 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 formats such as CD-ROM, DVD and Blu-ray Disc. Lower data rates also reduce cost and improve performance when the data is transmitted.