Codecs are required to encode audio and video files for transmission by reducing the file size, and hence the downloading time, and also to convert them back into a form suitable for replay. This article describes the types of codec available and the difference between them.
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Copyright 2006 Peter Nisbet
The word ?codec? is short for Coder/DECoder or Compressor/DECompressor. It is a technology used basically to render data suitable for transmission using a set of protocols which must also be used for its reception. MP3 is an example of a common codec. They can be applied in hardware, software or in a combination of both. This article is specifically about audio codecs. Video signals will be discussed in another article.
Audio data can be compressed, resulting in a file smaller than the original. How much smaller depends on the type of codec , and data can be lost, resulting in a reduction in audio quality. The type of codec where data is lost is called Lossy, while the other type where data is not lost is called Lossless.
Lossless codecs work rather like Zip files. In zip files, the data is compressed to take up less space. In fact a zipper is a lossless file codec: you use the zipping software to compress the data, then you subsequently required the zipping software to decompress it to a readable form. NO data is lost, and this is how a Lossless codec works. It compresses the data for transmission then decompresses it to replay it. The file is in exactly the same form when played as it was prior to transmission.
Examples of Lossless codecs are Monkeys Audio, WavePack and FLAK. This gives the best playback sound quality. Typical players are Media Center and Winamp. This type of file naturally requires a Lossless codec for play-back, so will not play on an MP3 player. The main problem with this type of audio format is that it compresses at best only to 4:1.
Where greater compression is required, Lossy codecs must be used. With this type of system, part of the file data is lost or discarded to allow the enhanced compression. Lossy codecs can compress audio files down to 10:1 which is a massive saving in storage requirements. The way it does this is to discards parts of the file it considers is not required by the human ear. For example, the maximum frequency the human ear can detect is around 16 KHz so frequencies above this are cut out. Some codecs go down ever further to 12 KHz.
Also certain sound combinations are discarded, such as soft sounds occurring immediately after harsh loud ones. The human brain tends not to distinguish these soft sounds, so they would not be missed if removed from the file. Once the audio file is decoded, it is not restored to the original size. Hence Lossy codec is more of a coder-decoder than compressor-decompressor.
Examples of Lossy audio formats are MP3, Musepack, OGG Vorbis, WMA (Windows Media Audio) and MP4. There are various codec encoders and decoder also available, though the average person generally has no choice since they are ready installed in the hardware being used. A description of the software which actually carries out the work is beyond this article, but there are three main types: constant, variable and average bit-rate encoders. Higher bit-rates give better sound quality, but larger file sizes. The development of Lossy technology has revolutionized the way we buy music from hardware to downloadable software, but this is another subject.
You may have to download a specific codec to be able to open certain audio and video files you have either purchased or downloaded. If you have purchased the file, the codec will generally come with it, but with a free download, you may also have to download the relevant codec. You will probably be informed what codec is required to decode or decompress it. You should then search for the codec using a search engine and you will probably find it on free download.
The next article will discuss how codecs work with audio-video files and how their developed has tremendously reduced the download time for movies to such an extent that downloading from the internet is now commonplace and proving a problem for the movie studios.