Codecs transform data for storage or transmission. In traditional broadcasting, codecs convert analog to digital and vice versa. In computers, codecs compress video, images, and audio. Lossless codecs reproduce the original data, while lossy codecs lose varying degrees of information. MPEG-1 is used for VCDs and MP3 is a popular audio codec. MPEG-2 is high quality and used for DVDs. MPEG-4 has technical advances and better compression. Ogg codecs are free from patent restrictions. RealVideo is optimized for online streaming. Many codecs are available online, with built-in functionality to download needed codecs.
Codec stands for Coder-Decoder (some say Compressor-Decompressor) and is used to describe anything that transforms data into another form for storage or transmission, then changes it again for use.
In traditional broadcasting, a codec is a physical device that transforms analog video and audio data into digital form to be sent over the air. It is also capable of transforming the received digital information into an analog format.
In computers, a codec is used to compress video, images and audio into a more manageable size. Most use a lossy compression method, but some are lossless. Lossless codecs, such as MSU or Huffyuv, reproduce the original video exactly, with no subsequent loss if the video is re-encoded. Most common lossy codecs lose varying degrees of information, but can save significant amounts of space.
A lossy codec can be transformative, predictive, or a combination of both. The transformative type cuts the original picture or sound and quantizes it into a more efficient space, then encodes it. A predictive codec compares a block of known data with adjacent data and discards the excess information to save size. There are many types of codecs available, each trying to strike an ideal balance between information loss and file size. Other factors, such as openness and processor power required for decoding, are also important when considering which one to use.
The MPEG-1 codec is used for VCDs and contains the MP3 standard, the most commonly used audio codec. Support for MPEG-1 is staggeringly high, both among computers and consumer cinema devices. The quality is very high, though not as high as MPEG-2, and the file sizes for the videos are quite large. The MP3 audio standard has good compression through a number of codecs and is very popular as an audio encoding solution.
MPEG-2 is a very high quality standard used for DVDs. While the MPEG-1 codec only allows progressive scan, MPEG-2 also supports interlacing, allowing for better viewing for its size. While not the most advanced of the video codecs available, MPEG-2 is firmly entrenched due to its use as a standard for commercially available DVDs.
MPEG-4 is a step beyond MPEG-2. It has a number of significant technical advances and better compression techniques, can handle both interlaced and progressive scan video, and is widely supported. A number of popular online codecs derive from the MPEG-4 codec. These include DivX, 3ivx and XviD. Each of these have small deviations from the original MPEG-4 codec to give them better compression and functionality in certain situations.
Ogg Theora and Ogg Vorbis codecs are a pair of video and audio codecs respectively. They have high quality and good compression and are completely free from patent restrictions, which makes them popular among many developers. RealVideo is a video codec designed specifically for online streaming. While many codecs can be streamed, RealVideo and its sister codec RealAudio are especially optimized for PNA and Real Time Streaming protocols.
There are literally hundreds of codecs used online, and everyone has their own favorites for specific applications. Many programs, such as Windows Media Player, have built-in functionality to automatically search and download the codec needed to play a movie or audio file, eliminating the need for a user to actively find them. There are also several bundles available for download, which install the most common audio and video codecs at the same time.
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