Codecs
What are codecs?
A codec is a device or program capable of performing encoding and decoding on a digital data stream or signal. The word codec may be a combination of any of the following: 'Compressor-Decompressor', 'Coder-Decoder', or 'Compression/Decompression algorithm'.
Codecs (in the modern, software sense) encode a stream or signal for transmission, storage or encryption and decode it for viewing or editing. Codecs are often used in videoconferencing and streaming media applications. A video camera's ADC converts its analog signals into digital signals, which are then passed through a video compressor for digital transmission or storage. A receiving device then runs the signal through a video decompressor, then a DAC for analog display. A "codec" is a generic name for a video conferencing unit.
An audio compressor converts analog audio signals into digital signals for transmission or storage. A receiving device then converts the digital signals back to analog using an audio decompressor, for playback.
The raw encoded form of audio and video data is often called essence, to distinguish it from the metadata information that together make up the information content of the stream and any "wrapper" data that is then added to aid access to or improve the robustness of the stream.
Most codecs are lossy, in order to get a reasonably small file size. There are lossless codecs as well, but for most purposes the almost imperceptible increase in quality is not worth the considerable increase in data size. The main exception is if the data will undergo more processing, especially editing, in the future, in which case the repeated lossy encoding could degrade the quality of the eventual file too much. Using more than one codec or encoding scheme throughout processing can also degrade quality but there are many situations where this cannot be avoided.
Many codecs are designed to emphasize certain aspects of the media to be encoded. For example, a digital video (using a DV codec) of a sports event, such as baseball or soccer, needs to encode motion well but not necessarily exact colors, while a video of an art exhibit needs to perform well encoding color and surface texture. There are hundreds or even thousands of codecs ranging from free ones to ones costing hundreds of dollars or more.
Many multimedia data streams need to contain both audio and video data, and often some form of metadata that permits synchronization of the audio and video. Each of these three streams may be handled by different programs, processes, or hardware; but for the multimedia data stream to be useful in stored or transmitted form, they must be encapsulated together in a container format.
While many people explain that AVI is a codec, they are incorrect. AVI (nowadays) is a container format, which many codecs might use (although not to ISO). There are other well known alternative containers such as Ogg, ASF, QuickTime, RealMedia and MP4.
Some Codec Sources:
DivX - www.divx.com
Codec Guide - www.codecguide.com
SMIL
When your streaming presentation contains multiple clips—such as a video and streaming text played together—you use Synchronized Multimedia Integration Language (SMIL) to coordinate the parts. Pronounced "smile," SMIL is a simple but powerful markup language for specifying how and when clips play.
The following are links to information on authoring SMIL 2 presentations for RealOne Player or RealPlayer 10. For information on authoring SMIL 1.0 presentations for RealPlayer 8, please consult the RealSystem Production Guide 8.
Learn more about SMIL
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Alternative Media Players
