Codecs and Architectures

Encoding is the process whereby media files are prepared for streaming over the Internet. The codec (compression/decompression) is an algorithm used to generate the streaming file. Although equally relevant to audio, this article discusses basic encoding architecture and codecs relating to streaming video.

The Basics
From the time a video is shot until the end user views the stream, the bits and bytes forming the streaming media are subjected to several different pieces of hardware and software. It is transformed from a moving picture on one end into a series of ones and zeros. The information is processed by several software programs and transferred through the Internet to the end users computer in the form of streaming video.

Encoding Hardware and Software
Streaming media begins with recorded content. The output of the camera is fed into video and audio capture board located in the encoding computer. These boards capture the camera's signal and transform it into a digital format, usually an AVI format (AVI, Audio Video Interleaved, is a standard computer video format).

AVI files are not typically used over the Internet for two reasons. 1. AVI files are usually very large. Depending on the capture process, an AVI can be more than one megabyte per second of video. 2. AVI files can't be streamed over the Internet. You must download the entire file before you can play it.

Once captured, the AVI file is fed into encoding software. The encoder uses a codec to convert it from an AVI file to a streaming format (i.e., Windows Media .ASF, Real's .RM, Apple's .MOV). Finally, the streaming file is uploaded to a server for delivery over the Internet.

Codec: short for compression/decompression
Codecs are mathematical algorithms created to allow media files to squeeze into a smaller streaming format for decoding by the end-user's player. Encoding software uses codecs for compressing the file. Decompression occurs during the viewing process on the end user's computer. The process is similar to zipping and unzipping a file on a PC.

Multibitrate Codecs
Multibitrate codecs allow several streams of different bitrates to be bundled into one file. The streaming server then communicates with the end user's media player to determine the optimum speed for delivery.