Audio and Video Compression

Posted By BrokenClaw on April 1, 2008

Data compression is a function performed by computers to decrease the size of a data file, while controlling the amount of information that gets lost. The purpose of data compression is to reduce the amount of space required to store the file and to reduce the bandwidth required to transfer the file.

With audio files, especially music files, the degree of compression is very important to the clarity, richness, and dynamic range of the playback. The compression level of audio files such as MP3 are described in terms of kilobits per second (kbit/s), which is called the bit rate. The higher the bit rate, the lower the amount of compression and the better the quality, but the larger the file size.

Internet music files are often saved and transferred in a 96 kbit/s format, although 128 kbit/s produces a noticeable improvement in the quality of sound, similar to an FM radio broadcast. For orchestral or vocal music, 192 kbit/s is considered to be the minimal acceptable rate. Higher bit rates are generally indistinguishable from a digital CD recording.

With digital video files there are two distinct types of compression. The first type is video which is intended to be played directly over the Internet, in the same way that Internet radio plays audio. This type of video compression runs the full range from high quality video, like the TV shows shown on network websites, down to the highly compressed, low quality video clips like the ones shown on YouTube.

Low quality video is characterized by blurry blocks of color. The compression technique is similar to the one used in JPG photos, but the effect is even more exaggerated in video.

The second type of digital video is intended to be equivalent to, or better than, regular television programming. The idea with this type of video is to encode the files to a smaller size using compression algorithms, then allow the player in your home to de-compress or decode the file to its original quality. Digital cable and satellite TV are examples. It’s important to know that all high-definition TV is digital, but not all digital TV is high-def.

A more recent development in digital television is having movies and shows which you purchase and download over your broadband connection to play on your TV. Television which comes to you over the Internet is sometimes called Internet protocol television, abbreviated IPTV. Once again, to save on bandwidth, IPTV may be compressed.

With services like Verizon’s FIOs providing television service, the distinction between broadcast TV and IPTV is becoming blurred.

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