Accessing Music and Video

COMP1260 > Using the Internet

Introduction

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Codec

A codec is a device or computer program capable of encoding and/or decoding a digital data stream or signal. Codecs are used to encode a data stream or signal for storage, or decoding them for playback and editing. Codecs are a key component of audio and video playback, creation and distribution. In general raw audio and video is far too large for distribution and storage, for instance we need 118 Gb (or about 26 single layer DVDs) to store a raw video 90 minutes in length at VHS quality. To remedy this we use codecs to compress (encode) the data before it is stored or distributed. As a consequence any user who wishes to playback the media must have the same codec to uncompress (decode) the data.

Codec Types

There are two types of codecs:

• Lossy Codecs: Lossy codecs achieve compression by reducing the quality of the media by some amount, but employ some algorithm to give the impression of the data being there. Some examples of popular lossy codecs include: Mp3, Wma, and Mp4.

• Lossless Codecs: Lossless codecs achieve compression while retaining all information present in the original media. As a consequence of all the original information being retained, the media encoded are substantially larger then that of their lossy counterparts. Lossless codecs are generally preferred if the media is going to be put through further processing (ie editing), in which case the constant reprocessing on lossy codecs would cause the media to degrade in quality at each step. Some examples of popular lossless codecs include: FLAC, APE, and FFMPEG

Digital Audio

Digital Audio uses digital signals (binary) for reproducing sounds. As such, it is the representation used by modern computers to playback, record, and edit audio. Audio playback on a computer requires several steps; first, the file to be played is decoded using the appropriate codec to convert it into raw digital audio. Second, the raw digital audio is converted to an analogue signal inside the sound card of the computer. Third, the analogue signal is amplified and broadcast through the speakers or headphones connected to the computer.

Acquiring Media

One Type of Early Punch Cards

Further Readings

History of Operating Systems on Wikipedia: http://en.wikipedia.org/wiki/History_of_operating_systems
Computer History Timeline: http://www.computerhistory.org/timeline/?category=sl
Operating System Timeline: http://trillian.randomstuff.org.uk/~stephen/history/timeline-OS.html
Detailed Timeline of Non-UNIX Operating Systems: http://www.oshistory.net/metadot/index.pl?id=2165;isa=Category;op=show
Screenshots of Major Operating Systems: http://www.guidebookgallery.org/guis

References

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