Audio and Video Codec

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What is codec?
Codecs are compression technologies and have two components, an encoder to compress the files, and a decoder to decompress. There are codecs for data (PKZIP), still images (JPEG, GIF, PNG), audio (MP3, AAC) and video (Cinepak, MPEG-2, , VP8). There are two kinds of codecs
1. Lossless
2. Lossy

Lossless and Lossy Codec:
Lossless codecs, like PKZIP or PNG, reproduce the same exact file as the original upon decompression. There are some lossless video codecs, including the Apple Animation codec and Lagarith Codec, but these can’t compress video to data rates low enough for streaming.
In contrast to lossless codecs, lossy codecs produce a facsimile of the original file upon decompression, but not the original file. Lossy codecs have one immutable trade-off–the lower the data rate, the less the decompressed file looks (or sounds) like the original. In other words, the more you compress, the more quality you lose.

Audio Codec:
since most video is also captured with audio, the audio component must also be addressed. The most widely used audio format for acquisition and editing is PCM, which stands for Pulse-code Modulation, which is usually stored in either WAV or AVI format on Windows, or AIFF or MOV on the Mac. PCM is considered uncompressed, so it may be more properly characterized as a file format, rather than a codec. To preserve quality, most intermediate codecs simply pass through the uncompressed audio as delivered by the camcorder.
Most delivery formats have an associated lossy audio codec, like MPEG audio and AC-3 Dolby Digital compression on DVDs. Most early streaming technologies, like RealVideo and Windows Media, had proprietary audio components, so RealAudio accompanied RealVideo files, as did Windows Media Audio with Windows Media Video.
This dynamic changed most prominently when Adobe paired the VP6 codec with the MP3 audio codec for Flash distribution. The standards-based audio codec for video is the Advanced Audio Coding (AAC) codec, while WebM pairs the VP8 codec with the open-source Vorbis codec.

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