VIDEO\/AUDIO CODEC

T&F

A video codec is a device or software that enables video compression and\/or decompression for digital video. The compression usually employs lossy data compression. Historically, video was stored as an analog signal on magnetic tape. Around the time when the compact disc entered the market as a digital-format replacement for analog audio, it became feasible to also begin storing and using video in digital form, and a variety of such technologies began to emerge.

Digital video codecs are found in DVD systems (players, recorders), Video CD systems, in emerging satellite and digital terrestrial broadcast systems, various digital devices and software products with video recording and\/or playing capability. Online video material is encoded by a variety of codecs, and this has led to the availability of codec packs - a pre-assembled set of commonly used codecs combined with an installer available as a software package for PCs.

Encoding media by the public has seen an upsurge with the availability of CD and DVD-writers.

A variety of video compression formats can be implemented on PCs and in consumer electronics equipment. It is therefore possible for multiple codecs to be available in the same product, avoiding the need to choose a single dominant video compression format for compatibility reasons.

Video in most of the publicly documented or standardized video compression formats can be created with multiple encoders made by different people. Many video codecs use common, standard video compression formats, which makes them compatible. For example, video created with a standard MPEG-4 Part 2 codec such as Xvid can be decoded (played back) using any other standard MPEG-4 Part 2 codec such as FFmpeg MPEG-4 or DivX Pro Codec, because they all use the same video format.

Lossless codecsFFv1: FFv1's compression factor is comparable to Motion JPEG 2000, but based on quicker algorithms (allows real-time capture). Written by Michael Niedermayer and published as part of FFmpeg under to GNU GPL.

Huffyuv: Huffyuv (or HuffYUV) is a very fast, lossless Win32 video codec written by Ben Rudiak-Gould and published under the terms of the GNU GPL as free software, meant to replace uncompressed YCbCr as a video capture format.

Lagarith: A more up-to-date fork of Huffyuv is available as Lagarith.

YULS

x264 has a lossless mode.

MPEG-4 Part 2 codecs

DivX Pro Codec: A proprietary MPEG-4 ASP codec made by DivX, Inc.

Xvid: Free\/open-source implementation of MPEG-4 ASP, originally based on the OpenDivX project.

FFmpeg MPEG-4: Included in the open-source libavcodec codec library, which is used by default for decoding and\/or encoding in many open-source video players, frameworks, editors and encoding tools such as MPlayer, VLC, ffdshow or GStreamer. Compatible with other standard MPEG-4 codecs like Xvid or DivX Pro Codec.

3ivx: A commercial MPEG-4 codec created by 3ivx Technologies.

H.264\/MPEG-4 AVC codecs

x264: A GPL-licensed implementation of the H.264 video standard. x264 is only an encoder.

Nero Digital: Commercial MPEG-4 ASP and AVC codecs developed by Nero AG.

QuickTime H.264: H.264 implementation released by Apple.

DivX Pro Codec: An H.264 decoder and encoder was added in version 7.

Microsoft codecs

WMV (Windows Media Video): Microsoft's family of proprietary video codec designs including WMV 7, WMV 8, and WMV 9. The latest generation of WMV is standardized by SMPTE as the VC-1 standard.

MS MPEG-4v3: A proprietary and not MPEG-4 compliant video codec created by Microsoft. Released as a part of Windows Media Tools 4. A hacked version of Microsoft's MPEG-4v3 codec became known as DivX ;-).

The term audio codec has two meanings depending on the context:

In software, an "audio codec" is a computer program implementing an algorithm that compresses and decompresses digital audio data according to a given audio file format or streaming media audio format. The object of the algorithm is to represent the high-fidelity audio signal with minimum number of bits while retaining the quality. This can effectively reduce the storage space and the bandwidth required for transmission of the stored audio file. Most codecs are implemented as libraries which interface to one or more multimedia players.

In hardware, "audio codec" refers to a single device that encodes analog audio as digital signals and decodes digital back into analog. In other words, it contains both an Analog-to-digital converter (ADC) and Digital-to-analog converter (DAC) running off the same clock. This is used in sound cards that support both audio in and out, for instance.

We mainly talk about audio codec in software aspect.

There are six audio codecs that we often meet: WAV,MP3,WMA,

OGG,APE,ACC.

Then we take three of above for example:WAV,MP3,ACC

WAV: Waveform Audio File Format (WAVE, or more commonly known as WAV due to its filename extension), (also, but rarely, named, Audio for Windows) is a Microsoft and IBM audio file format standard for storing an audio bitstream on PCs. It is an application of the RIFF bitstream format method for storing data in "chunks", and thus is also close to the 8SVX and the AIFF format used on Amiga and Macintosh computers, respectively. It is the main format used on Windows systems for raw and typically uncompressed audio. The usual bitstream encoding is the linear pulse-code modulation (LPCM) format.

MP3: MPEG-1 or MPEG-2 Audio Layer III, more commonly referred to as MP3, is a patented digital audio encoding format using a form of lossy data compression. It is a common audio format for consumer audio storage, as well as a de facto standard of digital audio compression for the transfer and playback of music on digital audio players.

ACC: Advanced Audio Coding (AAC) is a standardized, lossy compression and encoding scheme for digital audio. Designed to be the successor of the MP3 format, AAC generally achieves better sound quality than MP3 at similar bit rates.