Video compression schemes for Web and DVD use make use of a 4:2:0 color sampling pattern, and the DV standard uses 4:1:1 sampling ratios. Refer to the following article for more information about Chroma subsampling.ĭifferent codecs will use different chroma subsampling ratios as appropriate to their compression needs. It is common to represent the ratios of information stored in these different channels in the following way Y:Cb:Cr. The conversion to YCbCr provides two benefits: first, it improves compressibility by providing decorrelation of the color signals and second, it separates the luma signal, which is perceptually much more important, from the chroma signal, which is less perceptually important and which can be represented at lower resolution to achieve more efficient data compression. Because of the design of analog video signals, which represent luma and color information separately, a common first step in image compression in codec design is to represent and store the image in a YCbCr color space.

Video codecs seek to represent a fundamentally analog data set in a digital way. Since commercially available DVDs are usually dual-layer, and hence bigger than the more common single layer writable DVDs, it is often the case that the material has to be compressed again, sacrificing quality so that the media will fit onto a single layer disc. Online video material is encoded in 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.Įncoding media by the public has seen an upsurge with the availability of DVD-writers. There is a complex balance between the video quality, the quantity of the data needed to represent it, also known as the bit rate, the complexity of the encoding and decoding algorithms, robustness to data losses and errors, ease of editing, random access, the state of the art of compression algorithm design, end-to-end delay, and a number of other factors.ĭigital video codecs are found in DVD ( MPEG-2), VCD ( MPEG-1), in emerging satellite and terrestrial broadcast systems, and on the Internet. Engineers and mathematicians have tried a number of solutions for tackling this problem. 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.Īudio and video call for customized methods of compression. Historically, video was stored as an analog signal on magnetic tape.

The compression usually employs lossy data compression. A video codec is a device or software that enables video compression and/or decompression for digital video.

Video codec meaning