Video codec
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A video codec is
The compressed data format usually conforms to a standard video coding format. The compression is typically lossy, meaning that the compressed video lacks some information present in the original video. A consequence of this is that decompressed video has lower quality than the original, uncompressed video because there is insufficient information to accurately reconstruct the original video.
There are complex relationships between the video quality, the amount of data used to represent the video (determined by the bit rate), the complexity of the encoding and decoding algorithms, sensitivity to data losses and errors, ease of editing, random access, and end-to-end delay (latency).
History
Historically, video was stored as an analog signal on
In 1974,
The most popular
The most widely used video coding format, as of 2016, is
AVC has been succeeded by
There are also the open and free VP8, VP9 and AV1 video coding formats, used by YouTube, all of which were developed with involvement from Google.
Applications
Video codecs are used in DVD players, Internet video, video on demand, digital cable, digital terrestrial television, videotelephony and a variety of other applications. In particular, they are widely used in applications that record or transmit video, which may not be feasible with the high data volumes and bandwidths of uncompressed video. For example, they are used in operating theaters to record surgical operations, in IP cameras in security systems, and in remotely operated underwater vehicles and unmanned aerial vehicles. Any video stream or file can be encoded using a wide variety of live video format options. Here are some of the H.264 encoder settings that need to be set when streaming to an HTML5 video player.[12]
Video codec design
Video codecs seek to represent a fundamentally analog data set in a digital format. Because of the design of analog video signals, which represent
It is also worth noting that video codecs can operate in RGB space as well. These codecs tend not to sample the red, green, and blue channels in different ratios, since there is less perceptual motivation for doing so—just the blue channel could be undersampled.
Some amount of spatial and temporal
The output of the transform is first
The decoding process consists of performing, to the extent possible, an inversion of each stage of the encoding process.[15] The one stage that cannot be exactly inverted is the quantization stage. There, a best-effort approximation of inversion is performed. This part of the process is often called inverse quantization or dequantization, although quantization is an inherently non-invertible process.
Video codec designs are usually standardized or eventually become standardized—i.e., specified precisely in a published document. However, only the decoding process need be standardized to enable interoperability. The encoding process is typically not specified at all in a standard, and implementers are free to design their encoder however they want, as long as the video can be decoded in the specified manner. For this reason, the quality of the video produced by decoding the results of different encoders that use the same video codec standard can vary dramatically from one encoder implementation to another.
Commonly used video codecs
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, reducing the need to choose a single dominant video compression format to achieve interoperability.
Standard
Codecs have their qualities and drawbacks. Comparisons are frequently published. The trade-off between compression power, speed, and fidelity (including artifacts) is usually considered the most important figure of technical merit.
Codec packs
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, such as K-Lite Codec Pack, Perian and Combined Community Codec Pack.
See also
- Bit rate
- Comparison of video codecs
- Data compression § Video
- Display resolution
- Frame rate
- List of open-source codecs
- Multiplexing
- Sampling rate
- Subjective video quality
- Transcoding
- Video quality
References
- S2CID 149806273
- ISBN 978-0-12-580203-1
- ^ "T.81 – DIGITAL COMPRESSION AND CODING OF CONTINUOUS-TONE STILL IMAGES – REQUIREMENTS AND GUIDELINES" (PDF). CCITT. September 1992. Retrieved 12 July 2019.
- ^ ISBN 9780852967102.
- ^ a b c d "The History of Video File Formats Infographic — RealPlayer". 22 April 2012.
- ^ "ITU-T Recommendation declared patent(s)". ITU. Retrieved 12 July 2019.
- ^ "MPEG-2 Patent List" (PDF). MPEG LA. Retrieved 7 July 2019.
- ^ "MPEG-4 Visual - Patent List" (PDF). MPEG LA. Retrieved 6 July 2019.
- ^ "AVC/H.264 – Patent List" (PDF). MPEG LA. Retrieved 6 July 2019.
- ^ "HEVC Patent List" (PDF). MPEG LA. Retrieved 6 July 2019.
- ^ "HEVC Advance Patent List". HEVC Advance. Archived from the original on 24 August 2020. Retrieved 6 July 2019.
- ^ "What is the Best Video Codec for Web Streaming? (2021 Update)". Dacast. 2021-06-18. Retrieved 2022-02-11.
- doi:10.17487/rfc6293.
- ^ "Video Codec Design: Developing Image and Video Compression Systems | Wiley". Wiley.com. Retrieved 2022-02-11.
- ^ "Encoding Stage - an overview | ScienceDirect Topics". www.sciencedirect.com. Retrieved 2022-02-11.
External links
- Wyner-Ziv Coding of Video Archived 2011-09-30 at the Wayback Machine describes another algorithm for video compression that performs close to the Slepian–Wolf bound (with links to source code).
- AMD Media Codecs—optional download (formerly called ATI Avivo)