Video codec

A video codec is an electronic circuit or software that compresses or decompresses digital video. It converts raw (uncompressed) digital video to a compressed format or vice-versa. In the context of video compression, "codec" is a concatenation of "encoder" and "decoder"—a device that only compresses is typically called an encoder, and one that only decompresses is a decoder.

The compressed data format usually conforms to a standard video compression specification. 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).

VC-1

SMPTE 421M, informally known as VC-1, is a video coding format. It was initially developed as the proprietary video format Windows Media Video 9 by Microsoft in 2003 and officially approved as a SMPTE video codec standard on April 3, 2006.

It is today a supported standard found in Blu-ray Discs, Microsoft's Silverlight framework, and the now-discontinued HD DVD.

Format

VC-1 is an evolution of the conventional DCT-based video codec design also found in H.261, MPEG-1 Part 2, H.262/MPEG-2 Part 2, H.263, and MPEG-4 Part 2. It is widely characterized as an alternative to the ITU-T and MPEG video codec standard known as H.264/MPEG-4 AVC. VC-1 contains coding tools for interlaced video sequences as well as progressive encoding. The main goal of VC-1 Advanced Profile development and standardization was to support the compression of interlaced content without first converting it to progressive, making it more attractive to broadcast and video industry professionals.

Both HD DVD and Blu-ray Disc have adopted VC-1 as a video standard, meaning their video playback devices will be capable of decoding and playing video-content compressed using VC-1. Windows Vista partially supports HD DVD playback by including the VC-1 decoder and some related components needed for playback of VC-1 encoded HD DVD movies.