VC-1 is the informal name of the
SMPTE421M video codecstandard initially developed by Microsoft. It was released on April 3, 2006by SMPTE. It is now a supported standard for HD DVDs, Blu-ray Discs, and Windows Media Video9.
VC-1 is an evolution of the conventional DCT-based video codec design also found in
H.261, H.263, MPEG-1, MPEG-2, and MPEG-4 Part 2. It is widely characterized as an alternative to the latest ITU-Tand MPEGvideo 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 development and standardization is to support the compression of interlaced content without first converting it to progressive, making it more attractive to broadcast and video industry professionals.
Although widely considered to be Microsoft’s product, there are actually fifteen companies in the VC-1 patent pool (as of
August 17 2006). As an SMPTE standard, VC-1 is open to implementation by anyone, although implementers are hypothetically required to pay licensing fees to the MPEG LA, LLC licensing body or directly to its members, who claim to hold essential patents on the format (since it is a non-exclusive licensing body). [Cite web | url = http://www.mpegla.com/news/n_06-08-17_pr.pdf | title = MPEG LA, LLC. Press Release| accessmonthday = August 17 | accessyear = 2006]
HD DVDand Blu-ray Dischave 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 Vistapartially supports HD DVD playback by including the VC-1 decoder and some related components needed for playback of VC-1 encoded HD DVD movies.Cite web | year = 2006 | url = http://www.microsoft.com/windows/windowsmedia/howto/articles/vc1techoverview.aspx | title = VC-1 Technical Overview | publisher = Microsoft Corporation | accessmonthday = October 5 | accessyear = 2006]
Microsoft has designated VC-1 as the
Xbox 360 video game console’s official video codec, and game developers may use VC-1 for full motion videoincluded with games. By means of an October 31, 2006update, people can now play all formats of Windows Media Video on the Xbox 360 from a disc, USB storage device, or streaming from their PC via Windows Media Connect/Windows Media Player 11. This allows anyone to play VC-1 encoded files on the console.
FFmpegproject includes a free VC-1 decoder. [cite web|url=http://code.google.com/soc/2006/ffmpeg/appinfo.html?csaid=5AA777DB19E2BB24|title=VC-1 - Google Summer of Code|accessdate=2007-03-21]
Microsoft codec implementations
The VC-1 codec specification has so far been implemented by Microsoft in the form of 3 codecs, each identified with a unique
Simple and Main Profiles of VC-1 remained completely faithful to the existing WMV3 implementation, making WMV3 bitstreams fully VC-1 compliant.The WMV3 codec was designed to primarily support progressive encoding for computer displays. An interlaced encoding mode was implemented, but quickly became deprecated when Microsoft started implementing WMV Advanced Profile. Whereas WMV3 progressive encoding was implemented in the color space, the deprecated interlaced mode was implemented in the less common color space.
The Windows Media Video 9 (WMV3) codec implements the Simple and Main modes of the VC-1 codec standard, providing high-quality video for streaming and downloading. "It provides support for a wide range of bit rates, from high-definition content at one-half to one-third the bit rate of MPEG-2, to low-bit-rate Internet video delivered over a dial-up modem. This codec also supports professional-quality downloadable video with two-pass and variable bit rate (VBR) encoding. Windows Media Video 9 is already supported by a wide variety of players and devices." Fact|date=July 2007
A number of high definition movies and videos have been released commercially in a format dubbed
WMV HD. These titles are encoded with WMV3 Main Profile @ High Level (MP@HL).
WMVA was the original implementation of WMV Advanced Profile prior to the acceptance of the VC-1 draft by SMPTE. The codec was distributed with
Windows Media Player10 and Windows Media Format SDK 9.5 install packages. There are slight bitstream differences between WMVA and WVC1, so consequently WMVA is handled by a different DirectShowdecoder than WVC1. Some 3rd party hardware and software decoders only decode WMVA based content. As of 2006, WMVA is considered a deprecated codec because it is not fully VC-1 compliant.
WVC1, also known as Windows Media Video 9 Advanced Profile, implements a more recent and fully compliant Advanced Profile of the VC-1 codec standard. It offers support for interlaced content and is transport independent. With the previous version of the Windows Media Video 9 Series codec, users could deliver progressive content at data rates as low as one-third that of the MPEG-2 codec and still get equivalent or comparable quality to MPEG-2. The Windows Media Video 9 Advanced Profile codec also offers this same improvement in encoding efficiency with interlaced contents. A decoder for WVC1 is included in Windows Media Player 11, which is bundled with Windows Vista and is available as a download for Windows XP.
Bit rates and resolutions
Due to its origins in Microsoft's WMV9 codec, the most popular implementations of VC-1 encoders have so far been done by Microsoft, though third-party implementations exist as well. Sonic Cinevision PSE, a professional VC-1 encoding tool used predominantly in
HD DVDand Blu-rayencoding, is a commercial version of Microsoft's PEP (Parallel Encoder) encoding tool and VC-1 Analyzer tool. Microsoft owns the code development whereas Sonic Solutionsowns the sales and distribution. Microsoft also provides a separate VC-1 Encoder SDK which allows any company or software developer to integrate VC-1 encoding into their applications.Non-Microsoft VC-1 implementations (based entirely on the SMPTE specifications) have been done by Tandberg Televisionand MainConcept.
Windows Media Encoder9 Series encodes VC-1 compliant video files, including WVC1 FourCCmedia. Windows Media Format 11 Runtime or Windows Media Player 11 must be installed on the computer to ensure full VC-1 compliance across all three profiles (Simple, Main and Advanced). If either of these are installed, Windows Movie Makercan also save VC-1 compliant videos, as can any other application built on the Windows Media Format SDK or Windows Media Codec DMOs. A Windows Media Encoder Studio Edition was initially announced for professional encoding but later cancelled by Microsoft. Microsoft Expression Encoderwhich is part of Expression Mediaand Expression Studio is aimed at encoding VC-1 (WMV9) video for Silverlightstreaming experiences.
Comparison of H.264 and VC-1
*cite web | title=VC-1 Profiles and Levels | work=VC-1 | url=http://www.microsoft.com/windows/windowsmedia/forpros/events/NAB2005/VC-1.aspx#VC1_Profiles_and_Levels | accessmonthday=December 12 | accessyear=2005
*cite web | title=Microsoft WMV Codec Implementations | work=VC-1 | url=http://www.microsoft.com/windows/windowsmedia/9series/codecs/video.aspx | accessmonthday=February 28 | accessyear=2006
* [http://wiki.multimedia.cx/index.php?title=Understanding_VC-1 VC-1 reference software analysis] at the MultimediaWiki
*RFC 4425 – IETF RTP Payload Format for Video Codec 1
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