VC-1

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VC-1 is the informal name of the SMPTE 421M video codec standard initially developed by Microsoft. WMV3, better known as Windows Media Video 9 codec, served as the basis for development of the VC-1 codec specification. On April 3, 2006, SMPTE announced the formal release of the VC-1 standard as SMPTE 421M. Its most popular implementation is Windows Media Video 9.

1 Format
2 Codec implementations
3 Profiles
4 Bit rates & resolutions
5 References
6 External links

[edit] Format

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. It is widely characterized as an alternative to the latest 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 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 15 companies in the VC-1 patent pool (as of 17 August 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 hold essential patents on the format (since it is a non-exclusive licensing body).^[1]

Both HD DVD and Blu-ray Disc have adopted VC-1 as a mandatory video standard, meaning their video playback devices will be capable of decoding and playing video-content compressed using VC-1. Windows Vista will partially support HD DVD playback by including the VC-1 decoder and related components needed for playback of VC-1 encoded HD DVD movies.^[2]

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 video included with games. By means of an October 31, 2006 update, 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

The FFmpeg project includes a free implementation of this codec.^[3]

[edit] 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 FourCC code.

[edit] WMV3

Simple and Main Profiles of VC-1 remained completely faithful to the existing WMV3 implementation, making WMV3 bitstreams fully VC-1 compliant from the very beginning. 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 YUV 4:2:0 color space, the deprecated interlaced mode was implemented in the less common YUV 4:1:1 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."

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).

[edit] WMVA

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 Player 10 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 DirectShow decoder 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.

[edit] WVC1

WVC1, also known as Windows Media Video 9 Advanced Profile, implements the 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.

[edit] Profiles

	Simple	Main	Advanced
Baseline intra frame compression	Yes	Yes	Yes
Variable-sized transform	Yes	Yes	Yes
16-bit transform	Yes	Yes	Yes
Overlapped transform	Yes	Yes	Yes
4 motion vector per macroblock	Yes	Yes	Yes
¼ pixel luminance motion compensation	Yes	Yes	Yes
¼ pixel chrominance motion compensation	No	Yes	Yes
Start codes	No	Yes	Yes
Extended motion vectors	No	Yes	Yes
Loop filter	No	Yes	Yes
Dynamic resolution change	No	Yes	Yes
Adaptive macroblock quantisation	No	Yes	Yes
B frames	No	Yes	Yes
Intensity compensation	No	Yes	Yes
Range adjustment	No	Yes	Yes
Field and frame coding modes	No	No	Yes
GOP Layer	No	No	Yes
Display metadata	No	No	Yes
	Simple	Main	Advanced

[edit] Bit rates & resolutions

Profile	Level	Maximum Bit Rate	Resolutions by Framerate
Simple	Low	96 kbit/s	176 x 144 / 15 (QCIF)
Simple	Medium	384 kbit/s	240 x 176 / 30 352 x 288 / 15 (CIF)
Main	Low	2 Mbit/s	320 x 240 / 24 (QVGA)
	Medium	10 Mbit/s	720 x 480 / 30 (480p) 720 x 576 / 25 (576p)
	High	20 Mbit/s	1920 x 1080 / 30 (1080p)
Advanced	L0	2 Mbit/s	352 x 288 / 30 (CIF)
	L1	10 Mbit/s	720 x 480 / 30 (NTSC-SD) 720 x 576 / 25 (PAL-SD)
	L2	20 Mbit/s	720 x 480 / 60 (480p) 1280 x 720 / 30 (720p)
	L3	45 Mbit/s	1920 x 1080 / 24 (1080p) 1920 x 1080 / 30 (1080i) 1280 x 720 / 60 (720p)
	L4	135 Mbit/s	1920 x 1080 / 60 (1080p) 2048 x 1536 / 24