Windows Media Video 9

 

Windows Media Video 9 is the Microsoft implementation of the VC-1 SMPTE standard. It supports Simple, Main, and Advanced profiles. It uses the FOURCC code WMV3.

VC-1 is a video codec specification that has been standardized by the Society of Motion Picture and Television Engineers (SMPTE) and implemented by Microsoft as Microsoft Windows Media Video (WMV) 9. This specification was proposed by Microsoft and is based on the technology developed for the Windows Media Video 9 codecs. The VC-1 standard is published in SMPTE 421M-2006, VC-1 Compressed Video Bitstream Format and Decoding Process. VC-1 has three complexity profiles: simple, main, and advanced. Higher profiles offer more features and more efficient encoding tools, but also increase the required processing power on both the encoding and decoding side.

 

For more details about VC-1 go here

 

( Courtesy: Wiki WMV9 )

 

Windows Media Video (WMV) is the most recognized codec within the WMV family. Usage of the term WMV often refers to this codec only. Its main competitors are MPEG-4 AVC, RealVideo, DivX, and Xvid.

 

The first version of the codec, WMV 7, was introduced in 1999, and was built upon Microsoft's implementation of MPEG-4 Part 2. Continued proprietary development led to newer versions of the codec, but the bit stream syntax was not frozen until WMV 9. While all versions of WMV support variable bit rate, average bit rate, and constant bit rate, WMV 9 introduced several important features including native support for interlaced video, non-square pixels, and frame interpolation. WMV 9 also introduced a new profile titled Windows Media Video 9 Professional, which is activated automatically whenever the video resolution and bit rate exceed 300,000 pixels (eg., 512 × 586) and 1000 kbit/s (eg., 1001 kbit/s). It is targeted towards high-definition video content, at resolutions such as 720p and 1080p.

The Simple and Main profile levels in WMV 9 are compliant with the same profile levels in the VC-1 specification. The Advanced Profile in VC-1 is implemented in a new WMV codec called Windows Media Video 9 Advanced Profile. It improves compressions efficiency for interlaced content and is made transport-independent, making it able to be encapsulated in an MPEG transport stream or RTP packet format. The codec is not compatible with previous WMV 9 codecs, however.

WMV is a mandatory video codec for PlaysForSure-certified online stores and devices, as well as Portable Media Center devices. The Microsoft Zune, Xbox 360, Windows Mobile-powered devices with Windows Media Player, as well as many uncertified devices, support the codec. WMV HD mandates the use of WMV 9 for its certification program, at quality levels specified by Microsoft.[14] WMV is also the only supported video codec for the Microsoft Silverlight platform.

 

Simple and Main Profiles

( Courtesy: Microsoft )

 

The Windows Media Video 9 Simple and Main profiles fully conform to the SMPTE VC-1 standard and provide high-quality video for streaming and downloading. These profiles support 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.

 

Advanced Profile

( Courtesy: Microsoft )

 

The Windows Media Video 9 Advanced profile fully conforms to the SMPTE VC-1 standard, supports interlaced content, and is transport-independent. Content creators can use this profile to deliver either progressive or interlaced content at data rates as low as one-third that of the MPEG-2 codec—with the same quality as MPEG-2.

In the past, interlaced video content was always de-interlaced before encoding with the Windows Media Video codec. Now, encoding applications such as Windows Media 9 Series, and third-party encoding solutions can support compression of interlaced content without first converting it to progressive content. Maintaining interlacing in an encoded file is important if the content is ever rendered on an interlaced display, such as a television.

Transport independence also enables the delivery of Windows Media Video 9 Advanced Profile over systems that are not Windows Media-based, such as standards-based broadcast infrastructures (through native MPEG-2 transport streams), wireless infrastructures (using real-time transfer protocol [RTP]), or even DVDs.

 

Comparison of WMV 9 Advanced Profile

( Courtesy: Microsoft )

 

The following table compares Windows Media Video 9 Advanced Profile to competing compression technology.

Video Data	Industry Compression	Windows Media*	Compression Savings
480/24p 720x480 pixels/frame x 8 bits per channel x 24 fps	MPEG-2 at 4–6 Mbps	Windows Media Video 9 Advanced Profile at 1.3–2 Mbps	3:1
480/30i 720x480 pixels/frame x 8 bits per channel x 30 fps	MPEG-2 at 6–8 Mbps	Windows Media Video 9 Advanced Profile at 2–4 Mbps	2–3:1
720/24p 1280x720 pixels/frame x 8 bits per channel x 24 fps	MPEG-2 at 19 Mbps	Windows Media Video 9 Advanced Profile at 5–8 Mbps	2.4–3.8:1

 

*Content dependent

 

WMV9 Screen & Image

( Courtesy: Microsoft )

 

Windows Media Video 9 Screen

The Windows Media Video 9 Screen codec is optimized for compressing sequential screenshots and highly static video that is captured from the computer display, which makes it ideal for delivering demos or demonstrating computer use for training. The codec takes advantage of the typical image simplicity and relative lack of motion to achieve a very high compression ratio.

During the encoding process, the codec automatically switches between lossy and lossless encoding modes, depending on the complexity of the video data. For complex data, the lossless mode preserves an exact copy of the data. For less complex data, the lossy mode discards some data to achieve a higher compression ratio. By automatically switching between these two modes, the codec maintains video quality while maximizing compression.

Overall, the Windows Media Video 9 Screen codec delivers better handling of bitmap images and screen motion, even on relatively modest CPUs. It is also up to 100 times more efficient than the commonly-used run length encoding.

 

Windows Media Video 9 Image Version 2

The Windows Media Video 9 Image Version 2 codec is different from the other video codecs. Instead of processing uncompressed video, it transforms still images into video by using pan, zoom, and cross-fade transitions between clips to create an unlimited number of effects.

The results can then be delivered at data rates as low as 20 kilobits per second (Kbps). These files are compressed using either constant bit rate (CBR) or one-pass variable bit rate (VBR) modes.

 Note   The Windows Media Video 9 Image Version 2 codec is not compatible with the Windows Media Video 9 Image codec.

 

 

WMV Container Format

( Courtesy: Wiki WMV9 )

 

A WMV file is in most circumstances encapsulated in the Advanced Systems Format (ASF) container format. The file extension .WMV typically describes ASF files that use Windows Media Video codecs. The audio codec used in conjunction with Windows Media Video is typically some version of Windows Media Audio, or in rarer cases, the deprecated Sipro ACELP.net audio codec. Microsoft recommends that ASF files containing non-Windows Media codecs use the generic .ASF file extension.Although WMV is generally packed into the ASF container format, it can also be put into the AVI or Matroska container format. The resulting files claim the .AVI, or .MKV file extensions, respectively. WMV can be stored in an AVI file when using the WMV 9 Video Compression Manager (VCM) codec implementation. Another common way to store WMV in an AVI file is to use the VirtualDub encoder.This container can optionally support digital rights management using a combination of elliptic curve cryptography key exchange, DES block cipher, a custom block cipher, RC4 stream cipher and the SHA-1 hashing function.