VC-1 is a video codec specification (SMPTE 421M-2006) implemented by Microsoft as Windows Media Video (WMV) 9, and specified in Blu-ray Disc, and many others. It is designed to achieve state-of-the-art compressed video quality at bit rates ranging from very low to very high with low computational complexity for it to run well on PC platforms. The codec can handle 1920 x 1080 at 6 to 30 Mb/s for high-definition video and is capable of higher resolutions such as 2K for digital cinema, and of a maximum bit rate of 135 Mb/s. An example of very low bit rate video would be 160 x 120 pixel at 10 kb/s.
VC-1 uses some similar transforms to H.261 (1990, the first practical digital coding standard) but much more like H.264/AVC. It includes some distinctive innovations and optimizations. These include 16-bit transforms to help to minimize decoder complexity and interlace coding using data from both fields to predict motion compensation. Also fading compensation improves compression efficiency for fades to/from black and a modified de-blocking filter helps handling areas of high detail.
Individual opinions differ but broadly speaking VC-1 offers at least similar performance and efficiency to H.264/AVC; some say it looks better. VC-1 offers a number of profiles for coding features, and levels of quality combinations defining maximum bit rates. These have a wide range from 176 x 144/15P which may be used for mobile phones, to 2K (2048 x 1536/24P) for movie production.
|Profile||Level||Max Bit Rate||Resolutions and Frame Rate|
|Simple||Low||96Kb/s||176 x 144 @ 15 Hz (QCIF)|
|Medium||384 Kb/s||240 x 176 @ 30 Hz|
|352 x 288 @ 15 Hz (CIF)|
|Main||Low||2 Mb/s||320 x 240 @24 Hz (QVGA)|
|Medium||10 Mb/s||720 x 480 @ 30 Hz (480p)|
|720 x 576 @ 25 Hz (576p)|
|High||20 Mb/s||1920 x 1080 @30 Hz (1080p)|
|Advanced||L0||2 Mb/s||352 x 288 @ 30 Hz (CIF)|
|L1||10 Mb/s||720 x 480 @ 30 Hz (NTSC-SD)|
|720 x 576 @ 25 Hz (PAL-SD)|
|L2||20 Mb/s||720 x 480 @60 Hz (480p)|
|1280 x 720 @ 30 Hz (720p)|
|L3||45 Mb/s||1920 x 1080 @24 Hz (1080p)|
|1920 x 1080 @30 Hz (1080i)|
|1280 x 720 @60 Hz (720p)|
|L4||135 Mbps||1920 x 1080 @60 Hz (1080p)|
|2048 x 1536 @ 24 Hz|
See also: MPEG-4