VC-1
From DigiWiki
VC-1 is a video compression technology from Microsoft, based on their WMV technology.
Contents |
[edit] Format
VC-1 is primarily designed for HD video, and is similar in terms of compression ratio to H.264. VC-1 is the most commonly used format for HD DVD movies, with Blu-ray movies also starting to use this format. VC-1 should not be confused with WMVHD/WMV-HD which is the earlier Windows Media standard for High Definition (found as a file on pre-revolution DVD discs. VC-1 uses high bitrates at the intended resolution converse to WMVHD/WMV-HD which use much higher resolution at lower bitrates with instruction sets built into players to allow the downsizing (scaling) of the video to correct playback resolution.
[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 and resolutions
| Profile | Level | Maximum Bit Rate | Resolutions by Framerate |
|---|---|---|---|
| Simple | Low | 96 kbit/s | 176 x 144 / 15 (QCIF) |
| 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 |
[edit] Overview
| H.264 | VC-1 | |
|---|---|---|
| Goals | Designed to meet a variety of industry needs with many profiles and levels <ref>http://www.itu.int/rec/dologin_pub.asp?lang=e&id=T-REC-H.264-200503-I!!PDF-E&type=items Section 0.3</ref> | Designed to require lower processing power. [1] |
| Example industry use | Supports studio archiving requirements with 4:4:4 color space; separate black and white (BW) video mode | Supports 420 compression / color space<ref>SMPTE Draft Standard for Television, SMPTE421M, SMPTE Technology Committee C24 on Video Compression Technology, Proposed SMPTE Standard for Television: VC-1 Compressed Video Bitstream Format and Decoding Process, Date: 2005-08-23,
Copyright 2003-2005 THE SOCIETY OF MOTION PICTURE AND TELEVISION ENGINEERS 595 W. Hartsdale Ave. White Plains, NY 10607 E-mail eng@smpte.org Web www.smpte.org </ref> |
| Video Quality | Judged better for low bit rate single pass encoding<ref>
MSU Subjective Comparison of Modern Video Codecs.
| Judged better for high bit rate encoding<ref>German C’T Magazine, May 03, compared various codecs, including VC-1 and H.264, and selected VC-1 as producing the best subjective and objective quality for high-definition (HD) video. [2] intro [3] [4] [5]</ref> <ref> http://www.microsoft.com/windows/windowsmedia/howto/articles/vc1techoverview.aspx#QualityComparison </ref> |
| Performance demands | Can decode 1080p video on more PCs [6] [7] [8] | |
| Licensing costs | Similar [9] | Similar [10] [11] |
| Documentation | 41 figures in the spec | 186 figures in the spec. Reference encoder and decoder come with external documentation. |
| Timeline: First version of specification published | May 2003<ref>From H.264 article intro</ref> | March 2006 [12] |
[edit] Terminology
All sources for the below information are from the respective specifications listed in the overview section.
| H.264 | VC-1 | |
|---|---|---|
| Block | MxN size | An 8x8 array of samples |
| Frame | Used for interlace content. Consists of bottom and top field | Used for progressive or interlaced content |
| Macroblock | 16x16 array of samples | Same |
| Motion vector | Two dimensional vector offset from current position to reference frame | Same |
| Picture | A field or frame | Same |
| Skipped macroblock | No data is encoded for macroblock | Same |
[edit] Features
| H.264 | VC-1 | |
|---|---|---|
| Bitstream formats | NAL and byte stream | single bit stream |
| Bitstream format | Sequence header (SPS, sequence parameter set), picture header (PPS, picture parameters set), slice, macroblock | Same, called Seq_layer, and Pic_layer |
| CABAC | Yes | No |
| CAVLC | Yes | No |
| Variable Length Coding | Yes | Yes |
| Slice | Can be non contiguous in picture | Must be contiguous |
| B slice used for predicting other pictures | Yes | No<ref>Defined in section 4.12, Definition of terminology of VC-1 specification.</ref> |
| Sub pixel interpolation methods | 6-tap filter for half pixel, averaging for quarter pixels | bicubic and bilinear |
- tables borrowed from open-licensed source.
