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H.264 and VC-1 are popular video compression standards gaining use in the industry as of 2007. This article outlines commonalities and differences with the two standards. Overview
| H.264 | VC-1 |
|---|
| Goals | Designed to meet a variety of industry needs with many profiles and levels | Designed to require lower processing power. | | Example industry use | Supports studio archiving requirements with 4:4:4 color space;separate black and white (BW) video mode | Supports 4:2:0 compression / color space | | Video Quality | | | | Performance demands | | | | Licensing costs | Similar | Similar | | 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 | March 2006 |
Terminology
All sources for the below information are from the respective specifications listed in the overview section. | H.264 | VC-1 |
|---|
| Partition sizes | 16x16,8x8,4x4 for I-macroblocks, 16x16,16x8,8x16,8x8,8x4,4x8,4x4 for P-macroblocks, 16x16,8x16,16x8,8x8 for B-macroblocks | 8x8 only | | DCT | 4x4, with 8x8 available in High Profile | 8x8, 4x8, 8x4, and 4x4 | | Frame | Used for interlace content. Consists of bottom and top field | Used for progressive or interlaced content | | Macroblock sizes | 16x16 only | 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 |
Features
| H.264 | VC-1 |
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| 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 | | Sub pixel interpolation methods | 6-tap filter for half pixel, averaging for quarter pixels | bicubic and bilinear |
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