Global Motion Compensation(synonyms: GMC)Global Motion Compensation, or GMC, is a technique used in MPEG-4 encoding that allows greater compression for scenes with camera pans and other motion that affects the entire video frame simultaneously. By contrast, older formats like MPEG-2 always use separate calculations for each 16x16 pixel block in the frame, requiring more bits.
Due to the increased complexity of GMC over standard block based motion estimation, hardware MPEG-4 encoders often don't support it, making it risky to use for encoding in many situations. There are also differences in how its implemented in different MPEG-4 codecs, with DivX using a much simpler version than XviD. GMC complexity can be determined by the number of warp points supported. DivX uses a single warp point, while XviD can use up to three. Most hardware that supports GMC is only capable of rendering video with 1 warp point.
Related guides:
How to play MP4 files
How to play AVI
Convert DVD to XviD with meGUI
Related software tools:
3ivX D4 (BeOS) v4.5 (Freeware)
3ivX is an excellent video quality MPEG-4 codec for BeOS.
3ivX Delta Codec (Amiga 68k) v1.0d3 (Freeware)
3ivX is an MPEG4 codec based on the MPEG4v3 ISO standard.
3ivx MPEG-4 v5.02 (Commercial demo)
3ivX is an excellent quality video codec based on the MPEG-4 video standard.
3ivx MPEG-4 For Mac OS X v5.02 (Commercial demo)
3ivX is an MPEG-4 codec that allows playback of all MPEG-4 compliant formats, such as DivX, 3ivX and XviD.
AviSynth v2.5.8 RC4 [080831] (Open source)
AviSynth is an extremely powerful frameserver for Windows that allows using VirtualDub and TMPGEnc plugins as well as tons of its own plugins to be added to the frameserving process.
DivX v6.8.4 (Freeware)
The latest version of the DivX. That is, you need to have this file installed if you want to watch DivX movies. And latest codec gives you the best quality.
DivX (Win98/ME) v5.2.1 (Shareware)
The latest version of the DivX codec for Win98/ME platforms. You need to have this codec installed in case you want to watch or encode DivX movies.
DivX ;-) MPEG4 Codec release 3.11 alpha (Freeware)
DivX ;-) is a hacked MPEG4 codec that allows you to watch and encode DivX ;-) video clips. You really need this one, trust me...
DivX Create v6.3 (Shareware)
This is the DivX pack you want if you're planning to encode DivX movies on your own.
DivX for Linux v5.05 (Freeware)
Official DivX5 codec for Linux -- provides same features and same quality as the Windows version does.
DivX for Mac OS X v6.7 (Shareware)
DivX5 for Mac is _the_ official DivX codec for Mac -- it has been developed by DivX Networks, same guys who have developed DivX4 for Win. Excellent MPEG-4 based video codec.
DivX Pro (Win98/ME) v5.2.1 (Shareware)
DivX is an extremely popular implementation of the MPEG-4 standard.
DivX Pro for Mac OS (15 day trial) v5.1.1 (Freeware)
DivX5 for Mac is _the_ official DivX codec for Mac -- it has been developed by DivX Networks, same guys who have developed DivX4 for Win. Excellent MPEG-4 based video codec.
XviD Bitrate Calculator v1.20 (Freeware)
Nice little bitrate and resolution calculator for XviD videos, which does everything you can ask from a bitrate calculator. Only nag is the installation of the tool, which can get painful.
XviD Codec v1.1.3 (Koepi's 28.06.2007 Final Build) (Open source)
XviD is an open source video codec that lets you play and create MPEG-4 compatible videos.
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