MacHouse

   Last updated: February 19, 2011

This section is a knowledge database concerning video compression.

Video compression...  What is it?  Literally speaking, video compression is a way of making video files smaller.  More specically, video compression is a method by which the pixels that aren't easily observable to human eyes are ignored or assimilated into adjacent ones.  Video decompression or decoding is a method by which original pixels are recovered to the orignal or near-original state.  Lossy compression refers to the data reduction by which a decoded video cannot be recovered to the original state.  In contrast, lossless compression refers to the data reduction by which a decoded video can be recovered to the original state. 

There are a number of video compressors.  Some of the video compressors that are available for the Mac OS include Animation, 3ivx, DivX, Xvid, MPEG-1, MPEG-2, MPEG-4 Part II, H.264 and DV.  There are other video compressors like On2 VP6, On2 VP7 and Sorenson Spark.  This group of video compressors only applies to Flash videos (.FLV).  In other words, video files that are compressed with any of the video compressors in the first group can be opened with QuickTime Player.  And other video files that are compressed with any of the video compressors in the second group cannot be read by QuickTime and can only be accessible with Adobe's Flash.  There is another group of video compressors that QuickTime cannot directly decode.  The Windows Media Video (WMV) format supports different video compressors such as Microsoft MPEG-4 Video Codec V1, V2, V3, Windows Media Video V7 (WMV1), Windows Media Screen V7 (MSS1), Windows Media Video V8 (WMV2), Windows Mdia Video 9 (WMV3), Windows Media Video 9 Screen (MSS2)...*  Apple's QuickTime Player cannot directly decode videos that are compressed with any of these WMV compressors.  Nonetheless, a free QuickTime plug-in by Flip4Mac allows QuickTime users to decode WMV-compressed videos for Mac.

QuickTime plug-ins?  More precisely, they are called QuickTime components.  These compression scripts are stored inside Library > QuickTime.  If you want to compress a video file, for instance, with 3ivx, you must have a specific QuickTime component that is written for 3ivx.  Furthermore, if you want to decode (play back) a video file that is compressed, say, DivX 6, you must have a QuickTime component that is written to decode such compression, not for any DivX version but particularly for DivX 6.