What is digital video compression?
Compression is the process of removing or restructuring data to reduce file size. When 3DS МАХ writes render to an AVI file, the information in each frame is compressed based on a selection from a list of software controlled encoders / decoders (codecs).
Codecs are divided into three main categories. First of all, they have loss or not. Lossless compression preserves all data in the image, usually using a technique called Run-Length Encoding (RLE). RLE removes continuous areas of the same color by marking the file with a code that restores the duplicate color during decompression. RLE is very efficient for computer-generated graphics with large areas of the same pixels and not very efficient with digitized analog photos and videos, as these images tend to contain few areas of continuous color.
Lossy codecs are designed to recognize and permanently remove information from an image that the viewer is unlikely to see. The algorithm is sensitive to decimation and spreading in the frame rate. Lossy codecs have quality parameters that control the amount of loss (and therefore the size of the file). These codecs are effective for compressing animated ZO geometry combined with analog video.
A second important category of codecs refers to how compression fits into an entire frame, spatially or temporally. Spatial compression examines each frame, recognizes and removes the detail within the frame. Time compression (temporal compression) compares frames over time in order to strategically and gradually remove data. An important type of temporal compression (frame differentiation) remembers only changed pixels of information from successive frames.
Finally, the codecs support specific pixel depths and are platform specific. Some codecs will only compress 8-bit, others support 16-bit and 24-bit compression. Some only play Video for Windows. Decompression (and recompression) occurs when the movie is played. To do this, the View File in 3D Studio MAX mechanism launches MS Windows Media Player (NT or WIN95).
Codecs are essential when animations are played from a CD-ROM drive or hard disk. The codec selected in the output of the 3D Studio MAX render file affects the visual quality and playback speed of digital animation. As shown in Figure 27.3, the codecs are accessed after specifying the output file name with the AVI extension and clicking the Configure button in the File Browsing dialog.
AVI files can be compressed using any of the software codecs that come with Video for Windows. Most likely, you have at least one codec installed with your operating system. Other codecs are installed with multimedia products and Internet browsers. You can also add third-party codecs to your system for a variety of compression formats. To get the results you want for your project, understand how codecs work and experiment a lot.
