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Chapter 10: Compressing: A World of Codecs
We have used the term 'codec' quite a lot in earlier chapters without defining what it means. A codec is just a compression and decompression engine. It does not refer only to digital video, but also to audio and other forms of data. However, in this book, we are only concerned with video and audio codecs.

Previously, we classified codecs as lossless and lossy. This classification is only evident for audio and video codecs. Data compression does not tolerate data losses, so all data codecs are lossless. Imagine compressing a very important archive of documents only to find they are corrupted when you decompress them! You probably do not want that to happen with your video or audio. Lossy video codecs exploit redundancies in the video frames and insensitivities of the human visual system to reduce the amount of data required to represent the original video.

Audio codecs take advantage of properties of the human auditory system, striving to squeeze the bits of the audio stream. Of course, this process is irreversible. By definition, the compressed data cannot be re-constructed to be identical to the source. The aim is to make this process as accurate as possible and thereby produce the best approximation! In technical terms, lossy codecs (given the constraints of bit-rate and distortion) attempt to minimize the error between the original and decompressed streams.

Microsoft Windows has several video and audio codecs installed by default, but most of them are somewhat deprecated and out of date. On the other hand, there are numerous other commercial and free codecs and most are accessible from the Internet. Obviously, people with limited budgets would prefer the free to the commercial ones, and most companies are starting to realize that the end user cannot spend a vast amount of money to encode a video every now and then.

The decoders for the codecs are normally offered free so that anyone can watch a video encoded with a given codec, even if it is commercial.
In this section we present some of the codecs compatible with VirtualDub. There are several others, but their description is out of the scope of this book. We will compare them at the conceptual rather than the implementation level because:

Often, evaluation versions of codecs are offered and if you are keen in keeping up-to-date, you can check the online reviews and community discussions. Always perform your own tests because what might work for someone else might not work for you and vice versa.

• Chapter10: Compressing: A World of Codecs

 
• Interoperability and Open Standards
• Older Codecs
• Adding Codecs
• Compressing Video
  • Saving the Video
  • Job Control
  • Calculating the Video and Audio Bitrate
  • Variable, Average, and Constant Bitrate Modes
  • Multi-Pass Encoding
  • Encoding with DivX
  • Encoding with XviD
  • MPEG-4 in AVI Interoperability
• Compressing the Audio
  • Multiplexing Audio and Video
• Summary

BOOK DETAILS   Paperback, 200 pages Released: May 2005 ISBN: 1904811353 Authors: Georgios Diamantopoulos, John Beuchler, Sohail Salehi

TABLE OF CONTENTS
Introduction
1: Introduction to VirtualDub
2: Video Capture Equipment
3: Capture Preprocessing Free Chapter
4: Processing with VirtualDub
5: Basic Functionality
6: Video Filtering in VirtualDub
7: Professional Video Editing
8: Advanced Topics
9: Frameserving
10: Compressing: A World of Codecs
Index
 

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