Video Compression

<body bgcolor="#FFFFFF" link="#333399" vlink="#555555" alink="#990000"> <table width="90%" border="0" cellspacing="0" cellpadding="0"> <tr valign="top"> <td> <center> <font face="Tahoma, Arial, Helvetica, Geneva, sans-serif" size="2">[Your browser does not support frames! Please download the latest version of <a href="http://www.microsoft.com/ie" target="_blank">Internet Explorer</a> or <a href="http://www.netscape.com/download">Netscape Navigator</a>.]<br> <br> This site has been designed to provide general information on digital video, focusing on the differences between each of its various <a href="formats.html" target="_self">formats</a> and <a href="codecs.html" target="_self">compression</a> schemes. </center> <blockquote> <p><font face="Tahoma, Arial, Helvetica, Geneva, sans-serif" size="2">Digital video is having a significant impact on a variety of industries, from broadcast to multimedia. As commonplace as digital video is, it is often misunderstood and misrepresented. Terms like AVI, Quicktime, and MPEG are thrown around interchangeably without regard to the differences between these formats. While the various forms of digital video look similar to the end user, each format has idiosyncrasies that make it more suitable for some purposes and completely inappropriate for others. <br> <br> To appreciate the differences between digital video formats, you must realize the challenges they try to address. Digital video without audio is captured at about 640 x 480 pixels per frame. Each frame has 307,200 pixels that can be any one of 16.7 million colors. This means that a single frame of video is almost 1 MB. Video is displayed at 30 frames per second. Consequently, without compression, the computer must store, transfer, and display more than 1.5GB for a single minute of video. At these rates, uncompressed digital video is neither practical nor portable without high-end equipment. <br> <br> There are several compression schemes designed to reduce the size of digital video and to reduce the throughput requirements. Compression methods target the same basic areas: frame size, frame rate, image quality, and file storage. Digital video files are compressed for storage and then decompressed for playback. The method of compression and decompression is a CODEC. Various CODECs have been developed to address the many needs of digital video users. </font></p> </blockquote> <font face="Tahoma, Arial, Helvetica, Geneva, sans-serif" size="2">Generally, digital video comes in one of three major formats : <a href="quicktime.html" target="_self">Quicktime</a>, <a href="avi.html" target="_self">AVI</a> and <a href="mpeg.html" target="_self">MPEG</a>. Other formats include Microsoft's up-and-coming <a href="avi.html" target="_self">DirectShow</a>, as well as <a href="streaming.html" target="_self">streaming video</a> formats such as RealVideo and Microsoft's NetShow. Although all of these formats require special players for viewing, the Quicktime and AVI players come pre-installed on most Macintosh and Windows-based machines, respectively. The remaining players can usually be downloaded free from their corresponding web sites. It is important to consider, however, that when displaying video over the internet or distributing video content on CD-ROMs, users must often stop to download and/or install the appropriate player or codec onto their machine in order to view the video, which can become quite an inconvenience. Consequently, most video content intended for computer or internet playback is distributed as either a Quicktime or AVI file, compressed with either the <a href="cinepak.html" target="_self">Cinepak</a> or <a href="indeo.html" target="_self">Indeo</a> codec (pre-installed on most Macs <i>and</i> PCs).</font> </td> </tr> <tr valign="top"> <td> </td> </tr> </table> <p align="right"><br> <br> <font face="Tahoma, Arial, Helvetica, Geneva, sans-serif" size="1">*article excerpt © 1997 Advanstar Communications.<br> all other content © 1998 <a href="http://www.icvinc.com" target="_top">International Corporate Video, Inc</a>.<br> Direct questions/comments to <a href="mailto:alyssai@icvinc.com">alyssai@icvinc.com</a></font></p> <table width="90%" border="0" cellspacing="0" cellpadding="0"> <tr valign="top"> <td> <center> <font face="Tahoma, Arial, Helvetica, Geneva, sans-serif" size="2">[Your browser does not support frames! Please download the latest version of <a href="http://www.microsoft.com/ie" target="_blank">Internet Explorer</a> or <a href="http://www.netscape.com/download">Netscape Navigator</a>.]<br> <br> This site has been designed to provide general information on digital video, focusing on the differences between each of its various <a href="formats.html" target="_self">formats</a> and <a href="codecs.html" target="_self">compression</a> schemes. The following is an excerpt from an article by Tim McElyea (for <a href="http://www.pcgv.com">PC Graphics & Video Magazine</a><font size="1">*</font>) introducing this commonly addressed issue : </font> </center> <blockquote> <p><font face="Tahoma, Arial, Helvetica, Geneva, sans-serif" size="2">Digital video is having a significant impact on a variety of industries, from broadcast to multimedia. As commonplace as digital video is, it is often misunderstood and misrepresented. Terms like AVI, Quicktime, and MPEG are thrown around interchangeably without regard to the differences between these formats. While the various forms of digital video look similar to the end user, each format has idiosyncrasies that make it more suitable for some purposes and completely inappropriate for others. <br> <br> To appreciate the differences between digital video formats, you must realize the challenges they try to address. Digital video without audio is captured at about 640 x 480 pixels per frame. Each frame has 307,200 pixels that can be any one of 16.7 million colors. This means that a single frame of video is almost 1 MB. Video is displayed at 30 frames per second. Consequently, without compression, the computer must store, transfer, and display more than 1.5GB for a single minute of video. At these rates, uncompressed digital video is neither practical nor portable without high-end equipment. <br> <br> There are several compression schemes designed to reduce the size of digital video and to reduce the throughput requirements. Compression methods target the same basic areas: frame size, frame rate, image quality, and file storage. Digital video files are compressed for storage and then decompressed for playback. The method of compression and decompression is a CODEC. Various CODECs have been developed to address the many needs of digital video users. </font></p> </blockquote> <font face="Tahoma, Arial, Helvetica, Geneva, sans-serif" size="2">Generally, digital video comes in one of three major formats : <a href="quicktime.html" target="_self">Quicktime</a>, <a href="avi.html" target="_self">AVI</a> and <a href="mpeg.html" target="_self">MPEG</a>. Other formats include Microsoft's up-and-coming <a href="avi.html" target="_self">DirectShow</a>, as well as <a href="streaming.html" target="_self">streaming video</a> formats such as RealVideo and Microsoft's NetShow. Although all of these formats require special players for viewing, the Quicktime and AVI players come pre-installed on most Macintosh and Windows-based machines, respectively. The remaining players can usually be downloaded free from their corresponding web sites. It is important to consider, however, that when displaying video over the internet or distributing video content on CD-ROMs, users must often stop to download and/or install the appropriate player or codec onto their machine in order to view the video, which can become quite an inconvenience. Consequently, most video content intended for computer or internet playback is distributed as either a Quicktime or AVI file, compressed with either the <a href="cinepak.html" target="_self">Cinepak</a> or <a href="indeo.html" target="_self">Indeo</a> codec (pre-installed on most Macs <i>and</i> PCs).</font> </td> </tr> <tr valign="top"> <td> </td> </tr> </table> <p align="right"><br> <br> <font face="Tahoma, Arial, Helvetica, Geneva, sans-serif" size="1">*article excerpt © 1997 Advanstar Communications.<br> all other content © 1998 <a href="http://www.icvinc.com" target="_top">International Corporate Video, Inc</a>.<br> Direct questions/comments to <a href="mailto:alyssai@icvinc.com">alyssai@icvinc.com</a></font></p> </body>