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Tech Review #4 |
Video! Optimizing Video for the Web
The next logical step in delivering graphics over the Web is to deliver animiated graphics and/or video. The main challenge with video is the file size and bandwidth requirements which can potenially equate to hundreds of megabytes as well as lengthy delivery times. Video poses an even greater problem than graphics with regards to bandwidth and performance. Once again a motivation is created to reduce or compress the size of the file while not denegrating the quality of the picture. The topic of video optimization is extremely broad and complex, but the following will provide a thirty-thousand foot high view.
The most common formats used for delivery over the Web are the following: AVI, MOV, MPG. A new form of video delivery, ASF or Advanced Streaming Format, is also becoming popular over the Web. ASF is currently a much better method than any of its predacessors.
AVI ... AVI stands for Audio Video Interleave and was developed by Microsoft. It is the most common video format for the PC, but it does not offer the compression advantage the MPEG has. AVI is equivalent to the bitmap for graphics. It is the video file format without optimization and is the starting point for further compression methods.
MOV ... MOV is the PC file extension used for QuickTime "movies". QuickTime is an Apple product which is very popular with games. This is old technology and is not a preferred method for Web delivery, but it is still used sometimes.
MPEG ... MPEG stands for Moving Picture Experts Group (a working group of ISO) and uses a file extension of MPG. MPG is pronounced M-PEG. MPG is a family of standard compression formats which were developed by the Picture Expers Group. It is popular because of the reduced size of the compressed video as well as the fact that the quality is better than some of the other choices. To view the MPG format a user must have the proper hardware and software. Like its graphic counterpart, JPEG, MPEG uses lossy compression to optimize moving images. There are two types of MPEG files, MPEG-1 and -2. MPEG-1 offers resolution of 352-by-240 at 30 fps (frames per second). MPEG-2 is newer and offers resolutions of 720x480 and 1280x720 at 60 fps, with full CD-quality audio. MPEG-2 is what is used with the new DVD technology and is capable of compressing a 2 hour movie into a few gigabytes. The next generation of MPEG will be MPEG-4 and will be based on the QuickTime file format.
ASF ... ASF is exciting technology for anyone involved with the Web. ASF stands for Advanced Streaming Format and was developed by Microsoft. A new tool suite called NetShow is available from Microsoft to convert AVI files to ASF files, but ASF offers a higher compression rate than AVI files. ASF is a set of rules for describing how multimedia data is organized and laid out on disk. These rules are optimized for streaming the data over a network, and for playing back the data at the client end. The data stored in the ASF format can represent dynamic, advanced multimedia presentations. What makes ASF files so unique and so preferable is that while other methods require that the entire file be transferred to a user's PC, ASF sends enough to get you started, so you don't have to wait for everything. This is accomplished because ASF files are made up of a collection of data objects which share basic characteristics. These shared characteristics are three fields: (1) a 16-byte-long field containing a GUID; (2) an 8-byte-long field containing the size of the object; and (3) a field as long as the second field (minus 24 bytes) containing data of some kind or other. GUIDs are unique identifiers of objects.
Together with AVI, older multimedia technologies such as MPEG-1, MPEG-2, and QuickTime have set the stage for the digital multimedia revolution. Through them, digital multimedia has become a reality. However, like AVI, these older technologies were not originally developed with Internet delivery and Web presentation in mind; hence, it is natural that MPEG-1, MPEG-2, and QuickTime are less than optimal than ASF for streaming synchronized multimedia presentations in the new internet environment.
Hyperlinks for Further Research:
MPEG Pointers and Resources:
http://www.mpeg.org/MPEG/
Resource for information on MPEG covering FAQs, industry news, audio and video players, systems, companies, products, and shareware
Video on theWorld Wide Web:
http://www.videonics.com/videos/about-web-video.html
Discusses on-the-fly video delivery and the necessary compromises. Includes links to more information about MPEG and the advantages and disadvantes of streaming video.
About ASF:
http://www.microsoft.com/asf/aboutASF.htm.
Contains an overview of ASF and answers to common questions.
The Audio & Video Compression Page:
http://www.fedele.com/website/compress/compress.htm.
Good collection of links to technical MPEG and JPEG FAQs, as well as audio and video compression information and an introduction to wavelets
AVI Overview:
http://www.rahul.net/jfm/avi.html
Excellent overview of Video for Windows, ActiveMovie, and AVI written by John F. McGowan. Includes information on utilities, system administration and authoring, as well as installation, configuration, programming information, and technical topics.
Page last updated on 05/30/2000.