Practical DV FilmMaking

is not much movement but lighter compression to where you need more detail on screen, perhaps during an action sequence. This process avoids 'data spikes', where sudden increases in data cause a movie to stop playing on the user's PC because too much data is needed.

RealG2 - good for web work, not for other uses

This codec is widely used on the web. It uses 'temporal scaleability', which means that the result for the user is smoother than others even on a wide range of computers or devices. This means movies encoded with it play at a high frame rate for fast processors and low for slow ones. This codec is hard to beat in terms of the number of users who may have access to it on the web and the ease with which the rest can download it (for free).

Sorenson - good all-rounder

This is a really good, high-quality codec and looks better than most at a screen size of 320 X 240. It's a good solution for movies that are going to be viewed over broadband connections, but some editions (notably the Developer Edition) cater for the other users by enabling scaleable streaming. One aspect which puts many people off using this codec is the length of time it takes to encode a movie in this way, but it remains the method of choice for most short movies, for the web and CD.

Intel Indeo 4 and 5 - good, but mainly for high power

With this method of compression you get a good result with high picture quality, but it is only viable for high-powered PCs or Macs. Version 5 allows for progressive downloads. Intel's codec is generally better than Cinepak, but cannot match the picture quality of the Sorenson.

Formats

There are various ways of decoding the information once it has been coded for sending over the Internet. Computer manufacturers have adopted different formats for codecs.

Video for Windows - short films and CD-ROM

This kind of file will have an '.avi' suffix at the end. The advantage of this one is that it comes as stand­ard with Windows operating systems. This format is primarily aimed at the CD-ROM movie, for short films stored and viewed on disc. Reliability is an issue here, as this format is notorious for putting audio and vision out of sync. The preferred codec for this format is Cinepak, which has widespread use but is poor in picture quality, but for better quality it can use Intel's Indeo system, version 4 or 5.

Microsoft Windows Media - good streaming tool, flexible

This kind of file has an '.ask' after it and is designed to cope with almost any user, from the snail's pace 14