In The Rise of Flash Video - Tom Green tells us:
This is not to say QuickTime and Windows Media are dead technologies. They aren’t by a long shot, but when it comes to putting video on the web, the Flash Player has rapidly become the only game in town.Why has this happened?
Market PenetrationThe Flash player is installed on a higher percentage of end user computers than any other video format. Although not all end users have the latest version installed (so they may not support the latest Flash video codec), Flash still enjoys the best overall support. And as more consumer sites continue to move to the Flash video format, it's even more likely that your audience will have an appropriate player.
In some organizations, you have desktops that are guaranteed to have a particular player installed. So this may be less of an issue. Check with your IT department to find out what you have installed. Note: there are organizations that intentionally remove particular media players, even Flash.
Consistent PlaybackThe Flash video format works well across PCs, Macs, Linux, etc. Flash files are very consistent in their playback. They also handle variable connection speeds pretty well. It's nice to know that it will play well across varied platforms.
Theoretically, the other formats can work across different platforms, e.g., there's a Windows Media Player for Mac OS X and some ways to playback WMV Format on Linux. The reality is that the Flash video format will work much more consistently across different platforms.
Better "Streaming"In general, the Flash video format is very good at playing as it streams down additional content. WMV Format, Quicktime and Real either require a streaming server to achieve the effect or do not do as good of a job. While they've improved, it still seams like these other technologies are behind in progressive download.
Advanced FeaturesThe Flash video format provides some very nice features for overlays and interactivity.
Quality DebateThere is quite a bit of debate on the web about the quality of the resulting video and also about the relative bandwidth required for the video. Several sources say that the same quality flash video format movie will have a larger file size and require greater bandwidth. It's not clear how true this is. And it also changes as codecs emerge. For most eLearning applications, this has not been enough to differentiate the choices.
ProtectionOne of the specific questions I was asked was around caching and protection of the movie. Unfortunately, the Flash Video Format sent via progressive download end up in the user's cache and are unprotected. From Adobe:
Flash video content and MP3s delivered to Flash Player using a normal web server are delivered through progressive download. This content is cached on the end user's hard drive and can be easily accessed—and possibly stolen by the user. By contrast, audio, video, and data streamed to Flash clients using Flash Media Server are not cached on local client machines.The only way around this is to use a Flash Media Server. Of course, the same is true of the other formats. Delivering a file via a standard HTTP request (without a streaming server) will leave the asset available.