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Progressive Download (FLV)
Macromedia Flash MX 2004 and Flash Player 7 introduced a new technique called progressive download for delivering video in Flash. This method enables developers to use ActionScript commands to feed external FLV files into a Flash movie and play them back during runtime.
In this method, the video content (FLV file) is kept external to the other Flash content and the video-playback controls (the video player) in the SWF file.
When the video is played, the video file is downloaded to the client's computer (hard drive) before playback. The file is served from a normal web server through an HTTP request just like a normal web page or any other downloadable document.
Unlike traditional download-and-play methods of video delivery, however, the file starts playing before it has completely downloaded when you use progressive download.
Pros and Cons
Keeping the video external and separate to the SWF file offers a number of benefits over embedded video, including the following:
Easy to update: It's relatively easy to add or change content independently of the video player and without the need to republish the SWF file.
Small SWF file size: Your SWF file can remain very small for fast page loads and the video can be delivered when the user requests it.
Better performance: Because the FLV and SWF files are separate, the performance and results of your video playback will typically be better. Issues such as the lack of sync between the fps rate of the video and the fps rate of the SWF file will no longer be a problem.
These benefits apply to both progressive download and streaming video. They are compelling enough to warrant that embedded video should only be used as a last resort.
When comparing progressive download to streaming video, there's really only one benefit to progressive download: You don't need streaming server software to deliver the video. Progressive download video can be served from any normal web server. For example, it can be served off the same machine that is running Apache or IIS and serving your HTML pages.
While the progressive download approach is nice in that respect, you should note the following potential issues:
- Limited seek and navigation capabilities: Viewers cannot seek forward through the video before it is completely downloaded. Viewers need to wait until the video is downloaded before they can navigate to a particular portion of the video. Because of this, streaming video will probably be a better choice than progressive download when you are delivering long video files in which you want to let viewers skip around, such as lengthy symposia or training materials.
- User-accessible content: Because the file is downloaded, the media physically resides on the viewer's machine. Savvy users will be able to search their browser caches or temporary Internet files and access the content. This is not necessarily a bad thing if the content owner has no concerns about rights management for his or her content. In fact, in that case it may actually be useful—if the user decides to view the same video clip again before the browser cache is cleared, the file plays back from the local cache without the user having to access the web again. However, if digital rights are a concern, streaming video is a better option.
When to Use Progressive Download
Although we have clients who use progressive download for 30 minute TV shows without issues, progressive download is a perfect use for hobbyists or websites that have low traffic requirements and only need to deliver short videos. Customers who need advanced features and control over their video delivery—not to mention displaying video to large audiences (for example, several hundred simultaneous viewers), tracking and reporting video viewing statistics, or offering the best video experience—should consider streaming video.