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Hour 20. Optimizing Your Flash Site > Task: Use the Bandwidth Profiler to Judge...

Task: Use the Bandwidth Profiler to Judge Download Times

In this task you are introduced to how the Bandwidth Profiler can help you assess how a movie might play over the Internet. Here are the steps to follow:

Download the file “keyframing.fla” from my Web site. The address is: www.phillipkerman.com/teachyourself/sourcefiles/keyframing.fla. Do a Test Movie (Ctrl+Enter).

As the exported .swf plays, select View, Bandwidth Profiler (Ctrl+B). Notice that this is an option in the Flash Player, not the authoring tool. Therefore, you'll only see it while you're testing.

The Bandwidth Profiler provides information while the movie plays, as shown in Figure 20.6. You see data on the left and a graph on the right.

Figure 20.6. Vital statistics for your exported .swf are shown in the upper-left area of the Bandwidth Profiler.

Now you'll look at the first section of data, called Movie. Most of this information is simply a recap of the settings you can change in your source movie (such as dimensions and framerate). In addition, you'll see two values whose numbers will vary: Size (or file size) and Preload. When I tested this movie, I got a file size of 9KB (or exactly 9,760 bytes). Later, when you attempt to optimize this file, you'll see whether the size is reduced. Preload displays how many frames must “preload” (and how long that takes) before the movie will start playing. Of course, this depends on your user's Internet connection. The Bandwidth Profiler can make estimates such as preload time based on the modem settings (found under the Debug menu).

Go ahead and select the Debug menu. Notice that one of the modem types has a check mark (56K, by default). Change this to 14.4 (for 14.4KBps modems), and you'll see the Preload setting change from less than 1 second to nearly 4 seconds!

From the Debug menu, select Customize …, which opens the Custom Modem Settings dialog box, as shown in Figure 20.7. Here, you can modify the presets or create your own. Add an option for the common DSL bit rate of 256KBps. In the fourth field, change User Setting 4 to 256K (DSL) and the number in the bit rate column to 32000. Click OK.

Figure 20.7. The Custom Modem Settings dialog box lets you simulate any Internet connection speed.

Select your new setting from the Debug menu. You should see the preload time reduce to nearly nothing.

The Bandwidth Profiler lets you simulate exactly how long a movie takes to download at the bit rate selected from Debug. Select View, Show Streaming. The movie will start over, and you'll see a green progress bar move across the top of the graph. Change the bit rate to 14.4 (from the Debug menu) and try Show Streaming again. Even with this relatively basic movie, the current frame marker in the graph (an arrow) catches up to the green progress bar and must occasionally wait for the content to download. This isn't desirable, but it's an accurate representation of how this movie will look on a slow connection. (You'll learn ways to address this in the next task, “Improve a File with the Bandwidth Profiler's Help,” but for now you're just learning how to identify problems.)

There's one other feature you should investigate. Confirm the View menu has Frame by Frame Graph selected (or press Ctrl+F). The graph shows a vertical bar for the file size of each frame's contents. A tall bar means a frame has more data. The red horizontal line represents the sustained data transfer rate the current bit rate can maintain. In other words, if a frame's bar is higher than the red line, Flash may need to pause at that frame while it downloads. For example, in the Keyframing sample file, you'll notice relatively high bars at the beginning and through frame 20. This makes sense. Close the test movie and look at the source file. After frame 20, there's no new content introduced. The lack of any new data means less to download (see Figure 20.8).

Figure 20.8. After frame 20, nothing new appears onscreen (until frame 31). This means most data is downloaded by then (as shown in the Bandwidth Profiler).



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