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  1. About Alpha Channels
  2. Shooting Alpha Video for Dummies
  3. Where to Learn More
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Shooting Alpha Video for Dummies

Green- and blue-screen technology is widely used in film and video for keying (short for chroma keying), which is the process of extracting a specific color range from a video and replacing that color with transparency (alpha).

This is the technique used to project weather maps behind the weatherman on the 6 o’clock news or to composite two scenes into one. To do this, you shoot video against a green- or blue-screen background and then remove it in the editing environment.

This process has been around for years, but now it is possible to use it to great effect in your Flash projects.

If you have both Adobe After Effect and Flash Professional 8, you can export FLV video directly from After Effects by using the Select File > Export > Macromedia Flash Video (FLV) menu. This menu opens the Flash Video Encoder settings dialog box, from which you can set the various FLV settings.

If you don’t have After Effects, you can also export to another video format that supports alpha channels and then use the Flash 8 Video Encoder to convert your file to the FLV format. Using the Flash Video Encoder has some benefits over the After Effects FLV Encoder option. For starters, the Flash 8 Video Encoder supports basic color correction, clip editing, cue points, crop and trim, and batch processing. Taken together, these capabilities can significantly improve your Flash video production and workflow.

However, perhaps the easiest method for getting alpha video into Flash is to use the Video Import Wizard. This wizard takes you through the following import process:

  1. Choose File > Import Video from the main menu. The first screen, Select Video, enables you to browse for your FLV file. Locate the video clip and click Next (see Figure 3).
    Figure 3

    Figure 3 Tell Flash where the video clip you want to import is located.

  2. The second screen, Deployment, enables you to specify how you want to deploy your video. See my Informit article, "Flash Video Delivery Options," for details on the five delivery options listed here.
    Figure 4

    Figure 4 Indicate the desired Flash video delivery option on the Deployment Screen of the Video Import Wizard.

  3. Next is the Encoding screen (this screen is skipped if you are importing an FLV video clip that has already been encoded). The Flash Video Encoder application has an identical dialog box.
  4. Click the Show Advanced Settings button and put a check in the Encode Alpha Channel option (see Figure 5). You can change the other settings as required; however, other than checking the Encode Alpha Channel option, the default settings will do the job for you here. The FLV file will be encoded with the alpha channel you established with After Effects or your video-editing application. Click the Next button.
    Figure 5

    Figure 5 FLV Export panel showing the Encode Alpha Channel option on the Encoding screen of the Flash Professional 8 Import Video Wizard

  5. The next screen is where you apply your skin to the video player. Select the skin you want from the pop-up menu and click Next (see Figure 6).
    Figure 6

    Figure 6 Set your desired skin for the FLVPlayback component here in the Skinning screen of the Video Import Wizard.

  6. That’s it! You will see a confirmation screen providing a summary of your import selections. Click Finish.

The FLVPlayback component icon will be placed on the Stage for you to work with, and a copy of the component will go into the Library. Notice that you can’t see a live preview of your FLV file in the Flash IDE, but need to publish your file to see the video clip playing.

The icon links to the external FLV file saved in the same location as the original video clip. If you encoded your FLV clip with the Flash Video Encoder application, the FLV must still be imported into Flash using the same Video Import Wizard. However, because the file has already been encoded and converted to the FLV format, the import process is streamlined; screen #4, the Encoding screen, will be skipped.

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