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Chapter 14. Adding Sound to Your Movies > Using Streaming Sounds

Using Streaming Sounds

Streaming sounds are specifically geared for playback over the Web. When Sync is set to Stream, Flash breaks a sound into smaller sound clips. Flash synchronizes these subclips with specific frames of the movie—as many frames as are required to play the sound. Flash stops streaming sounds when playback reaches a new keyframe or an instruction to stop playing either that specific sound or all sounds. Unlike event sounds, which must download fully before they can play, streaming sounds can start playing after a few frames have downloaded. This makes streaming the best choice for long sounds, especially if you'll be delivering your movie over the Web.

The Mystery of Streaming Sound

When you choose Stream as the Sync setting for a sound, Flash divides that sound clip into smaller subclips and embeds them in individual frames. The movie's frame rate determines the subclips'size. In a movie with a frame rate of 10 frames per second (fps), for example, Flash divides streaming sounds into subclips that are a tenth of a second long. For every 10 frames, Flash plays 1 second of the sound.

Flash synchronizes the start of each subclip with a specific frame of the movie. If the sound plays back faster than the computer can draw frames, Flash sacrifices some visuals (doesn't draw some frames of the animation) so that sound and images match up as closely as possible. Streaming sound ensures, for example, that you hear the door slam when you see it swing shut—not a few seconds before. If the discrepancy between sound-playback speed and frame-drawing speed gets big enough, however, those dropped frames make the movie look jerky, just as it would if you set a low frame rate to begin with.



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