You can import a variety of file formats into Flash, which supports uncompressed and compressed sound. The most common formats are WAV, AIFF, and MP3; all three are supported on both Windows and Mac. WAV and AIFF files are typically used for uncompressed sounds, although you can use compression when creating both formats. MP3 files are for compressed sounds (specific compression algorithms will be discussed in a moment).

Additional file formats are supported when QuickTime 4.0 or later is installed. AU (Sun Audio) and MOV (sound-only QuickTime movie) files can be imported on Windows and the Mac, and SD2 (Sound Designer 2) and SFIL (System 7 Sounds) can be imported on the Mac only.

Importing a sound is the same as importing graphical assets, with one exception. Because there is no visual component to an audio file, the Import to Stage option functions just like the Import to Library option. When you import a sound, Flash automatically places it in the Library and adds nothing to the Stage or Timeline (you’ll learn to use the sound in your files in the Timeline Use and ActionScript Use sections, later in this chapter).

For widest compatibility, only MP3 files can be loaded from external sources and played at runtime. However, as of Flash Player 9 Update 3, released in December 2007, file formats using the AAC compression scheme are also supported for runtime playback. Apple’s iTunes and compatible hardware (iPods, iTouch, iPhone), Sony’s Playstation, and Nintendo’s Wii platforms use AAC. The most common file types using AAC are M4A, MP4 and AAC.

Although the current Flash Player supports AAC, the most popular external compressed file format remains MP3. There are dozens of applications that compress MP3 sounds, and they are the most common audio files used on electronic sound players such as iPods.

Apple’s iTunes, the primary application used to sync with iPods, is a free, cross-platform application that can compress sounds using many Flash-compatible formats, including MP3, WAVE, AIFF, and AAC files like M4A. See this book’s companion website for examples of how to create audio files using iTunes.

When compressing audio, another key term comes into play. Bitrate represents the number of bits transferred per second. Bitrate is not a term specific to audio, but pertains to the transfer of any digital data. It surfaces frequently in discussions about audio because it is also a measure of the quality of compressed sound. In addition to bit depth and sample rate, a high bitrate contributes to higher-quality sound. As a point of comparison, a very high-quality MP3 bitrate is 320 kbps (kilobits per second, or 1,000 bits for every second of sound), a good bitrate is 128 kbps, and a low-quality sound is 16 kbps.

The most important things to remember when compressing sounds are:

The highest degree of control you can exert over sound quality and file size comes from applying compression on a sound-by-sound basis. Once you have imported a sound, you can select it in the Library and access its properties using the Properties button (i icon) at the bottom of the Library panel.

The Sound Properties dialog (Figure 12-1) allows you to change the compression and, where applicable, convert stereo to mono (termed Preprocessing in the dialog because it occurs prior to compression), and change the Bit rate, Sample rate, and Quality of compression. The latter is an arbitrary measure that includes Fast, Better, and Best, and determines how long the compression takes.

Figure 12-1. Per-file sound properties

Compression options include:

Using your file’s publishing settings (File→Publish Settings), you can specify compression settings that can be applied to every sound in the entire file. This only occurs when compiling the file’s SWF.

You can specify settings for streaming sounds (sounds that play while still being downloaded) and event sounds (sounds that must be fully downloaded before playback begins). The streaming option is best for larger sounds that take a long time to download, while event sounds are better suited for very short sounds that can easily be downloaded and fit into memory. Additional options will be discussed later in the Sync Types section of this chapter.

Because of their different uses, you can apply independent compression settings to each type of sound. This lets you choose a higher-quality setting for streaming sounds and a lower-quality setting for event sounds that must be small enough to download quickly. You can configure these settings in the Images and Sounds section of the Publish Settings dialog (Figure 12-2).

Figure 12-2. File-wide sound-related publish settings

The Sound Settings dialog (Figure 12-3) offers access to the same compression algorithms available on a per-file basis. The Default per-sound option, which specifies that these global settings should be used for a specific sound, has been replaced in Publish Settings with Disable. This option disables all sound in the SWF and is useful for testing or creating alternate versions of your file with no audio.

Figure 12-3. Compression options for internal sounds applied file-wide

At the bottom of the Publish Settings section (refer back to Figure 12-2), you can choose to override the sound settings. When you enable the Override sound settings option, Flash will override the per-asset sound settings and apply the global Publish Settings instead. This is useful for creating a low-quality alternate version of your file. You can also use this option to speed up SWF compilation during testing by switching to a Fast quality setting. When you’re finished with development and ready to publish your final file, you can disable the override option, and the per-sound settings will be reapplied.

Finally, you can enable the Export device sounds option to support Flash Lite development, not covered in this book.

The Sync type you set in the Properties panel for a Timeline-based sound will have a dramatic effect on how the sound plays. With the sound frame in the Timeline panel selected, the Properties panel shows the following four sync types.

With a sound frame selected in the Timeline panel, you can loop a sound or repeat it a finite number of times by using the menu and repeat count input below the Sync menu (Figure 12-7). Loop will show no visual change in the Timeline, but will loop the sound as long as the playhead is in contact with the frames in which the sound resides. Repeat will play the sound again as many times as you specify using the repeat count. It will also repeat the waveform in the Timeline a corresponding number of times (Figure 12-8).

Figure 12-7. Repeating a sound

Figure 12-8. A repeating sound displayed in the Timeline

When you choose Custom from the Effect menu or edit a preset, the Edit Envelope dialog opens. Figure 12-9 shows the dialog with the Fade Out preset. To edit the volume or pan of the sound, first click on the horizontal line that runs across the waveform to add a handle. In stereo sounds, a handle will be created in both the left (top) and right (bottom) channels. In any channel, you can then drag the handles down or up to reduce or increase volume, respectively.

Figure 12-9. Fading a sound in the Edit Envelope dialog

Figure 12-9 shows a reduction in volume at the end of the sound, as both channels fade to 0. Figure 12-10 shows a change in pan as the sound moves from the left to right channels. The volume is decreased in the left channel and simultaneously increased in the right channel.

Figure 12-10. Panning a sound from left to right

During editing, you can test your work without leaving the dialog or testing your movie. Simply use the stop and play buttons in the lower-left corner of the dialog to audition your effect. No changes are made to the original file, so you can experiment to your liking.

In the lower-right corner of the dialog, you can zoom in and out of the waveform (clicking the magnifying glass icons) and switch between a time-based (watch icon) or frame-based (movie icon) display. The latter two options change the horizontal numbered strip between the channels to show either frames or seconds. In Figure 12-9, for example, the sound starts to fade at three seconds, and is muted by the fourth second.

Flash even provides a convenient workflow for editing your sounds in an external sound editor. Control+clicking (Mac) or right-clicking (Windows) on a sound asset in the Library displays a context-sensitive menu that reveals editing options. Figure 12-11 illustrates your editing choices: the cross-platform, open source editor Audacity; an editor you select on the fly; or Adobe Sound booth, an entry-level sound editor targeted at Flash users.

Figure 12-11. Editing a sound in an external application

When you select one of these options, the sound opens in the selected external editor so you can then edit the file. When you save the file, it will automatically be updated in Flash.

Playing an embedded sound from the Library is very similar to adding a symbol instance to the display list. The process begins by assigning the sound a Linkage class (Figure 12-12).

Figure 12-12. Assigning a sound’s Linkage class

Your file should play a short beep sound from the embedded beep.wav file. If needed, compare your file with the furnished play_embedded_sound.fla file.

In addition to playing embedded sounds, you can load external audio files to play at runtime. This is advantageous for many reasons, including reducing SWF file size and making it easier to edit, update, or replace the external file.

The following exercise will span the next three sections of this chapter, adding functionality to your script as the chapter progresses:

Now when the sound finishes loading, the complete event will be dispatched. When the event is received, the sound will play again from the beginning, into the same channel.

With regard to line numbering, the next two sections of this exercise assume this option was not added. If you chose to play the sound upon loading, adjust your file’s line numbers accordingly.

You set the volume of a sound using a range of 0 to 1. A value of 0 mutes a sound and a value of 1 sets the sound to full volume. The pan of a sound is set using a slightly different scale, from −1 to 1. The sound pan can be centered (0), entirely in the left channel (−1), or entirely in the right channel (1).

The final topic covered in this chapter lets you visually represent the volume of an audio file during playback. Two properties of the SoundChannel instance, leftPeak and rightPeak, contain the volume of the left stereo channel and right stereo channel, respectively (when analyzing monaural sounds, both values are equal).

In this example, two circles that represent left and right stereo speakers will expand and contract with the sound channel’s volume during sound playback:

This script creates an event listener that listens for an enter frame event (lines 11 and 13) and adjusts the scaleX and scaleY of each speaker based on the volume of the sound channel’s left and right stereo channels, respectively.

Instead of setting these properties to the leftPeak and rightPeak values directly, they are added to a value of 1. This prevents the speakers from shrinking, possibly to a scale of 0, during quiet portions of the audio. That is, rather than displaying scales that correspond with volumes of 0, 0.5, and 1, the resulting scales are 1, 1.5, and 2. When the volume is muted, the speaker size is 100%, and at full volume the speaker size is 200%, or double the original dimensions.

In prior chapters, you created the sound controller and integrated it into the master project file. The following script will load an external MP3 file, toggle between playing and disabled states, and visualize the amplitude of the left and right stereo channels.

Open your master portfolio FLA and add the following script to the frame 99 of the actions layer. Frame 99 is the last intro frame (prior to the Home screen) and initializes both the navigation and sound controls:

1 var snd:Sound = new Sound();
2 snd.load(new URLRequest("assets/song.mp3"));
3
4 var channel:SoundChannel = new SoundChannel();
5 channel = snd.play();
6
7 this.addEventListener(Event.ENTER_FRAME, onSoundPlayback);
8 function onSoundPlayback(evt:Event):void {
9    soundControl.lPeak.barMask.scaleX = channel.leftPeak * 4;
10   soundControl.rPeak.barMask.scaleX = channel.rightPeak * 4;
11 }
12
13 soundControl.addEventListener(MouseEvent.CLICK, onSoundToggle);
14 function onSoundToggle(evt:MouseEvent):void {
15    if (channel.leftPeak > 0) {
16        channel.stop();
17    } else {
18        channel = snd.play();
19    }
20 }

Lines 1 through 5 load and play a sound, as described in the Playing an External Sound section, earlier in this chapter. The only difference here is that, for the portfolio project, you are placing the sound file in your external assets directory, with the other external assets used throughout the book.

Lines 7 through 11 visualize the volume of the sound’s left and right stereo channels. To understand how this script works, it helps to recall the structure of the sound controller movie clip from Chapter 3. It has an instance name of soundControl and contains two child instances of a volume meter, one for each channel, named lPeak and rPeak. Within the meter is another movie clip named barMask that sits in a mask layer. By manipulating the scaleX property of the mask movie clip (lines 9 and 10), you expose different widths of the meter, and therefore different temperatures of color, during sound playback. Every enter frame (lines 7 and 8), the leftPeak and rightPeak properties return a percentage value, between 0 and 1, of the full volume of each channel.

When playing relatively quiet sounds, your visualization meter may appear a bit listless. If you want to liven things up a bit, you can increase the effect the actual peak values have on your artwork. Simply multiply the values of the leftPeak and rightPeak properties by an adjustment factor, as seen in lines 9 and 10. For example, these lines multiply low-level settings of 0.1 by 4 to become 0.4. The larger values increase the widths of the masks, showing larger meters.

Lines 13 through 20 toggle the sound playback states. With every mouse click (lines 13 and 14), a simple test is performed. If there is any volume in the left channel, the sound is stopped. If the left channel is silent, the sound is played again from the beginning. This basic script lets you turn the sound on and off.

In the next chapter, you will encode video, review its use in the project’s Gallery screen, and learn ActionScript alternatives for displaying and controlling video in your own files.