Recipe 17.9. Compressing Sounds in Your Movie (Optimizing Quality and File Size)

Problem

You want to add compression to the sounds in your Flash movie to optimize both the quality of the sounds as well as the file size of the exported movie.

Solution

Adjust the compression settings for each sound and/or the global compression settings for the movie.

Discussion

How you choose to compress and export the sound in your Flash movies makes a tremendous difference in the quality and file size of the resulting movie. And Flash gives you quite a lot of control over how you want to handle the sounds. You can affect the compression for each sound individually, and you can also apply moviewide, global sound compression settings. You can apply settings to each sound individually in order to assure that you maximize the quality of your sounds while also minimizing the required file size. Because each sound is generally quite different from another, no one setting will necessarily work best for all sounds. For example, you can generally apply much more compression to sounds that are voice-only than you can to sounds that include music.

In order to apply compression settings to each sound individually:

1. Locate the sound symbol in the library, and open the Sound Properties dialog box for that symbol. You can do this either by selecting Properties…from the menu that appears when you right-click/Control-click on the symbol in the library. Or you can select the symbol by clicking on it once in the library, and then choose Properties…from the library menu.

2. In the Sound Properties window, you will see a Compression menu in the Export Settings portion at the bottom. If the sound you initially imported was an MP3 file, the MP3 compression option will already be selected, and the Use Imported MP3 Quality checkbox will be checked. Otherwise, if the original sound file was of a different format, the Default compression option is selected by default.

3. Select the compression type you want to apply to the sound:

   
   

   Default

   The default compression uses the movie-wide, global sound compression settings.

   
   

   ADPCM

   This compression type was used in Flash 4 and earlier before Flash movies could use MP3 compression. Unless you are authoring to Flash 4 or earlier, use MP3 compression instead.

   
   

   MP3

   MP3 compression became available in Flash 5, and it offers the highest compression with the highest sound quality.

   
   

   Raw

   This setting allows you to export the sound without compression. You can still adjust the sample rate and convert stereo tracks to mono to decrease the file size somewhat. Exporting without compression is not recommended for the Web.

   
   

   Speech

   This compression is a special compression optimized for voice-only audio. In almost all cases, it is preferable instead to use MP3 compression.

4. Choose the compression settings and/or sampling rate. Depending on what compression type you select, you can choose from different compression options and/or sampling rate options. The higher the value that you choose for the bit rate (which is the compression setting), the higher the sound quality will be, but the file size also will increase.

5. With MP3 compression, you can also choose a Quality setting. This setting affects the speed at which the sound is compressed when you export the movie. The Fast value means that the sound exports faster, but with less sound quality. Likewise, the Medium setting offers medium export speeds and sound quality, and the Best setting offers the longest export speeds and the highest sound quality. Therefore, while testing use Fast, but for your final export use Best. The Quality setting does not affect file size.

6. Test the sound. When you have selected the compression type and settings, click on the Test button within the Sound Properties window to play back the sound once as it will sound in the exported movie. If you want to stop the sound before it has reached the end, click the Stop button.

7. If the sound is as you want it, then click the OK button. Otherwise, adjust the compression settings and test the sound until it is to your liking. Then click OK.

When you export your Flash movie, each Event or Start synchronized sound exports with its individual settings. However, for a given Flash movie, there can be only one sound stream. Therefore, Flash automatically mixes all your streamed sounds into a single stream, and applies a single compression setting to the whole stream. Flash determines what settings to use by applying the settings from whichever streamed sound has the highest settings. When discussing the highest settings, I am referring to the settings that result in the largest file size.

By setting the compression and export options for each sound in your library, you can create the most effective results it terms of optimized sound quality and file size. However, there are also reasons to apply global sound settings. For one thing, if there are many (or all) sounds in your movie to which you want to apply the same setting, it is more efficient to leave each of the individual sounds' compression types set to Default, and apply a global setting.

To set the global sound settings:

1. Open the Publish Settings dialog box. You can do this by choosing File Publish Settings.

2. Near the bottom of the window are two options: Audio Stream and Audio Event. If you click the Set button next to these options, you can set the default compression values for all sounds set to Stream or to Event (including Start).

3. When you click the Set button, Flash opens the Sound Settings dialog box. The compression settings in this window are the same as the compression settings in the Sound Properties window. Choose the settings you want to apply, and click OK.

Because Flash applies different settings to stream and event sounds, make sure to modify the global settings for both Stream Audio and Event Audio. And remember that the global settings are only applied to sounds that have default compression applied to them individually. Otherwise, the individual sound compression settings take precedence over the global settings.

Another good reason to apply global sound settings is that you can choose to override the individual sound compression settings. This approach is particularly useful if you want to quickly export a movie with different sound settings without having to modify each individual sound's properties. For example, if you have applied settings to your movie in order to optimize it for the Web, but you want to also quickly export a version with higher sound quality for a CD-ROM, you can choose to do so with a single checkbox option. In the Publish Settings window, check the Override Sound Settings option, and Flash will automatically apply the global sound settings to all sounds.