Học Actionscript 3.0 - p 34 docx

Changing Sound Volume and Pan Chapter 11: Sound 309 and positive interim values reflect some degree of pan right. The following script sets the channel instance to a pan setting of full left: var trans:SoundTransform = new SoundTransform(); trans.pan = -1; channel.soundTransform = trans; To transform all playing sounds at once, substitute the specified channel with the master SoundMixer class. For example, the following script mutes all sounds: var trans:SoundTransform = new SoundTransform(); trans.volume = 0; SoundMixer.soundTransform = trans; Now let’s apply what we’ve learned to our ongoing player example. The fol- lowing code can be found in the player_transform.fla source file, and demon- strates both volume and pan by using mouse coordinates. Figure 11-2 shows how the mouse will affect the sound transformation. Moving the mouse left and right pans the sound left and right. Moving the mouse up and down fades the volume up and down. stage origin {x:0, y:0} default direction of increasing y values (will be inverted for usability using ActionScript) center of stage Figure 11-2. How the mouse affects sound volume and panning in the adaption made to the sound player project Line 104 creates a SoundTransform instance and lines 105 through 109 con- tain the onPlayProgress() function that will set and apply the transforma- tions. This function will be called from the enter frame event listener function created earlier, which we’ll adapt in a moment. Download from Wow! eBook <www.wowebook.com> Part IV: Sound and Video 310 Changing Sound Volume and Pan To set these changes with the mouse in a natural and intuitive way, we need to think about ActionScript mouse coordinates and apply a little math. Line 106 sets the volume based on the y-coordinate of the mouse. By dividing the current vertical mouse coordinate ( mouseY) by the stage height, we get a percentage change. For example, if the mouse were in the middle of the stage, the value would be 50 percent (0.5). This suits us just fine because the volume setting should be between 0 and 1. 103 //transformations 104 var trans:SoundTransform = new SoundTransform(); 105 function updateMouseTransform():void { 106 trans.volume = 1 - mouseY / stage.stageHeight; 107 trans.pan = mouseX / (stage.stageWidth / 2) - 1 108 channel.soundTransform = trans; 109 } However, y-coordinates in ActionScript increase by moving down, and we typically think of the values of a volume slider increasing as they go up. Therefore, we must subtract our percentage from 1 to get the correct value. For example, let’s say the mouseY is 100, and the stage is 400 pixels tall. Dividing 100 by 400 gives us 25 percent, but the mouse is near the top of the stage, which we think of as a higher volume when imagining a volume slider. By subtracting 0.25 from 1, we end up with 0.75, or 75 percent, which is what we want. Next, let’s look at calculating pan. Line 107 affects the pan. This calculation is similar to the volume calculation, but we need a value between –1 for full left and 1 for full right, and a value in the center of the stage should equate to 0. To find the middle of the stage, we need to divide the stage width by 2, and if we continually divide the hori- zontal location of the mouse ( mouseX) by that value, we get a range of 0 to 2. For example, using the default stage width of 550, the center would be 275. Far left is 0/275 (0), center is 275/275 (1) and far right is 550/275 (2). Because, we need a range of –1 to 1, we subtract 1 from the entire formula. After calculating the volume and pan values based on the mouse position, and altering the corresponding properties of the trans transform object you created (lines 106 and 107), all that remains is updating the soundTransform property of the desired channel (line 108). Now all we have to do is amend the onPlayProgress() function earlier in the script, to update the transform. The function spans lines 60 through 64 and we need to replace the earlier sound transformation placeholder comment with a call to the updateMouseTransform() function (shown in bold in the follow- ing example). Now when you test your movie, you should be able to vary the volume and pan of the playing sound by moving the mouse around the stage. 60 function onPlayProgress(evt:Event):void { 61 playBar.width = 100 * (channel.position / sndLength); 62 updateMouseTransform(); 63 //future home of amplitude meter adjustment; 64 } N O T E Again, if you want to transform every sound playing at a given moment, sim- ply substituting SoundMixer for the specific channel in line 108 will accom- plish the task. Download from Wow! eBook <www.wowebook.com> Reading ID3 Metadata from MP3 Sounds Chapter 11: Sound 311 Reading ID3 Metadata from MP3 Sounds When encoding MP3 files (compressing and saving the audio in the MP3 for- mat), most sound applications can inject metadata into the file, storing this data in tags established by the ID3 specification. The amount of metadata included is decided during the encoding process, usually by whomever is doing the encoding. The software itself, however, can add some information, such as the name and/or version of the encoding software. Accessing this information is accomplished via the ID3Info class. The sim- plest way to query a sound’s main ID3 tags is by using the named properties of the ID3Info instance found in every Sound object. This is found in every sound’s id3 property. For example, you can query the artist and song names of an MP3 file this way (again assuming a Sound instance called snd): snd.id3.artist; snd.id3.songName; There are seven tags supported in this direct fashion, as seen in Table 11-1. Table 11-1. The most common ID3 tags and their corresponding ActionScript property names ID3 2.0 tag ActionScript property COMM Sound.id3.comment TALB Sound.id3.album TCON Sound.id3.genre TIT2 Sound.id3.songName TPE1 Sound.id3.artist TRCK Sound.id3.track TYER Sound.id3.year The remainder of the supported tags can be accessed through the same id3 property of the Sound class, but using the tag’s four-character name. Table 11-2 shows supported tags that do not also have accompanying property names of their own. Accessing the beats-per-minute data, for example, would require the following syntax: snd.id3.TBPM; If you prefer a consistent approach, it’s also possible to access all ID3 tag information using the four-character tag names, including the seven tags that have their own dedicated property names. However, for quick access to the most commonly used properties, you will likely find the descriptive names to be more useful. N O T E Many audio applications can add ID3 tags to sounds, both during and after the encoding process. Apple’s free iTunes can tag and encode, and Pa-software’s share- ware ID3 Editor can inject tags into existing MP3s. Both are available for the Macintosh and Windows platforms. Download from Wow! eBook <www.wowebook.com> Part IV: Sound and Video 312 Reading ID3 Metadata from MP3 Sounds Table 11-2. Supported ID3 tags without dedicated ActionScript property names ID3 2.0 tag Description TBPM Beats per minute TCOM Composer TFLT File type TIT1 Content group description TIT3 Subtitle/description refinement TKEY Initial key TLAN Languages TLEN Length TMED Media type TOAL Original album/movie/show title TOFN Original filename TOLY Original lyricists/text writers TOPE Original artists/performers TORY Original release year TOWN File owner/licensee TPE2 Band/orchestra/accompaniment TPE3 Conductor/performer refinement TPE4 Interpreted, remixed, or otherwise modified by TPOS Disc/position in set TPUB Publisher TRDA Recording dates TRSN Internet radio station name TRSO Internet radio station owner TSIZ Size TSRC ISRC (international standard recording code) TSSE Software/hardware and settings used for encoding WXXX URL link frame Finally, it’s possible to output all ID3 tags using a type of for loop. The fol- lowing code, found in the player_id3.fla source file, continues our player example by first creating a text field to display the data (lines 111 through 118). Lines 120 through 127 then add a listener to the sound instance to listen for the Event.ID3 event. Line 122 pulls the ID3 information from the event argument. The for in loop in lines 123 through 126 is a little different than the for loop discussed in Chapter 2. Instead of looping through a finite number of times, it loops through all the properties of an object. It uses the property Download from Wow! eBook <www.wowebook.com> Visualizing Sound Data Chapter 11: Sound 313 name as a key, and pulls the property value from the object using that string. Lines 124 and 125 add each tag to the end of the field by concatenating a string and ending it with a new line character to jump down to the next line. 110 //id3 111 var id3Field:TextField = new TextField(); 112 id3Field.x = 140; 113 id3Field.y = 15; 114 id3Field.width = 340; 115 id3Field.height = 95; 116 id3Field.border = true; 117 id3Field.background = true; 118 addChild(id3Field); 119 120 snd.addEventListener(Event.ID3, onID3Info, false, 0, true); 121 function onID3Info(evt:Event):void { 122 var id3Properites:ID3Info = evt.target.id3; 123 for (var propertyName:String in id3Properites) { 124 id3Field.appendText("ID3 Tag " + propertyName + " = " + 125 id3Properites[propertyName] + "\n"); 126 } 127 } When ID3 information is detected and the listener function is triggered, an ID3Info object is created to store the incoming data. The for in loop in lines 123 through 126 walks through all the properties stored and, in this case, adds them to a text field on stage. The data could also be displayed in a cus- tom MP3 player interface, placed into a database to rank most often played songs, and so on. Visualizing Sound Data Mastering any language depends heavily on motivating yourself to practice it. This is especially true with programming languages, because code is difficult to work into day-to-day conversation. Finding as little as 15 minutes a day to experiment with ActionScript 3.0 will hasten your progress considerably, however, and visualizing sound data will make that practice time fly by. ActionScript 3.0 gives you access to raw sound data during playback, allowing you to synchronize visuals to amplitude or frequency spectrum information. Using the former, you might easily create peak meters, or animated speaker illustrations, that bounce or throb to the beat. With spectrum data, on the other hand, you can draw a waveform of the sound or depict the low-, mid-, and high-range frequency bands of a sound much like an equalizer display. Amplitude The terms amplitude and volume are often used interchangeably, but under- standing just a bit about these concepts can help clarify our task. Volume is probably a familiar idea. It’s a measure of the loudness or intensity of N O T E In all cases, if a tag has not been encoded into the MP3, querying the tag directly will return undefined as a value. Download from Wow! eBook <www.wowebook.com> Part IV: Sound and Video 314 Visualizing Sound Data a sound, and is somewhat subjective. Amplitude, on the other hand, is a physics property that more directly applies to a sound wave. It measures the distance of the peak of a sound wave from its baseline. Because a waveform can contain positive and negative values, amplitude can also be positive or negative, as a waveform’s peaks can be above and below its baseline. Peak amplitude is a specific measurement of amplitude, measuring from one peak of a sound wave to the next. Because it’s measuring between peaks, and not from a baseline, its value is always positive. In other words, peak amplitude is the absolute value, or nonnegative value, of amplitude, and is the kind of amplitude information ActionScript 3.0 will deliver in this example. Figure 11-3 shows both amplitudes in a hypothetical sound wave. Getting the amplitude of a sound channel requires only that you read its leftPeak and/or rightPeak properties depending on which stereo channel you want to visualize. These properties will be equal when mono sounds are playing. Assuming a SoundChannel instance called channel, the syntax is: channel.leftPeak; channel.rightPeak; These properties will return a value between 0 and 1 to represent the current amplitude. Conveniently, this is also the range of values used by such prop- erties as alpha, scaleX, and scaleY. Therefore, to create a basic amplitude meter, you need only manipulate the height of a movie clip. Imagine two movie clips that look like vertical bars 100 pixels high, with instance names leftMeter and rightMeter. Because the leftPeak or rightPeak values are always a fraction of 1, multiplying the full size of the meters by these values will cause the meter to vary between a height of 0 (at minimum volume) and 100 (at full volume). A leftPeak value of 0.5 will set the left meter to half- height, or 50 pixels. The following snippet shows this process in code. We’ll also use this same technique in our sound player project in just a moment. leftMeter.height = 100 * channel.leftPeak; rightMeter.height = 100 * channel.rightPeak; If you wanted something slightly less conventional, you might manipulate the scale of a graphic, rather than the height of a bar, with the amplitude values. For example, you could create a picture of a speaker that increased in size based on the amplitude values. Unlike a peak meter, however, you don’t want the speaker icons to disappear at 0 volume—a possible byproduct of setting the scale of the graphic to a dynamic value between 0 and 1, inclusive. Therefore, you can add the amplitude value to the graphic’s original scale of 1 (100 percent, or full size). The speakers, therefore, will remain unchanged during silence and potentially grow to twice their size at 100 percent ampli- tude—that is, a scale of 1 + 1, or 2. This approach is shown in the following code snippet, and a complete implementation of the code is found in the speakers_peak.fla source file. leftSpeaker.scaleX = leftSpeaker.scaleY = 1 + channel.leftPeak; rightSpeaker.scaleX = rightSpeaker.scaleY = 1 + channel.rightPeak; N O T E A simple way to distinguish ampli- tude and volume is to remember that amplitude will likely change over time even while a sound plays at a fixed volume. Think about a basic bass drum rhythm playing at full volume. As the beats progress, the peak amplitude will vary between 0 (no sound) and 1 (full amplitude). The peak amplitude of a bass drum kick might shoot up to 1 and then decay quickly back to 0, over and over again, but the volume remains constant. If you visualized this change in amplitude during playback, you’d end up with what are often called peak meters—meters that repeatedly display the maximum current amplitude. If you visualized full volume, you’d see a very boring straight line at 1. amplitude amplitude peak amplitude Figure 11-3. Amplitude and peak amplitude of a sound wave N O T E Remember that sound channels are akin to recording tracks, allowing multiple sound sources to be manipulated dis- cretely, and that stereo channels deliver only left and right separation of a spe- cific sound. A sound channel can contain mono or stereo sounds. Mono sounds will contain the same information in both channels. Download from Wow! eBook <www.wowebook.com> Visualizing Sound Data Chapter 11: Sound 315 Adding peak meters to the sound player Let’s add a pair of peak meters to the sound player project we’ve been devel- oping. The following code is found in player_peak.fla. Lines 129 through 139 create two sprites using the drawBar() method dis- cussed earlier—with one important difference. The bars are rotated –90 degrees so that they will expand upward, instead of to the right. Lines 141 through 144 update the scaleX of each peak meter. Note that we’re updating scaleX, even though it will look like the height of the meters is changing due to the rotation in lines 130 and 136. Figure 11-4 illustrates this idea. 128 //peak meters 129 var lPeak:Sprite = drawBar(0x009900); 130 lPeak.rotation = -90; 131 lPeak.x = 500; 132 lPeak.y = 110; 133 addChild(lPeak); 134 135 var rPeak:Sprite = drawBar(0x009900); 136 rPeak.rotation = -90; 137 rPeak.x = 520; 138 rPeak.y = 110; 139 addChild(rPeak); 140 141 function updatePeakMeters():void { 142 lPeak.scaleX = channel.leftPeak * 100; 143 rPeak.scaleX = channel.rightPeak * 100; 144 } As with the updateMouseTransform() function call in the “Changing Sound Volume and Pan” section, we must now update our peak meters in the onPlayProgress() function found earlier in the script. We’ll again replace a function placeholder comment, this time the amplitude meter adjustment comment found in line 63 with a call to the updatePeakMeters() function. 60 function onPlayProgress(evt:Event):void { 61 playBar.width = 100 * (channel.position / sndLength); 62 updateMouseTransform(); 63 updatePeakMeters(); 64 } Now when you test your file, you should see two peak meters in the upper- right corner of the stage, moving in sync with the music and visualizing the peak amplitude of the sound during playback. You may also notice that this visual feedback reflects the sound transformations made with your mouse. If, for example, you move the mouse to the upper-left corner of the stage, you will see larger peaks in the left meter. If you move your mouse across the top of the stage, you will see the peaks move from the left meter to the right meter to correspond with the panning of the sound. Finally, if you then move your mouse down the right side of the stage, you will see the peaks steadily diminish in size as the amplitudes of the sound diminish. adjusting width adjusting width adjusting width Figure 11-4. Adjusting the width of a sprite rotated –90 degrees appears to affect the height of the sprite Download from Wow! eBook <www.wowebook.com> Part IV: Sound and Video 316 Visualizing Sound Data Creating More Expressive Peak Meters Using Masks Just for fun, we’re going to show you a slightly more expressive peak meter, based on a meter that you might see on a home stereo. In case you’ve never seen a peak meter before, it’s usually a series of 6 to 10 consecutive lights, stacked vertically or placed end to end, which glow in sequence depending on the amplitude of the sound. Typically, low amplitudes reveal cool colors (green or blue) for acceptable amplitudes. Additional lights reveal warm colors (yellow or amber) as amplitudes increase to possible distortion levels. Finally, hot colors (red) are revealed when the amplitude exceeds acceptable levels. A representation of this type of meter is shown in the top illustration of Figure 11-5. Because of the color changes, we can’t simply adjust the width , height , scaleX , or scaleY properties of the meter. If we did that, we would invalidate the purpose of the color bands because all the colors would be visible all the time, even at low amplitudes. This can be seen in the bottom left illustration of Figure 11-5. We need, instead, to show only those colors representative of the amplitude, be they cool or hot, as seen in the bottom-right illustration of Figure 11-5. You can reveal only specific colors by creating a mask for the color bars, and scaling only the mask. The entire peak meter is a movie clip, within which are two discrete elements: the color bands and another movie clip used as a mask. (In our file, a third element serves as an outline but is not affected by ActionScript.) Because a mask dictates which part of the content is seen (rather than hiding that content), altering the size of the mask will reveal the desired portion of the color bars, as seen in Figure 11-6. The following code is included in multicolor_peak_meters.fla, which contains two instances of a movie clip that serves as our meter. The instances are called lPeak and rPeak, and the symbol contains the outline, mask, and color bars seen in Figure 11-6. The mask has an instance name of barMask. The first five lines cover the basic sound loading and playing tasks discussed earlier in the chapter. The code inside the listener function sets the vertical scale of the mask inside each meter to match the peak amplitudes of the left and right channels. var snd:Sound = new Sound(); snd.load(new URLRequest("song.mp3")); var channel:SoundChannel = new SoundChannel(); channel = snd.play(); addEventListener(Event.ENTER_FRAME, onLoop, false, 0, true); function onLoop(evt:Event):void { lPeak.barMask.scaleY = channel.leftPeak; rPeak.barMask.scaleY = channel.rightPeak; } Unlike the speaker example discussed earlier, we do want the colors in the peak meter to disappear during silent passages, so we can set the scaleY property directly to the values generated by the leftPeak and rightPeak properties. Though this example uses assets found in the library of an FLA, the learningactionscript3 package contains the PeakMeter class for creating multicolor peak meters entirely from code. The PeakMeter_Example.as document class, and the corresponding PeakMeter_ Example.fla file for Flash Professional users, demonstrate how to use the class. Figure 11-5. The color peak meter in use Figure 11-6. The component parts of the color peak meter Download from Wow! eBook <www.wowebook.com> Visualizing Sound Data Chapter 11: Sound 317 Sound Spectrum Data So far, we’ve been able to synchronize visuals with sound data by using the values returned by the leftPeak and rightPeak properties of the SoundChannel instance. With this information, we’ve already created peak meters to visualize the amplitude of a sound during playback—but there’s a lot more you can do. We discussed scaling a speaker, and you can just as easily change the alpha, x, y, or rotation properties of a display object. The peak_visualizations directory in the accompanying source code includes examples of each of these tasks. Even with a lot of creativity behind your efforts, however, you still only have two simultaneous values to work with when using peak amplitudes. Fortunately, ActionScript 3.0 provides another way to visualize sound by giving you access to spectrum data during playback. Audio spectrum data typically contains a mixture of frequency and amplitude information and can give you a visual snapshot of a sound at any moment. You can use this information to draw a sound wave or you can preprocess the information to look at amplitudes in the low, mid, and high frequency ranges—much like the visual feedback a home-stereo equalizer can give you. We’ll support both kinds of data, and we’ll do so in a class so that it’s easy to add waveform visualization to your own projects. Figure 11-7 shows an example of what our class can draw. It depicts the left stereo channel wave- form in green and the right stereo channel waveform in red. Storing and retrieving sound spectrum data Before we discuss the new class, let’s talk a little bit about how much data we’ll be using and how we’ll handle the load. Each time we retrieve the sound spectrum data, we’re going to do so using the computeSpectrum() method of the SoundMixer class. This method retrieves data from the sound in real time and places that data into a special kind of array called the ByteArray, which we’ll explain in a moment. Every time the method is called, we’ll be using 512 data values from the sound—256 for the left channel and 256 for the right channel—to draw our waveform. We’re going to use an enter frame event listener to call the method so, assuming the default Flash Professional frame rate of 24 frames per second, that means we’ll be using 12,288 values per second. What’s more, the computeSpectrum() method returns bytes, which are very small units of data. We need to work with decimal values like 0.5, which are also called floating-point numbers or floats. It takes 4 bytes to make a single float, and we need 12,288 floats per second. Therefore, our file will need to process 49,152 bytes per second! You don’t need to worry about any of this math, because you’ll soon see that it’s all handled for you. But it does help to understand the magnitude of what we’re going to be doing. Working your way through nearly 50,000 values per second isn’t trivial, so this is a potential performance issue. Figure 11-7. A visualization of left and right channel waveforms Download from Wow! eBook <www.wowebook.com> Part IV: Sound and Video 318 Visualizing Sound Data Storing the data and retrieving it quickly are challlenges handled by the ByteArray class. A byte array is an optimized array that can be used to store any kind of bytes. For example, we used the ByteArray as part of the process that saved an image in Chapter 9. It can also be used to read external file data, like the ZaaIL library mentioned in the same chapter, that reads unsupported image formats. In this case, we’re going to use a ByteArray instance to store sound data. The ByteArray class has special methods that make retrieving data fast and efficient. These methods will process a series of bytes and turn them into the data format you need, so you don’t have to. For instance, we need float values, rather than bytes. The readFloat() method will read four sequential bytes, translate them into a float, and return the data we need. What’s more, the method will automatically increment through the bytes so that you don’t have to update a loop counter when parsing the contents of the array. For example, think of an array called myByteArray that contains 12 bytes. If this data were stored in a normal array, you’d likely work through it using a for loop, and you’d have to increment the loop counter after each query. Using a byte array, however, the first time you execute myArray.readFloat(), it will read the first four bytes, return a float, and remain poised at byte 5 to continue parsing the array. With the next call of myArray.readFloat(), bytes 5 though 8 will be returned as a float—again with no manual incrementing of the array—and you’re now at byte 9 ready to continue. The computeSpectrum() method will populate our ByteArray for us, and the readFloat() method will automatically translate the bytes into the data format we need, so we’re ready to go. However, a second, optional parameter of the computeSpectrum() method will allow us to choose between two ways to analyze our sound. Drawing a waveform or frequency spectrum By default, the computeSpectrum() method will fill a byte array with values that will translate to floats between –1 and 1. These values will plot a waveform as it ascends above or descends below its baseline, as shown in Figure 11-7. However, a second, optional parameter called FFTMode will return the ampli- tude of individual frequencies, with values between 0 and 1. An FFT plot distributes positive amplitudes of different frequencies across the baseline, much like the visual feedback a home-stereo equalizer can give you. Low frequencies of each channel appear on the left, and high frequencies appear on the right, as seen in Figure 11-8. As previously described, our example exercise will draw a waveform. However, after you’ve successfully tested your code, experiment with setting the second parameter of the computeSpectrum() method to true to plot FFT frequency amplitudes. N O T E FFT refers to “Fast Fourier Transform,” a method for efficiently computing the component frequencies that make up a signal like a sound or light wave. Figure 11-8. Visualizing frequency values with an FFT display Download from Wow! eBook <www.wowebook.com> . Figure 1 1-4 illustrates this idea. 128 //peak meters 129 var lPeak:Sprite = drawBar(0x 009 900 ); 1 30 lPeak.rotation = - 90; 131 lPeak.x = 500 ; 132 lPeak.y = 1 10; 133 addChild(lPeak); 134 135 var rPeak:Sprite. rPeak:Sprite = drawBar(0x 009 900 ); 136 rPeak.rotation = - 90; 137 rPeak.x = 5 20; 138 rPeak.y = 1 10; 139 addChild(rPeak); 1 40 141 function updatePeakMeters():void { 142 lPeak.scaleX = channel.leftPeak. <www.wowebook.com> Part IV: Sound and Video 31 2 Reading ID3 Metadata from MP3 Sounds Table 1 1-2 . Supported ID3 tags without dedicated ActionScript property names ID3 2 .0 tag Description TBPM Beats per minute TCOM