Java 无声 AudioFile 包含正文中的值

Question

我正在编写一个函数来标准化音频文件。我正在使用 JAudioTagger 库。

我在 Logic Pro X 中创建了一个简短的音频文件，它将完全静音(如果我理解正确的话，mp3 主体的所有字节都应该为 0)。

现在，当将 AudioFile 读入没有 header 的 byte[](长度为 4096 字节)时，主体包含一些值(其中一个最大为 (128))。

这里发生了什么？标题是否比预期的要长一些？或者逻辑会做一些疯狂的事情吗？

这是我的类(class)的代码:

public class AudioNormalizer {
    public static void normalizeAudioFile(AudioFile audioFile){
        byte[] audioInBytes = convertAudioFileToByteArray(audioFile);
        int maxValue = getMaxValue(audioInBytes);
    }

    public static byte[] convertAudioFileToByteArray(AudioFile audioFile) {

        if (audioFile instanceof MP3File){
            try {
                org.jaudiotagger.audio.mp3.MP3File mp3File = new org.jaudiotagger.audio.mp3.MP3File(audioFile.getFile());
                long startingByte = mp3File.getMP3StartByte(audioFile.getFile());
                System.out.println(startingByte);

                return getBytesFromPosition(audioFile.getFile(), startingByte);

            } catch (IOException e) {
                e.printStackTrace();
            } catch (TagException e) {
                e.printStackTrace();
            } catch (ReadOnlyFileException e) {
                e.printStackTrace();
            } catch (InvalidAudioFrameException e) {
                e.printStackTrace();
            }
        }
        return null;
    }

    private static int getMaxValue(byte[] theArray){
        int maxValue = 0;
        int tempValue = 0;
        for (int value : theArray){
            tempValue = value;
            if (tempValue < 0){
                tempValue = tempValue * -1;
            }
            if (maxValue < tempValue){
                maxValue = tempValue;
            }
        }
        return maxValue;
    }


    private static byte[] getBytesFromPosition(File file, long startingByte){
        FileInputStream fileStream = null;
        byte[] result;
        try {
            fileStream = new FileInputStream(file);

            // Instantiate array
            byte[] arr= new byte[(int)file.length()];
            result = new byte[arr.length - (int)startingByte];

            /// read All bytes of File stream
            fileStream.read(arr,0,arr.length);

            FileWriter fw = new FileWriter("testOut.txt");

            for (int i = 0; i < 8000; i++) {
                fw.write(i + " " + arr[i] + "\n");
            }

            fw.close();


            for (int i = 0; i < arr.length - startingByte; i++){
                result[i] = arr[i + (int)startingByte];
            }

            //for (int X : arr){
            //    System.out.print((char)X);
            //}

            return result;

        } catch (FileNotFoundException e) {
            e.printStackTrace();
        } catch (IOException e) {
            e.printStackTrace();
        }

        return null;
    }
}

这是字节数组的输出，它由数组索引和值组成(例如:4011(数组索引)100(值))。

4083 0
4084 0
4085 0
4086 0
4087 0
4088 0
4089 0
4090 0
4091 0
4092 0
4093 0
4094 0
4095 0
4096 -1 (Starting point of the body)
4097 -5
4098 -30
4099 64
4100 0
4101 0
4102 0
4103 0
4104 0
4105 55
4106 -128
4107 0
4108 0
4109 0
4110 0
4111 0
4112 6
4113 -16
4114 0
4115 0
4116 0
4117 0
4118 0
4119 0
4120 -34
4121 0
4122 0
4123 0 (The rest is all 0)

我希望有人能解释我做错了什么

Answer 1

您应该首先解码 MP3 文件，然后再获取音频数据，您在程序中看到的是经过编码的 mp3 数据，其中显然包含 mp3 压缩特定的数据，而不是全 0 表示静音:)。例如，有一个名为 http://www.javazoom.net/javalayer/javalayer.html 的库，它可以将 mp3 文件解码为音频数据样本。我只有一些在 Android 上尝试的代码:)

public void decode(String inFileName) throws Exception {
    // System.out.println("Play [" + inFileName + "]");
    // FileInputStream is = new FileInputStream(inFileName);
    ByteArrayOutputStream outStream = new ByteArrayOutputStream(1024);
    InputStream is = getAssets().open(inFileName);
    Bitstream bitstream = new Bitstream(is);

    Decoder decoder = new Decoder();
    boolean initialized = false;
    boolean done = false;
    while (!done) {
        outStream.reset();
        Header frameHeader = bitstream.readFrame();
        if (frameHeader == null) {
            done = true;
        } else {
            try {
                SampleBuffer output = (SampleBuffer) decoder.decodeFrame(frameHeader, bitstream);

            if (!initialized) {
                initialized = true;
                processStreamInfo(output.getChannelCount(), output.getSampleFrequency());
            }
            //
            // if (output.getSampleFrequency() != 44100
            // || output.getChannelCount() != 2) {
            // throw new Exception("mono or non-44100 MP3 not supported");
            // }

            short[] pcm = output.getBuffer();
            for (short s : pcm) {
                outStream.write(s & 0xff);
                outStream.write((s >> 8) & 0xff);
            }
            processPCM(outStream.toByteArray());
            } catch (Throwable t) {
                Log.e("Throwable", "MP3", t);
            }
        }
        bitstream.closeFrame();
    }

}

/**
 * Process the StreamInfo block.
 * 
 * @param streamInfo
 *            the StreamInfo block
 * @see org.kc7bfi.jflac.PCMProcessor#processStreamInfo(org.kc7bfi.jflac.metadata.StreamInfo)
 */
public void processStreamInfo(int channelCount, int frequency) {
    try {
        // android.compatibility.javax.sound.sampled.AudioFormat fmt =
        // streamInfo.getAudioFormat();
        int encoding = AudioFormat.ENCODING_PCM_16BIT;
        // if (fmt.getEncoding() ==
        // android.compatibility.javax.sound.sampled.AudioFormat.Encoding.PCM_SIGNED)
        // {
        // if (fmt.getSampleSizeInBits() == 16) {
        // encoding = AudioFormat.ENCODING_PCM_16BIT;
        // }
        // if (fmt.getSampleSizeInBits() == 8) {
        // encoding = AudioFormat.ENCODING_PCM_8BIT;
        // }
        // }
        int channels = channelCount == 1 ? AudioFormat.CHANNEL_CONFIGURATION_MONO : AudioFormat.CHANNEL_CONFIGURATION_STEREO;
        int bufferSize = 32768 * 4;
        audioTrack = new AudioTrack(AudioManager.STREAM_MUSIC, frequency, channels, encoding, bufferSize, AudioTrack.MODE_STREAM);
        audioTrack.play();
    } catch (Throwable t) {
        Log.e("t", "t", t);
    }

}

/**
 * Process the decoded PCM bytes.
 * 
 * @param pcm
 *            The decoded PCM data
 * @see org.kc7bfi.jflac.PCMProcessor#processPCM(org.kc7bfi.jflac.util.ByteSpace)
 */
public void processPCM(byte[] pcm) {
    if (writer==null) {
        writer = new PCMWriter();
        writer.setPriority(Thread.MAX_PRIORITY);
        writer.start();
    }
    data.add(pcm);
}