java中的wav幅度（立体声或更多通道）

Question

您好，有人知道如何在 Java 中找到 WAV 文件中的振幅吗？如果文件是立体声（或有更多通道），如何将数据放入数组中？

谢谢！

Answer 1

Processing a WAV file header

下一个技巧有点挑战，因为内部数据格式可能是多种数据类型。如果您正在查看您的经典 Windows WAV 文件，它可能只是 PCM 16 位或 8 位。这意味着，您可以轻松地将数据加载到字节或短数组中。

但是，您会发现其他格式。当你知道你拥有的类型时，谷歌它。您会找到大多数信息。

Answer 2

如何从 inputStream 打开 WAVE

// The WAVE-File-Reader of Java needs to reset on marks
final InputStream markSupportedInputStream;
if (inputStream.markSupported()) {
    markSupportedInputStream = inputStream;
} else {
    // BufferedInputStream wraps an InputStream, buffers the read data
    // and so it can reset on marks

    // Including RIFF header, format chunk and data chunk, standard
    // WAVE files have an overall header size of 44 bytes. 8192 Bytes should
    // be enough. Unconsidered are untypically chucks, like cue chunk,
    // playlist chunk etc.
    final int bufferSize = 8192;
    markSupportedInputStream = new BufferedInputStream(inputStream,
            bufferSize);
}

final AudioInputStream stream;
try {
    stream = AudioSystem.getAudioInputStream(markSupportedInputStream);
} catch (final UnsupportedAudioFileException e) {
    throw new UnsuportedFormatException();
}

final AudioFormat format = stream.getFormat();

final int numChannels = format.getChannels();

之后，典型的 WAVE 文件被 PCM 编码（还有其他编解码器，如浮点数）。您必须阅读来自markSupportedInputStream 的示例。

PCM 包含多种参数组合：(Mono|Stereo)、(Signed|Unsigned)、(8 Bit|16 Bit)、(Big Endian|Little Endian for more than 8 Bit)。您可以在format 对象上找出这一点，例如format.getChannels()。出于这个原因，我编写了一个PcmCodec 类，其中包含decodeUnsigned16BitLittleEndian(buffer, offset) 之类的方法。我将样本值标准化为 [-1,1]。

我是这样判断它是什么 PCM：

public static boolean isAudioFormatSupported(
        final @NonNull AudioFormat format) {
    final Encoding encoding = format.getEncoding();
    final int numChannels = format.getChannels();
    final int sampleSizeBits = format.getSampleSizeInBits();

    final boolean encodingSupported = (encoding == Encoding.PCM_SIGNED || encoding == Encoding.PCM_UNSIGNED);
    final boolean channelsSupported = (numChannels == AudioSystem.NOT_SPECIFIED
            || numChannels == 1 || numChannels == 2);
    final boolean sampleSizeSupported = (sampleSizeBits == AudioSystem.NOT_SPECIFIED
            || sampleSizeBits == 8 || sampleSizeBits == 16);

    return encodingSupported && channelsSupported && sampleSizeSupported;
}

@NonNull
private static Format toInternalFormat(final @NonNull AudioFormat audioFormat) {
    final Format internalFormat;

    if (audioFormat.getEncoding().equals(AudioFormat.Encoding.PCM_SIGNED)) {
        switch (audioFormat.getSampleSizeInBits()) {
        case 8:
            internalFormat = Format.SIGNED_8_BIT;
            break;
        case 16:
        case AudioSystem.NOT_SPECIFIED:
            if (audioFormat.isBigEndian()) {
                internalFormat = Format.SIGNED_16_BIT_BIG_ENDIAN;
            } else {
                internalFormat = Format.SIGNED_16_BIT_LITTLE_ENDIAN;
            }
            break;
        default:
            throw new AssertionError(audioFormat.getSampleSizeInBits()
                    + " Bit not supported");
        }
    } else if (audioFormat.getEncoding().equals(
            AudioFormat.Encoding.PCM_UNSIGNED)) {
        switch (audioFormat.getSampleSizeInBits()) {
        case 8:
            internalFormat = Format.UNSIGNED_8_BIT;
            break;
        case 16:
        case AudioSystem.NOT_SPECIFIED:
            if (audioFormat.isBigEndian()) {
                internalFormat = Format.UNSIGNED_16_BIT_BIG_ENDIAN;
            } else {
                internalFormat = Format.UNSIGNED_16_BIT_LITTLE_ENDIAN;
            }
            break;
        default:
            throw new AssertionError(audioFormat.getSampleSizeInBits()
                    + " Bit not supported");
        }
    } else {
        throw new AssertionError("Neither PCM_SIGNED nor PCM_UNSIGNED");
    }

    return internalFormat;
}

以下是我如何解码特殊 PCM 的示例： 您需要从markSupportedInputStream 读入一个字节数组（缓冲区）。之后，您可以解码字节：

public float decodeMono(final @NonNull byte[] buffer, final int offset) {
    final float sample;
    switch (format) {
    case SIGNED_8_BIT:
        sample = decodeSigned8Bit(buffer, offset);
        break;
    case UNSIGNED_8_BIT:
        sample = decodeUnsigned8Bit(buffer, offset);
        break;
    case SIGNED_16_BIT_BIG_ENDIAN:
        sample = decodeSigned16BitBigEndian(buffer, offset);
        break;
    case SIGNED_16_BIT_LITTLE_ENDIAN:
        sample = decodeSigned16BitLittleEndian(buffer, offset);
        break;
    case UNSIGNED_16_BIT_BIG_ENDIAN:
        sample = decodeUnsigned16BitBigEndian(buffer, offset);
        break;
    case UNSIGNED_16_BIT_LITTLE_ENDIAN:
        sample = decodeUnsigned16BitLittleEndian(buffer, offset);
        break;
    default:
        throw new AssertionError();
    }

    return Util.clamp(sample, -1f, 1f);
}

private static float decodeUnsigned16BitBigEndian(
        final @NonNull byte[] buffer, final int offset) {
    final byte lower, higher;
    higher = buffer[offset];
    lower = buffer[offset + 1];
    final int sampleInt = ((higher & 0xff) << 8 | lower & 0xff) - 0x8000;
    final float sample = (float) sampleInt / (float) 0x7fff;
    return sample;
}