Android AudioRecord 录制ENCODING_PCM_FLOAT AudioFormat格式音频以及与ENCODING_PCM_16BIT数据的转换

AudioRecord 录制ENCODING_PCM_FLOAT 格式音频

ENCODING_PCM_FLOAT 需要Android 23以上版本才支持。

• 构造AudioRecord。构造方法跟其他格式数据一致，只是audioFormat更改为AudioFormat.ENCODING_PCM_FLOAT。我这里传的数据格式为audioSource：MediaRecorder.AudioSource.MIC；sample：16000；channel：AudioFormat.CHANNEL_IN_MONO
• 录制对应音频。这里需要注意的是：录制ENCODING_PCM_FLOAT 格式的音频必须使用AudioRecord中对应的read方法：

    /**
     * Reads audio data from the audio hardware for recording into a float array.
     * The format specified in the AudioRecord constructor should be
     * {@link AudioFormat#ENCODING_PCM_FLOAT} to correspond to the data in the array.
     * @param audioData the array to which the recorded audio data is written.
     * @param offsetInFloats index in audioData from which the data is written.
     *        Must not be negative, or cause the data access to go out of bounds of the array.
     * @param sizeInFloats the number of requested floats.
     *        Must not be negative, or cause the data access to go out of bounds of the array.
     * @param readMode one of {@link #READ_BLOCKING}, {@link #READ_NON_BLOCKING}.
     *     
With {@link #READ_BLOCKING}, the read will block until all the requested data
     *     is read.
     *     
With {@link #READ_NON_BLOCKING}, the read will return immediately after
     *     reading as much audio data as possible without blocking.
     * @return zero or the positive number of floats that were read, or one of the following
     *    error codes. The number of floats will be a multiple of the channel count not to exceed
     *    sizeInFloats.
     * 

     * 
{@link #ERROR_INVALID_OPERATION} if the object isn't properly initialized
     * 
{@link #ERROR_BAD_VALUE} if the parameters don't resolve to valid data and indexes
     * 
{@link #ERROR_DEAD_OBJECT} if the object is not valid anymore and
     *    needs to be recreated. The dead object error code is not returned if some data was
     *    successfully transferred. In this case, the error is returned at the next read()
     * 
{@link #ERROR} in case of other error
     * 
     */
    public int read(@NonNull float[] audioData, int offsetInFloats, int sizeInFloats,
            @ReadMode int readMode) {

• audioData即为录制到的音频。

转换成ENCODING_PCM_16BIT

ENCODING_PCM_FLOAT 格式数据为32位IEEE浮点型数据。该如何转换成ENCODING_PCM_16BIT数据呢？16bit数据pcm的范围是-32768~32767.而PCM_FLOAT的数值范围为[-1,1)。对应关系一目了然即float[i]*32768就等于16bit数据中short值。
对应解析代码如下：

    private byte[] convertTo16Bit(float[] data) {
        short[] shortValue = new short[data.length];
        byte[] byte16bit = new byte[shortValue.length * 2];
        for (int i = 0; i < data.length; i++) {
            shortValue[i] = (short) (32768 * data[i]);
        }
        byte16bit = toByteArray(shortValue);
        return byte16bit;
    }

    private byte[] toByteArray(short[] src) {
        int count = src.length;
        byte[] dest = new byte[count << 1];
        for (int i = 0; i < count; i++) {
            dest[i * 2] = (byte) (src[i]);
            dest[i * 2 + 1] = (byte) (src[i] >> 8);
        }
        return dest;
    }