ByteBuffer.array() returns 比 byteBuffer 更大的数组 Android

Question

基本上我有以下场景：

inputByteBuffer (capacity in debug) => 1024
byte[] inByteBufferArray = inputByteBuffer.array();
inByteBufferArray.length => 1031 ????

ByteBuffer array() 方法说明了 "Returns the byte array which this buffer is based on, if there is one." ref

这是在 Android API 18 年工作的，有什么变化吗？有一个 ByterBuffer arrayOffset() 方法，我需要那个吗？

这是在 Nexus 6 设备上发生的，但我认为这无关紧要。

谢谢

private static int bufferSizeStatic = 1024;

private float[] Read(){
        mAudioRecord.read(inputByteBuffer, bufferSize);
        return readByteArray(inputByteBuffer.array(), inputByteBuffer.arrayOffset());
}

private float[] readByteArray(byte[] byteArray, int offSet) {
        if (floatArray == null || floatArray.length!=(byteArray.length-offSet) / (numChannels*numBytePerFrame)){
            floatArray = new float[(byteArray.length-offSet) / (numChannels*numBytePerFrame)];
        }

        if (numChannels == 1){
            for (int i = 0; i < floatArray.length; i++){
                short tempShort = (short) ((byteArray[2*i+1+offSet]<<8) + byteArray[2*i+offSet]);
                floatArray[i] = (float) (tempShort / Math.pow(2,15)); 
            } 
        } //TODO add stereo support
        return floatArray;
    }

Answer 1

我不明白你为什么关心。您的代码当然不应该关心。它这样做的唯一原因是因为您滥用了 API。您不应该从不在其中的缓冲区中获取数据，这些数据由 limit(), 而不是 array().length() 或 capacity() 给出。

你只需要调整调用顺序，直接使用ByteBuffer：

private static int bufferSizeStatic = 1024;

private float[] Read(){
    // I don't know why you need to pass `bufferSize` here: `inputByteBuffer` already knows its own limit
        mAudioRecord.read(inputByteBuffer, bufferSize);
        return readByteArray(inputByteBuffer);
}

private float[] readByteArray(ByteBuffer byteBuffer) {
        if (floatArray == null || floatArray.length!=(byteArray.limit()-byteArray.position()) / (numChannels*numBytePerFrame)){
            floatArray = new float[(byteArray.limit()-byteArray.position()) / (numChannels*numBytePerFrame)];
        }

        byteBuffer.flip();
        if (numChannels == 1){
            for (int i = 0; i < floatArray.length; i++){
                short tempShort = (short) ((ByteBuffer.getShort(i*2));
                floatArray[i] = (float) (tempShort / 32768.0); 
            } 
        } //TODO add stereo support
        byteBuffer.compact();
        return floatArray;
    }

E&OE

您会发现这至少同样有效。

Answer 2

我找到了 android 代码：

MemoryRef(int capacity) {
    VMRuntime runtime = VMRuntime.getRuntime();
    buffer  = (byte[])runtime.newNonMovableArray(byte.class, capacity + 7);
    allocatedAddress = runtime.addressOf(buffer);
    // Offset is set to handle the alignment: http://b/16449607
    offset = (int)(((allocatedAddress + 7) & ~(long)7) - allocatedAddress);
    isAccessible = true;
}

来源在这里： https://android.googlesource.com/platform/libcore/+/fe0e5d3e460de87d24e0224ef10b089289355c47/ojluni/src/main/java/java/nio/DirectByteBuffer.java#60

ByteBuffer.array() returns 比 byteBuffer 更大的数组 Android

ByteBuffer.array() returns a larger array than byteBuffer Android

java

arrays

android

bytebuffer