Iphone AudioFileWriteBytes失败，错误代码为-40

我正在尝试使用AudioFileWriteBytes（）将原始音频字节写入文件。以下是我正在做的：

void writeSingleChannelRingBufferDataToFileAsSInt16(AudioFileID audioFileID, AudioConverterRef audioConverter, ringBuffer *rb, SInt16 *holdingBuffer) {
// First, figure out which bits of audio we'll be 
// writing to file from the ring buffer

    UInt32 lastFreshSample = rb->lastWrittenIndex;
    OSStatus status;
    int numSamplesToWrite;
    UInt32 numBytesToWrite;


    if (lastFreshSample < rb->lastReadIndex) {
        numSamplesToWrite = kNumPointsInWave + lastFreshSample - rb->lastReadIndex - 1;
    }
    else {
        numSamplesToWrite = lastFreshSample - rb->lastReadIndex;
    }
    numBytesToWrite = numSamplesToWrite*sizeof(SInt16);

---

这个错误是什么-40？顺便说一句，如果我直接从ringBuffer写入文件，一切都很好。当然，这听起来像垃圾，因为我在写浮动，而不是SInt16s，但AudioFileWriteBytes并不抱怨

关键是将传入数据的endian显式更改为big endian。我所要做的就是将CFSwapInt16HostToBig包裹在我的数据周围，以获得：

float audioVal = rb->data[(i + rb->lastReadIndex) & buffLen];
holdingBuffer[i] = CFSwapInt16HostToBig((SInt16) audioVal );

    status = AudioFileWriteBytes(audioFileID, NO, 0, &numBytesToWrite, &holdingBuffer);     
    rb->lastReadIndex = lastFreshSample;

    NSLog(@"Error = %d, wrote %d bytes", status, numBytesToWrite); 

    return;

float audioVal = rb->data[(i + rb->lastReadIndex) & buffLen];
holdingBuffer[i] = CFSwapInt16HostToBig((SInt16) audioVal );