线性PCM 16位到8位

Question

我正试图采用苹果示例中题为"SpeakHere"的录制部分来达到我的目的。一切似乎都很好，但我需要添加一个选项，它实际上提供8位录制。这是根据任何音频设置都不允许的规范，所以我需要从16位进行某种转换。我想我需要把它放在回调函数中。

// ____________________________________________________________________________________
// AudioQueue callback function, called when an input buffers has been filled.
void AQRecorder::MyInputBufferHandler(  void *                              inUserData,
                                        AudioQueueRef                       inAQ,
                                        AudioQueueBufferRef                 inBuffer,
                                        const AudioTimeStamp *              inStartTime,
                                        UInt32                              inNumPackets,
                                        const AudioStreamPacketDescription* inPacketDesc)
{
    AQRecorder *aqr = (AQRecorder *)inUserData;
    try {
        if (inNumPackets > 0) {
            // write packets to file
            XThrowIfError(AudioFileWritePackets(aqr->mRecordFile, FALSE, inBuffer->mAudioDataByteSize,
                                             inPacketDesc, aqr->mRecordPacket, &inNumPackets, inBuffer->mAudioData),
                       "AudioFileWritePackets failed");
            aqr->mRecordPacket += inNumPackets;
        }
        // if we're not stopping, re-enqueue the buffe so that it gets filled again
        if (aqr->IsRunning())
            XThrowIfError(AudioQueueEnqueueBuffer(inAQ, inBuffer, 0, NULL), "AudioQueueEnqueueBuffer failed");
    } catch (CAXException e) {
        char buf[256];
        fprintf(stderr, "Error: %s (%s)n", e.mOperation, e.FormatError(buf));
    }
}

但说实话，我不知道怎么做。任何想法都将不胜感激。

Answer 1

为什么不尝试用类似的东西初始化音频队列？

    aqData.mDataFormat.mFormatID = kAudioFormatLinearPCM;        // 2
    aqData.mDataFormat.mSampleRate = 44100.0;                    // 3
    aqData.mDataFormat.mChannelsPerFrame = 1;                    // 4
    aqData.mDataFormat.mBitsPerChannel = 8;                     // 5
    aqData.mDataFormat.mBytesPerPacket =                         // 6
    aqData.mDataFormat.mBytesPerFrame =
    aqData.mDataFormat.mChannelsPerFrame * sizeof (SInt8);
    aqData.mDataFormat.mFramesPerPacket = 1;                     // 7
    AudioFileTypeID fileType = kAudioFileAIFFType;               // 8
    aqData.mDataFormat.mFormatFlags =                            // 9
    kLinearPCMFormatFlagIsBigEndian
    | kLinearPCMFormatFlagIsSignedInteger
    | kLinearPCMFormatFlagIsPacked; 

Answer 2

经过大量的调查和尝试，我发现我不需要转换，只需要设置不同的格式标志。

mRecordFormat.mFormatFlags=kLinearPCMFormatFlagIsBigEndian；mRecordFormat.mBitsPerChannel=8；