线性PCM 16位到8位

Question

我试着用苹果的例子"SpeakHere“的录音部分来达到我的目的。一切似乎都好，但我需要添加一个选项，实际上提供8位录音。这是根据规范，不允许任何音频设置，所以我需要某种形式的转换从16位。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));
    }
}

但老实说我不知道该怎么做。任何想法都会感激的。

Answer 1

为什么不尝试用类似的方法初始化音频队列呢？

    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;