Question

我正在尝试使用AudioStreamBasicDescription在AudioUnit中设置属性。我正在尝试设置声音数据的格式。返回的错误代码是-10868。它仅发生在iOS 3.1.3或更低版本上，但适用于3.2或更高版本。因此它可以在模拟器中运行，在运行4.2的iPod touch上运行，但不适用于第一代iPod touch。

当我尝试设置AudioUnit音调单元的格式时发生错误。代码看起来像这样（来自cocoawithlove.com）

// Set the format to 32 bit, single channel, floating point, linear PCM
const int four_bytes_per_float = 4;
const int eight_bits_per_byte = 8;
AudioStreamBasicDescription streamFormat;
streamFormat.mSampleRate = sampleRate;
streamFormat.mFormatID = kAudioFormatLinearPCM;
streamFormat.mFormatFlags = kAudioFormatFlagsNativeFloatPacked | kAudioFormatFlagIsNonInterleaved;
streamFormat.mBytesPerPacket = four_bytes_per_float;
streamFormat.mFramesPerPacket = 1;  
streamFormat.mBytesPerFrame = four_bytes_per_float;     
streamFormat.mChannelsPerFrame = 1; 
streamFormat.mBitsPerChannel = four_bytes_per_float * eight_bits_per_byte;
err = AudioUnitSetProperty (toneUnit,
                            kAudioUnitProperty_StreamFormat,
                            kAudioUnitScope_Input,
                            0,
                            &streamFormat,
                            sizeof(AudioStreamBasicDescription));
// err now has error code -10868

我在标题中检查过，此错误代码对应于错误“kAudioUnitErr_FormatNotSupported”。所以我想iOS 3.1上不支持我试图设置的格式？我在哪里可以找到支持的格式？我可以尝试其他格式的指针吗？

使用渲染回调：

OSStatus RenderTone(
    void *inRefCon, 
    AudioUnitRenderActionFlags *ioActionFlags, 
    const AudioTimeStamp *inTimeStamp, 
    UInt32 inBusNumber, 
    UInt32 inNumberFrames, 
    AudioBufferList *ioData)

{
    // Fixed amplitude is good enough for our purposes
    const double amplitude = 0.25;

    // Get the tone parameters out of the view controller
    ToneGeneratorViewController *viewController =
        (ToneGeneratorViewController *)inRefCon;
    double theta = viewController->theta;
    double theta_increment =
        2.0 * M_PI * viewController->frequency / viewController->sampleRate;

    // This is a mono tone generator so we only need the first buffer
    const int channel = 0;
    Float32 *buffer = (Float32 *)ioData->mBuffers[channel].mData;

    // Generate the samples
    for (UInt32 frame = 0; frame < inNumberFrames; frame++) 
    {
        buffer[frame] = sin(theta) * amplitude;

        theta += theta_increment;
        if (theta > 2.0 * M_PI)
        {
            theta -= 2.0 * M_PI;
        }
    }

    // Store the updated theta back in the view controller
    viewController->theta = theta;

    return noErr;
}

Answer 1

我认为主要问题是版本4.0之前的iOS上不支持浮点音频。我不确定ARM浮点支持是什么，但我建议使用其中一种固定点格式进行输入和输出。

AudioUnit设置属性错误（错误代码-10868）

1 个答案: