iphone - 音频单元中可能的输出采样率

我正在尝试为远程I / O音频单元的输入流设置不同的采样率(例如32kHz，24kHz等)。但是输出始终以以下采样率之一播放:
不管我设置了什么，都为22.05kHz，33.1kHz，11.0kHz。令人惊讶的是，当我在AudioUnitGetProperty上为kAudioUnitScope_Output调用kAudioUnitProperty_SampleRate时，它始终返回44.1kHz

- (void)startToneUnit
{
    AudioComponentDescription defaultOutputDescription;
    defaultOutputDescription.componentType = kAudioUnitType_Output;
    defaultOutputDescription.componentSubType = kAudioUnitSubType_RemoteIO;
    defaultOutputDescription.componentManufacturer = kAudioUnitManufacturer_Apple;
    defaultOutputDescription.componentFlags = 0;
    defaultOutputDescription.componentFlagsMask = 0;

        // Get the default playback output unit
    AudioComponent defaultOutput = AudioComponentFindNext(NULL, &defaultOutputDescription);
    NSAssert(defaultOutput, @"Can't find default output");

        // Create a new unit based on this that we'll use for output
    OSErr err = AudioComponentInstanceNew(defaultOutput, &toneUnit);
    NSAssert1(toneUnit, @"Error creating unit: %hd", err);

        // Set our tone rendering function on the unit
    AURenderCallbackStruct input;
    input.inputProc = RenderTone;
    input.inputProcRefCon = (__bridge void *)(self);
    err = AudioUnitSetProperty(toneUnit,
                               kAudioUnitProperty_SetRenderCallback,
                               kAudioUnitScope_Input,
                               0,
                               &input,
                               sizeof(input));
    NSAssert1(err == noErr, @"Error setting callback: %hd", err);

        // 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 = SAMPLE_RATE;
    streamFormat.mFormatID = kAudioFormatLinearPCM;
    streamFormat.mFormatFlags =
    kAudioFormatFlagsNativeFloatPacked;
    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));

    NSAssert1(err == noErr, @"Error setting stream format: %hd", err);

        // Stop changing parameters on the unit
    err = AudioUnitInitialize(toneUnit);
    NSAssert1(err == noErr, @"Error initializing unit: %hd", err);

        // Start playback
    err = AudioOutputUnitStart(toneUnit);
    NSAssert1(err == noErr, @"Error starting unit: %hd", err);

    Float64 outSampleRate = 0.0;
    UInt32 size = sizeof(Float64);
    AudioUnitGetProperty (toneUnit,
                          kAudioUnitProperty_SampleRate,
                          kAudioUnitScope_Output,
                          0,
                          &outSampleRate,
                          &size);
    NSLog(@"Output sample rate is now at %f Hz", outSampleRate);

   }

音频单元支持的所有可能的输出采样率是多少？任何有关Apple文档的参考都将非常有帮助

谢谢

最佳答案

通常，AudioUnit可以以您指定的任何采样率运行。 RemoteIO(或Mac OS X上的HAL)AudioUnits，作为硬件的外观，受到更多限制-变速时钟发生器，可以以任意采样率运行的采样率发生器非常昂贵，并且通常不适合电话:)

不同的iOS硬件，硬件模型或硬件产品线或修订版可能支持不同的采样率。 RemoteIO仅接受您请求的速率，并将板载转换器设置为最接近您请求的速率。您始终必须执行AudioUnitGetProperty才能查看实际得到的内容。如果要录制或以其他速率工作，则需要使用转换器插件。

关于iphone - 音频单元中可能的输出采样率，我们在Stack Overflow上找到一个类似的问题：https://stackoverflow.com/questions/15506414/