ios - 我想每秒调用 20 次 installTapOnBus :bufferSize:format:block:

Question

我想在麦克风的实时输入中显示波形。我是用installTapOnBus:bufferSize:format:block:实现的，这个函数一秒调用了3次。我想将此函数设置为每秒调用 20 次。在哪里可以设置？

AVAudioSession *audioSession = [AVAudioSession sharedInstance];

NSError* error = nil;
if (audioSession.isInputAvailable) [audioSession setCategory:AVAudioSessionCategoryPlayAndRecord error:&error];
if(error){
    return;
}

[audioSession setActive:YES error:&error];
if(error){
    retur;
}

self.engine = [[[AVAudioEngine alloc] init] autorelease];

AVAudioMixerNode* mixer = [self.engine mainMixerNode];
AVAudioInputNode* input = [self.engine inputNode];
[self.engine connect:input to:mixer format:[input inputFormatForBus:0]];

// tap ... 1 call in 16537Frames
// It does not change even if you change the bufferSize
[input installTapOnBus:0 bufferSize:4096 format:[input inputFormatForBus:0] block:^(AVAudioPCMBuffer* buffer, AVAudioTime* when) {

    for (UInt32 i = 0; i < buffer.audioBufferList->mNumberBuffers; i++) {
        Float32 *data = buffer.audioBufferList->mBuffers[i].mData;
        UInt32 frames = buffer.audioBufferList->mBuffers[i].mDataByteSize / sizeof(Float32);

        // create waveform
        ...
    }
}];

[self.engine startAndReturnError:&error];
if (error) {
    return;
}

Answer 1

他们说，Apple 支持回复否:(2014 年 9 月)

Yes, currently internally we have a fixed tap buffer size (0.375s), and the client specified buffer size for the tap is not taking effect.

但有人调整缓冲区大小并获得 40 毫秒 https://devforums.apple.com/thread/249510?tstart=0

无法检查它，在 ObjC 中 :(

UPD 它有效!只是单行:

    [input installTapOnBus:0 bufferSize:1024 format:[mixer outputFormatForBus:0] block:^(AVAudioPCMBuffer *buffer, AVAudioTime *when) {
    buffer.frameLength = 1024; //here