节拍器。计时器、音乐和动画

我找到的唯一100%可靠的方法是通过CoreAudio或AudioToolbox进行设置: https://developer.apple.com/documentation/audiotoolbox 一种音频流数据提供程序,由iOS以固定的时间间隔调用,以向音频系统提供音频样本。

一开始它可能看起来令人望而生畏,但一旦你设置好了它,你就可以完全精确地控制为音频生成的内容。

这是我使用音频工具箱设置音频单元时使用的代码:

static AudioComponentInstance _audioUnit;
static int _outputAudioBus;

…

#pragma mark - Audio Unit

+(void)_activateAudioUnit
{
    [[AVAudioSession sharedInstance] setCategory:AVAudioSessionCategoryAmbient error:nil];
    if([self _createAudioUnitInstance]
       && [self _setupAudioUnitOutput]
       && [self _setupAudioUnitFormat]
       && [self _setupAudioUnitRenderCallback]
       && [self _initializeAudioUnit]
       && [self _startAudioUnit]
       )
    {
        [self _adjustOutputLatency];
//        NSLog(@"Audio unit initialized");
    }
}

+(BOOL)_createAudioUnitInstance
{
    // Describe audio component
    AudioComponentDescription desc;
    desc.componentType = kAudioUnitType_Output;
    desc.componentSubType = kAudioUnitSubType_RemoteIO;
    desc.componentFlags = 0;
    desc.componentFlagsMask = 0;
    desc.componentManufacturer = kAudioUnitManufacturer_Apple;
    AudioComponent inputComponent = AudioComponentFindNext(NULL, &desc);

    // Get audio units
    OSStatus status = AudioComponentInstanceNew(inputComponent, &_audioUnit);
    [self _logStatus:status step:@"instantiate"];
    return (status == noErr );
}

+(BOOL)_setupAudioUnitOutput
{
    UInt32 flag = 1;
    OSStatus status = AudioUnitSetProperty(_audioUnit,
                                  kAudioOutputUnitProperty_EnableIO,
                                  kAudioUnitScope_Output,
                                  _outputAudioBus,
                                  &flag,
                                  sizeof(flag));
    [self _logStatus:status step:@"set output bus"];
    return (status == noErr );
}

+(BOOL)_setupAudioUnitFormat
{
    AudioStreamBasicDescription audioFormat = {0};
    audioFormat.mSampleRate         = 44100.00;
    audioFormat.mFormatID           = kAudioFormatLinearPCM;
    audioFormat.mFormatFlags        = kAudioFormatFlagIsSignedInteger | kAudioFormatFlagIsPacked;
    audioFormat.mFramesPerPacket    = 1;
    audioFormat.mChannelsPerFrame   = 2;
    audioFormat.mBitsPerChannel     = 16;
    audioFormat.mBytesPerPacket     = 4;
    audioFormat.mBytesPerFrame      = 4;

    OSStatus status = AudioUnitSetProperty(_audioUnit,
                                           kAudioUnitProperty_StreamFormat,
                                           kAudioUnitScope_Input,
                                           _outputAudioBus,
                                           &audioFormat,
                                           sizeof(audioFormat));
    [self _logStatus:status step:@"set audio format"];
    return (status == noErr );
}

+(BOOL)_setupAudioUnitRenderCallback
{
    AURenderCallbackStruct audioCallback;
    audioCallback.inputProc = playbackCallback;
    audioCallback.inputProcRefCon = (__bridge void *)(self);
    OSStatus status = AudioUnitSetProperty(_audioUnit,
                                           kAudioUnitProperty_SetRenderCallback,
                                           kAudioUnitScope_Global,
                                           _outputAudioBus,
                                           &audioCallback,
                                           sizeof(audioCallback));
    [self _logStatus:status step:@"set render callback"];
    return (status == noErr);
}


+(BOOL)_initializeAudioUnit
{
    OSStatus status = AudioUnitInitialize(_audioUnit);
    [self _logStatus:status step:@"initialize"];
    return (status == noErr);
}

+(void)start
{
    [self clearFeeds];
    [self _startAudioUnit];
}

+(void)stop
{
    [self _stopAudioUnit];
}

+(BOOL)_startAudioUnit
{
    OSStatus status = AudioOutputUnitStart(_audioUnit);
    [self _logStatus:status step:@"start"];
    return (status == noErr);
}

+(BOOL)_stopAudioUnit
{
    OSStatus status = AudioOutputUnitStop(_audioUnit);
    [self _logStatus:status step:@"stop"];
    return (status == noErr);
}

+(void)_logStatus:(OSStatus)status step:(NSString *)step
{
    if( status != noErr )
    {
        NSLog(@"AudioUnit failed to %@, error: %d", step, (int)status);
    }
}

最后,一旦启动,我注册的音频回调将是提供音频的回调:

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

    @autoreleasepool {
        AudioBuffer *audioBuffer = ioData->mBuffers;

        // .. fill in audioBuffer with Metronome sample data, fill the in-between ticks with 0s
    }
    return noErr;
}

您可以使用声音编辑器,如Audacity: https://www.audacityteam.org/download/mac/ 要编辑您的文件并将其保存到原始的PCM单声道/立体声数据文件中,或者您可以使用AVFoundation库之一从任何支持的音频文件格式中检索音频样本。将您的示例加载到缓冲区中,跟踪您在音频回调帧之间的中断位置,并将节拍器示例与0交错输入。

这样做的好处是,您现在可以依靠iOS的音频工具箱来确定代码的优先级,这样音频动画和视图动画就不会相互干扰。

干杯,祝你好运!

我找到了一个解决方案,玩苹果 AVAudioEngine example HelloMetronome . 我明白主要的想法。 我得安排声音 并处理用户界面中的回调。使用任何计时器开始播放声音和更新用户界面都是绝对错误的。