ios – 完成音频队列播放的精确时间

我找到了一种更简单的方法来获得相同的结果(/ -10ms).使用AudioQueueNewOutput()设置输出队列后,初始化要在输出回调中使用的AudioQueueTimelineRef. (我的第一个方法中包含ticksToSeconds函数)不要忘记导入< mach / mach_time.h>@H_675_4@

//After AudioQueueNewOutput()
AudioQueueTimelineRef timeLine;     //ivar
AudioQueueCreateTimeline(queue,self.timeLinE);

然后在输出回调中调用AudioQueueGetCurrentTime().警告：队列必须播放有效的时间戳.因此,对于非常短的文件,您可能需要使用下面的AudioQueueProcessingTap方法.@H_675_4@

Audiotimestamp timestamp;
AudioQueueGetCurrentTime(queue,self->timeLine,&timestamp,null);

时间戳将当前播放的样本与当前机器时间联系在一起.有了这些信息,我们可以在将来播放最后一个样本时获得准确的机器时间.@H_675_4@

Float64 samplesLeft    = self->frameCount - timestamp.mSampleTime;//samples in file - current sample
Float64 secondsLeft    = samplesLeft / self->sampleRate;          //seconds of audio to play
UInt64  ticksLeft      = secondsLeft / ticksToSeconds();          //seconds converted to machine ticks  
UInt64  machTimeFinish = timestamp.mHostTime + ticksLeft;         //machine time of first sample + ticks left

现在我们拥有了这个未来的机器时间,我们可以使用它来准确地计算您想要做的任何事情.@H_675_4@

UInt64 currentMachTime = mach_absolute_time();
Uint64 ticksFromNow = machTimeFinish - currentMachTime;
float secondsFromNow = ticksFromNow * ticksToSeconds();
dispatch_after(dispatch_time(DISPATCH_TIME_Now,(int64_t)(secondsFromNow * NSEC_PER_SEC)),dispatch_get_main_queue(),^{
    //do the thing!!!
    printf("Giggety");
});

如果GCD dispatch_async不够准确,有办法设置precision timer@H_675_4@

使用AudioQueueProcessingTap@H_675_4@

您可以从AudioQueueProcessingTap获得相当低的响应时间.首先,你的回调基本上会置于音频流之间. MyObject类型就是代码中的self(这是ARC桥接在这里以获得函数内部的自我).检查ioFlags会告诉您流何时开始并完成.输出回调的iotimestamp描述了回调中的第一个样本将来会触及发言者的时间.所以,如果你想在这里得到准确的话.我添加了一些便利功能,用于将机器时间转换为秒.@H_675_4@

#import <mach/mach_time.h>

double getTimeConversion(){
    double timecon;
    mach_timebase_info_data_t Tinfo;
    kern_return_t kerror;
    kerror = mach_timebase_info(&Tinfo);
    timecon = (doublE)Tinfo.numer / (doublE)Tinfo.denom;

    return  timecon;
}
double ticksToSeconds(){
    static double ticksToSeconds = 0;
    if (!ticksToSeconds) {
        ticksToSeconds = getTimeConversion() * 0.000000001;
    }
    return ticksToSeconds;
}

void processingTapCallBACk(
                 void *                          inClientData,AudioQueueProcessingTapRef      inAQTap,UInt32                          innumberFrames,Audiotimestamp *                iotimestamp,UInt32 *                        ioFlags,UInt32 *                        outnumberFrames,AudioBufferList *               ioData){

    MyObject *self = (__bridge Object *)inClientData;
    AudioQueueProcessingTapGet@R_618_9016@eAudio(inAQTap,innumberFrames,iotimestamp,ioFlags,outnumberFrames,ioData);
    if (*ioFlags ==  kAudioQueueProcessingTap_EndOfStream) {
        Float64 sampTime;
        UInt32 frameCount;
        AudioQueueProcessingTapGetQueueTime(inAQTap,&sampTime,&frameCount);
        Float64 samplesInThisCallBACk = self->frameCount - sampleTime;//file sampleCount - queue current sample
        //double secondsInCallBACk = outnumberFrames / (doublE)self->sampleRate; outnumberFrames was inaccurate
        double secondsInCallBACk = * samplesInThisCallBACk / (doublE)self->sampleRate;
        uint64_t timeOfLastSampleLeavingSpeaker = iotimestamp->mHostTime + (secondsInCallBACk / ticksToSeconds());
        [self lastSampleDoneAt:timeOfLastSampleLeavingSpeaker];
    }
}

-(void)lastSampleDoneAt:(uint64_t)lastSampTime{
    uint64_t currentTime = mach_absolute_time();
    if (lastSampTime > currentTimE) {
        double secondsFromNow = (lastSampTime - currentTimE) * ticksToSeconds();
        dispatch_after(dispatch_time(DISPATCH_TIME_Now,^{
            //do the thing!!!
        });
    }
    else{
        //do the thing!!!
    }
}

您可以在AudioQueueNewOutput之后和AudioQueueStart之前将其设置为这样.注意将桥接self传递给inClientData参数.队列实际上将self保持为void *以在回调中使用,我们将其桥接回回调中的objective-C对象.@H_675_4@

AudioStreamBasicDescription format;
AudioQueueProcessingTapRef tapRef;
UInt32 maxFrames = 0;
AudioQueueProcessingTapNew(queue,processingTapCallBACk,(__bridge void *)self,kAudioQueueProcessingTap_PostEffects,&maxFrames,&format,&tapRef);

一旦文件启动,您就可以获得最终机器时间.还有点清洁.@H_675_4@

void processingTapCallBACk(
                 void *                          inClientData,ioData);
    if (*ioFlags ==  kAudioQueueProcessingTap_StartOfStream) {

        uint64_t timeOfLastSampleLeavingSpeaker = iotimestamp->mHostTime + (self->audioDurSeconds / ticksToSeconds());
        [self lastSampleDoneAt:timeOfLastSampleLeavingSpeaker];
    }
}