AudioKit：如何在 Objective-C 中使用 AKPlayer playAt 方法？

Question

我想在 iOS 应用程序中使用 Objective-C 在给定的短暂延迟后同步启动多个 AKPlayer。

我在 AudioKit 的源代码中找到了以下 swift 代码，文件 AKTiming.swift:

let bufferDuration = AKSettings.ioBufferDuration
let referenceTime = AudioKit.engine.outputNode.lastRenderTime ?? AVAudioTime.now()
let startTime = referenceTime + bufferDuration
for node in nodes {
   node.start(at: startTime)
}

如何在 objective c 中使用 NSTimeInterval 参数中的给定缓冲持续时间执行类似操作。

不幸的是，在 objective c 中不可能添加像 referenceTime + bufferDuration 和 AVAudioTime 变量，并且 now() 方法也不存在。

Apples documentation of the AVAudioTime class 很短，对我帮助不大。

我可以使用静态方法 hostTimeForSeconds 将 NSTimeInterval 转换为 hostTime，然后使用 timeWithHostTime 创建 AVAudioTime 实例吗？

感谢您的帮助！

马蒂亚斯

Answer 1

May I use the static method hostTimeForSeconds to convert NSTimeInterval to a hostTime and then timeWithHostTime to create an AVAudioTime instance?

是的！

如果您想处理 lastRenderTime 为 NULL 的情况，您还需要 #import <mach/mach_time.h> 并使用 mach_absolute_time。

double bufferDuration = AKSettings.ioBufferDuration;
AVAudioTime *referenceTime = AudioKit.engine.outputNode.lastRenderTime ?: [[AVAudioTime alloc] initWithHostTime:mach_absolute_time()];
uint64_t startHostTime = referenceTime.hostTime + [AVAudioTime hostTimeForSeconds:bufferDuration];
AVAudioTime *startTime = [[AVAudioTime alloc] initWithHostTime:startHostTime];

for (AKPlayer *node in nodes) {
    [node startAt:startTime];
}

Answer 2

Unfortunately an addition like referenceTime + bufferDuration with AVAudioTime variable is not possible in objective c, and a now() method also doesn't exist.

它们不存在，因为它不是 AVAudioTime 的一部分，它是 AudioKit 的扩展。

如果您查看他们的 source code，您会发现：

// An AVAudioTime with a valid hostTime representing now.
public static func now() -> AVAudioTime {
    return AVAudioTime(hostTime: mach_absolute_time())
}

/// Returns an AVAudioTime offset by seconds.
open func offset(seconds: Double) -> AVAudioTime {

    if isSampleTimeValid && isHostTimeValid {
        return AVAudioTime(hostTime: hostTime + seconds / ticksToSeconds,
                           sampleTime: sampleTime + AVAudioFramePosition(seconds * sampleRate),
                           atRate: sampleRate)
    } else if isHostTimeValid {
        return AVAudioTime(hostTime: hostTime + seconds / ticksToSeconds)
    } else if isSampleTimeValid {
        return AVAudioTime(sampleTime: sampleTime + AVAudioFramePosition(seconds * sampleRate),
                           atRate: sampleRate)
    }
    return self
}

public func + (left: AVAudioTime, right: Double) -> AVAudioTime {
    return left.offset(seconds: right)
}

您也可以自己实现这些扩展。我不认为你可以在 Objective C 中实现 + 运算符，所以你只需要使用偏移方法。（注意：我没有检查以下内容）

double ticksToSeconds() {
    struct mach_timebase_info tinfo;
    kern_return_t err = mach_timebase_info(&tinfo);
    double timecon = (double)(tinfo.numer) / (double)(tinfo.denom);
    return timecon * 0.000000001;
}

@interface AVAudioTime (Extensions)

+ (AVAudioTime *)now;
- (AVAudioTime *)offsetWithSeconds:(double)seconds;

@end

@implementation AVAudioTime (Extensions)

+ (AVAudioTime *)now {
    return [[AVAudioTime alloc] initWithHostTime:mach_absolute_time()];
}

- (AVAudioTime *)offsetWithSeconds:(double)seconds {
    if ([self isSampleTimeValid] && [self isHostTimeValid]) {
        return [[AVAudioTime alloc] initWithHostTime:self.hostTime + (seconds / ticksToSeconds())
                                          sampleTime:self.sampleTime + (seconds * self.sampleRate)
                                              atRate:self.sampleRate];
    }
    else if ([self isHostTimeValid]) {
        return [[AVAudioTime alloc] initWithHostTime:self.hostTime + (seconds / ticksToSeconds())];
    }
    else if ([self isSampleTimeValid]) {
        return [[AVAudioTime alloc] initWithSampleTime:self.sampleTime + (seconds * self.sampleRate)
                                                atRate:self.sampleRate];
    }
    return self;
}

@end

AudioKit：如何在 Objective-C 中使用 AKPlayer playAt 方法？

AudioKit: How to use AKPlayer playAt method in Objective-C?

objective-c

audiokit