与CAPlayThrough示例问题 [英] Issues with CAPlayThrough Example

问题描述

我想了解X $ C $ç核心音频和偶然发现了这个例子：

I am trying to learn Xcode Core Audio and stumbled upon this example:

<一个href=\"https://developer.apple.com/library/mac/sample$c$c/CAPlayThrough/Introduction/Intro.html#//apple_ref/doc/uid/DTS10004443\" rel=\"nofollow\">https://developer.apple.com/library/mac/sample$c$c/CAPlayThrough/Introduction/Intro.html#//apple_ref/doc/uid/DTS10004443

我的目的是捕捉到的原始音频。每次我打了一个破发点，我失去了音讯。由于它使用 CARingBuffer 。

My intention is to capture the raw audio. Everytime I hit a break point, I lose the audio. Since it is using CARingBuffer.

1. 您会如何排除时间factor.I不需要实时音频。


2. 由于它使用 CARingBuffer 应该继续写同一个内存位置？那么，为什么不听我的声音？如果我有一个断点？

1. How would you remove the time factor.I don't need real-time audio.
2. Since it is using CARingBuffer it should keep on writing to same memory location? So why don't I hear the audio? If I have a breakpoint?

我读的学习核心音频的书。但是，到目前为止，我无法弄清楚以下code的这一部分：

I am reading the Learning Core Audio book. But, so far I cannot figure out this part of the following code:

CARingBufferError CARingBuffer::Store(const AudioBufferList *abl, UInt32 framesToWrite, SampleTime startWrite)
{
    if (framesToWrite == 0)
        return kCARingBufferError_OK;

    if (framesToWrite > mCapacityFrames)
        return kCARingBufferError_TooMuch;      // too big!

    SampleTime endWrite = startWrite + framesToWrite;

    if (startWrite < EndTime()) {
        // going backwards, throw everything out
        SetTimeBounds(startWrite, startWrite);
    } else if (endWrite - StartTime() <= mCapacityFrames) {
        // the buffer has not yet wrapped and will not need to
    } else {
        // advance the start time past the region we are about to overwrite
        SampleTime newStart = endWrite - mCapacityFrames;   // one buffer of time behind where we're writing
        SampleTime newEnd = std::max(newStart, EndTime());
        SetTimeBounds(newStart, newEnd);
    }

    // write the new frames
    Byte **buffers = mBuffers;
    int nchannels = mNumberChannels;
    int offset0, offset1, nbytes;
    SampleTime curEnd = EndTime();

    if (startWrite > curEnd) {
        // we are skipping some samples, so zero the range we are skipping
        offset0 = FrameOffset(curEnd);
        offset1 = FrameOffset(startWrite);
        if (offset0 < offset1)
            ZeroRange(buffers, nchannels, offset0, offset1 - offset0);
        else {
            ZeroRange(buffers, nchannels, offset0, mCapacityBytes - offset0);
            ZeroRange(buffers, nchannels, 0, offset1);
        }
        offset0 = offset1;
    } else {
        offset0 = FrameOffset(startWrite);
    }

    offset1 = FrameOffset(endWrite);
    if (offset0 < offset1)
        StoreABL(buffers, offset0, abl, 0, offset1 - offset0);
    else {
        nbytes = mCapacityBytes - offset0;
        StoreABL(buffers, offset0, abl, 0, nbytes);
        StoreABL(buffers, 0, abl, nbytes, offset1);
    }

    // now update the end time
    SetTimeBounds(StartTime(), endWrite);

    return kCARingBufferError_OK;   // success
}

谢谢！

推荐答案

如果我的理解这个问题很好，信号同时输入单元（制片人）在断点处暂停正在丧失。我presume这可能是预期的行为。 CoreAudio的是一个 拉模型的引擎实时线程运行。这意味着，在某些情况下，你的制作人遇到断点，环形缓冲区清空，输出单元（消费者）继续运行，但会从缓冲什么，而通关链中断，因此可能的沉默。

If I understood the question well, the signal is lost while input unit (producer) being halted on a breakpoint. I presume this may be the expected behavior. CoreAudio is a pull-model engine running of the real time thread. This means under some conditions your producer hits a breakpoint, the ring buffer empties, the output unit (consumer) keeps on running, but gets nothing from the buffer while the playthrough chain is interrupted, hence the possible silence.

也许从这个例子code是不是真的最简单的一个：我看这也归零，如果环形缓冲区溢出得到缓冲的音频/欠载，AFAICT。
在这个问题的长期的原始音频的也是不言自明的，我不知道是什么意思。我建议想学异步I / O使用简单的循环缓冲区。有几个人（无强制性时间值）在GitHub上。

Perhaps this code from the example is not really the simplest one: I see it also zeroes audio buffers if ring buffer gets overrun/underrun, AFAICT. The term "raw audio" in the question is also not self-explanatory, I'm not sure what does it mean. I would suggest trying to learn async i/o using simpler circular buffers. There are few of them (without obligatory time values) on GitHub.

请还这么好心来格式化源$ C ​​$ C，方便阅读。

Please also be so kind to format the source code for easier reading.

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