核心音频：使用渲染回调传递的奇怪问题
我正在使用 RemoteIO 音频单元实现音频直通，方法是将渲染回调附加到输出总线的输入范围（即扬声器）。
一切都很顺利，......
OSStatus RenderTone(
void * inRefCon,
AudioUnitRenderActionFlags * ioActionFlags,
const AudioTimeStamp * inTimeStamp,
UInt32 inBusNumber,
UInt32 inNumberFrames,
AudioBufferList * ioData)
{
SoundEngine * soundEngine = (SoundEngine *) inRefCon;
// grab data from the MIC (ie fill up ioData)
AudioUnit thisUnit = soundEngine->remoteIOUnit->audioUnit;
OSStatus err = AudioUnitRender(thisUnit,
ioActionFlags,
inTimeStamp,
1,
inNumberFrames,
ioData);
if (result)
{
printf("Error pulling mic data");
}
assert(ioData->mNumberBuffers > 0);
// only need the first buffer
const int channel = 0;
Float32 * buff = (Float32 *) ioData->mBuffers[channel].mData;
}
直到我添加最后一行。
Float32 * buff = (Float32 *) ioData->mBuffers[channel].mData;
这条线就位后，没有错误，只是沉默。如果没有它，我可以在麦克风前点击手指并在耳机中听到它。
编辑： AudioBuffer buf0 = ioData->mBuffers[0]; // 足以导致失败
发生了什么？
这不是由编译器优化未使用的变量引起的错误。如果我设置 buff++;在下一行，行为是相同的。尽管编译器可能仍然可以检测到该变量实际上未被使用。
I am implementing an audio passthrough using the RemoteIO audio unit, by attaching a render callback to the input scope of the output bus (ie the speakers).
Everything works swimmingly, ...
OSStatus RenderTone(
void * inRefCon,
AudioUnitRenderActionFlags * ioActionFlags,
const AudioTimeStamp * inTimeStamp,
UInt32 inBusNumber,
UInt32 inNumberFrames,
AudioBufferList * ioData)
{
SoundEngine * soundEngine = (SoundEngine *) inRefCon;
// grab data from the MIC (ie fill up ioData)
AudioUnit thisUnit = soundEngine->remoteIOUnit->audioUnit;
OSStatus err = AudioUnitRender(thisUnit,
ioActionFlags,
inTimeStamp,
1,
inNumberFrames,
ioData);
if (result)
{
printf("Error pulling mic data");
}
assert(ioData->mNumberBuffers > 0);
// only need the first buffer
const int channel = 0;
Float32 * buff = (Float32 *) ioData->mBuffers[channel].mData;
}
until I add that last line.
Float32 * buff = (Float32 *) ioData->mBuffers[channel].mData;
With this line in place, no errors, simply silence. Without it, I can click my fingers in front of the microphone and hear it in my headset.
EDIT:
AudioBuffer buf0 = ioData->mBuffers[0]; // Is sufficient to cause failure
What is going on?
It is not an error caused by the compiler optimising out an unused variable. If I set buff++; on the next line, behaviour is the same. although maybe the compiler can still detect the variable is effectively unused.
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问题是第一次触发此回调时，从麦克风请求数据失败。
我应该做的是检查返回值，如果不成功则返回它（即退出回调）
可能发生的情况是我正在访问无效数据
这仍然很奇怪，但无需深入探讨它。
Problem was the request for data from the microphone was failing the very first time this callback fires.
And what I should have been doing was examining the return value, and returning it (ie quitting the callback) if it was not success
What was probably happening was that I was accessing invalid data
It is still rather bizarre, but no need to go into it.