OpenAL 流式播放音频的时候结尾有杂音。

[Xpol Wan]

大家好，

在OpenAL list里面问没有人搭理，只好来这里求助。

我在做一个简单的游戏引擎，音频部分的PC实现采用的是OpenAL。

但是我发现流式播放音频的时候，结尾会有杂音。具体的说就是播放完毕后

还会播放该音频的某段声音，持续很短。就像是alSourceStop没有真正刹住车

一样。

我的环境是Windows7。有和其他游戏引擎Love2D比较过。Love2D却没有这个现象。

我开始猜想是不是我用的是单线程的原因。经过改成一个解码一个播放线程后情况依旧。

我也有试过OpenAL 1.1 SDK [1] 里面带的sample中的playstream例子(见后面的代码)。

情况是一样的，结尾还是有杂音。

由于刚刚开始接触较底层的音频编程也是刚刚开始使用OpenAL，所以请各位有经验的帮忙指点一下。

[1] OpenAL 1.1 SDK: http://connect.creativelabs.com/openal/Downloads/OpenAL11CoreSDK.zip

SDK中的 PlayStream.cpp：

#include "Framework.h"

#include "CWaves.h"

#define NUMBUFFERS              (4)

#define SERVICE_UPDATE_PERIOD (20)

#define TEST_WAVE_FILE "stereo.wav"

int main()

{

ALuint     uiBuffers[NUMBUFFERS];

ALuint     uiSource;

ALuint uiBuffer;

ALint iState;

CWaves * pWaveLoader = NULL;

WAVEID WaveID;

ALint iLoop;

ALint iBuffersProcessed, iTotalBuffersProcessed, iQueuedBuffers;

WAVEFORMATEX wfex;

unsigned long ulDataSize = 0;

unsigned long ulFrequency = 0;

unsigned long ulFormat = 0;

unsigned long ulBufferSize;

unsigned long ulBytesWritten;

void * pData = NULL;

// Initialize Framework

ALFWInit();

ALFWprintf("PlayStream Test Application\n");

if (!ALFWInitOpenAL())

{

ALFWprintf("Failed to initialize OpenAL\n");

ALFWShutdown();

return 0;

}

    // Generate some AL Buffers for streaming

alGenBuffers( NUMBUFFERS, uiBuffers );

// Generate a Source to playback the Buffers

    alGenSources( 1, &uiSource );

// Create instance of WaveLoader class

pWaveLoader = new CWaves();

if ((pWaveLoader) && (SUCCEEDED(pWaveLoader->OpenWaveFile(ALFWaddMediaPath(TEST_WAVE_FILE), &WaveID))))

{

pWaveLoader->GetWaveSize(WaveID, &ulDataSize);

pWaveLoader->GetWaveFrequency(WaveID, &ulFrequency);

pWaveLoader->GetWaveALBufferFormat(WaveID, &alGetEnumValue, &ulFormat);

// Queue 250ms of audio data

pWaveLoader->GetWaveFormatExHeader(WaveID, &wfex);

ulBufferSize = wfex.nAvgBytesPerSec >> 2;

// IMPORTANT : The Buffer Size must be an exact multiple of the BlockAlignment ...

ulBufferSize -= (ulBufferSize % wfex.nBlockAlign);

if (ulFormat != 0)

{

pData = malloc(ulBufferSize);

if (pData)

{

// Set read position to start of audio data

pWaveLoader->SetWaveDataOffset(WaveID, 0);

// Fill all the Buffers with audio data from the wavefile

for (iLoop = 0; iLoop < 4; iLoop++)

{

if (SUCCEEDED(pWaveLoader->ReadWaveData(WaveID, pData, ulBufferSize, &ulBytesWritten)))

{

alBufferData(uiBuffers[iLoop], ulFormat, pData, ulBytesWritten, ulFrequency);

alSourceQueueBuffers(uiSource, 1, &uiBuffers[iLoop]);

}

}

// Start playing source

alSourcePlay(uiSource);

iTotalBuffersProcessed = 0;

while (!ALFWKeyPress())

{

Sleep( SERVICE_UPDATE_PERIOD );

// Request the number of OpenAL Buffers have been processed (played) on the Source

iBuffersProcessed = 0;

alGetSourcei(uiSource, AL_BUFFERS_PROCESSED, &iBuffersProcessed);

// Keep a running count of number of buffers processed (for logging purposes only)

iTotalBuffersProcessed += iBuffersProcessed;

ALFWprintf("Buffers Processed %d\r", iTotalBuffersProcessed);

// For each processed buffer, remove it from the Source Queue, read next chunk of audio

// data from disk, fill buffer with new data, and add it to the Source Queue

while (iBuffersProcessed)

{

// Remove the Buffer from the Queue.  (uiBuffer contains the Buffer ID for the unqueued Buffer)

uiBuffer = 0;

alSourceUnqueueBuffers(uiSource, 1, &uiBuffer);

// Read more audio data (if there is any)

pWaveLoader->ReadWaveData(WaveID, pData, ulBufferSize, &ulBytesWritten);

if (ulBytesWritten)

{

// Copy audio data to Buffer

alBufferData(uiBuffer, ulFormat, pData, ulBytesWritten, ulFrequency);

// Queue Buffer on the Source

alSourceQueueBuffers(uiSource, 1, &uiBuffer);

}

iBuffersProcessed--;

}

// Check the status of the Source.  If it is not playing, then playback was completed,

// or the Source was starved of audio data, and needs to be restarted.

alGetSourcei(uiSource, AL_SOURCE_STATE, &iState);

if (iState != AL_PLAYING)

{

// If there are Buffers in the Source Queue then the Source was starved of audio

// data, so needs to be restarted (because there is more audio data to play)

alGetSourcei(uiSource, AL_BUFFERS_QUEUED, &iQueuedBuffers);

if (iQueuedBuffers)

{

alSourcePlay(uiSource);

}

else

{

// Finished playing

break;

}

}

}

// Stop the Source and clear the Queue

alSourceStop(uiSource);

alSourcei(uiSource, AL_BUFFER, 0);

// Release temporary storage

free(pData);

pData = NULL;

}

else

{

ALFWprintf("Out of memory\n");

}

}

else

{

ALFWprintf("Unknown Audio Buffer format\n");

}

// Close Wave Handle

pWaveLoader->DeleteWaveFile(WaveID);

}

else

{

ALFWprintf("Failed to load %s\n", ALFWaddMediaPath(TEST_WAVE_FILE));

}

    // Clean up buffers and sources

alDeleteSources( 1, &uiSource );

alDeleteBuffers( NUMBUFFERS, uiBuffers );

if (pWaveLoader)

delete pWaveLoader;

ALFWShutdownOpenAL();

ALFWShutdown();

    return 0;

}