当使用从 alSourceUnqueueBuffers() 获得的缓冲区 ID 时，alBufferData() 设置 AL_INVALID_OPERATION

Question

我正在尝试使用 OpenAL 的缓冲区队列机制从磁盘传输音频数据。我加载并排入 4 个缓冲区，开始播放源，并定期检查以刷新队列。一切看起来都很顺利，直到我第一次尝试将数据加载到从 alSourceUnqueueBuffers() 获得的回收缓冲区中。在这种情况下，alBufferData() 总是设置 AL_INVALID_OPERATION，根据the official v1.1 spec，它似乎不应该这样做。

我在 Google 和 StackOverflow 上进行了广泛搜索，但似乎找不到任何会发生这种情况的原因。我发现的最接近的事情是有人在存档的论坛帖子中使用a possibly-related issue，但细节很少，回复为空。还有this SO question，情况略有不同，但唯一答案的建议无济于事。

可能有帮助：我知道我的上下文和设备配置正确，因为将小 wav 文件完全加载到单个缓冲区并播放它们可以正常工作。通过实验，我还发现排队 2 个缓冲区，开始播放源，并立即加载和排队另外两个缓冲区不会引发错误；只有当我将处理过的缓冲区排入队列时才会遇到麻烦。

相关代码：

static constexpr int MAX_BUFFER_COUNT = 4;

#define alCall(funcCall) {funcCall; SoundyOutport::CheckError(__FILE__, __LINE__, #funcCall) ? abort() : ((void)0); }

bool SoundyOutport::CheckError(const string &pFile, int pLine, const string &pfunc)
{
    ALenum tErrCode = alGetError();
    if(tErrCode != 0)
    {
        auto tMsg = alGetString(tErrCode);
        Log::e(ro::TAG) << tMsg << " at " << pFile << "(" << pLine << "):\n"
                        << "\tAL call " << pfunc << " failed." << end;
        return true;
    }
    return false;
}

void SoundyOutport::EnqueueBuffer(const float* pData, int pFrames)
{
    static int called = 0;
    ++called;

    ALint tState;
    alCall(alGetSourcei(mSourceId, AL_SOURCE_TYPE, &tState));
    if(tState == AL_STATIC)
    {
        Stop();
//      alCall(alSourcei(mSourceId, AL_BUFFER, NULL));
    }

    ALuint tBufId = AL_NONE;
    int tQueuedBuffers = QueuedUpBuffers();
    int tReady = ProcessedBuffers();
    if(tQueuedBuffers < MAX_BUFFER_COUNT)
    {
        tBufId = mBufferIds[tQueuedBuffers];
    }
    else if(tReady > 0)
    {
        // the fifth time through, this code gets hit
        alCall(alSourceUnqueueBuffers(mSourceId, 1, &tBufId));

        // debug code: make sure these values go down by one
        tQueuedBuffers = QueuedUpBuffers();
        tReady = ProcessedBuffers();
    }
    else
    {
        return; // no update needed yet.
    }

    void* tConverted = convert(pData, pFrames);

    // the fifth time through, we get AL_INVALID_OPERATION, and call abort()
    alCall(alBufferData(tBufId, mFormat, tConverted, pFrames * mBitdepth/8, mSampleRate));

    alCall(alSourceQueueBuffers(mSourceId, 1, &mBufferId));
    if(mBitdepth == BITDEPTH_8)
    {
        delete (uint8_t*)tConverted;
    }
    else // if(mBitdepth == BITDEPTH_16)
    {
        delete (uint16_t*)tConverted;
    }
}

void SoundyOutport::PlayBufferedStream()
{
    if(!StreamingMode() || !QueuedUpBuffers())
    {
        Log::w(ro::TAG) << "Attempted to play an unbuffered stream" << end;
        return;
    }

    alCall(alSourcei(mSourceId, AL_LOOPING, AL_FALSE)); // never loop streams
    alCall(alSourcePlay(mSourceId));
}

int SoundyOutport::QueuedUpBuffers()
{
    int tCount = 0;
    alCall(alGetSourcei(mSourceId, AL_BUFFERS_QUEUED, &tCount));
    return tCount;
}

int SoundyOutport::ProcessedBuffers()
{
    int tCount = 0;
    alCall(alGetSourcei(mSourceId, AL_BUFFERS_PROCESSED, &tCount));
    return tCount;
}

void SoundyOutport::Stop()
{
    if(Playing())
    {
        alCall(alSourceStop(mSourceId));
    }

    int tBuffers;
    alCall(alGetSourcei(mSourceId, AL_BUFFERS_QUEUED, &tBuffers));
    if(tBuffers)
    {
        ALuint tDummy[tBuffers];
        alCall(alSourceUnqueueBuffers(mSourceId, tBuffers, tDummy));
    }
    alCall(alSourcei(mSourceId, AL_BUFFER, AL_NONE));
}

bool SoundyOutport::Playing()
{
    ALint tPlaying;
    alCall(alGetSourcei(mSourceId, AL_SOURCE_STATE, &tPlaying));
    return tPlaying == AL_PLAYING;
}

bool SoundyOutport::StreamingMode()
{
    ALint tState;
    alCall(alGetSourcei(mSourceId, AL_SOURCE_TYPE, &tState));
    return tState == AL_STREAMING;
}

bool SoundyOutport::StaticMode()
{
    ALint tState;
    alCall(alGetSourcei(mSourceId, AL_SOURCE_TYPE, &tState));
    return tState == AL_STATIC;
}

这是我遇到错误时在调试器中看到的带注释的屏幕截图：

我尝试了一些小的调整和变化，结果总是一样的。我已经浪费了太多天试图解决这个问题。请帮忙:)

Answer 1

当您尝试用数据填充缓冲区时会发生此错误，此时缓冲区仍在排队到源。

这个代码也是错误的。

if(tQueuedBuffers < MAX_BUFFER_COUNT)
{
    tBufId = mBufferIds[tQueuedBuffers];
}
else if(tReady > 0)
{
    // the fifth time through, this code gets hit
    alCall(alSourceUnqueueBuffers(mSourceId, 1, &tBufId));

    // debug code: make sure these values go down by one
    tQueuedBuffers = QueuedUpBuffers();
    tReady = ProcessedBuffers();
}
else
{
    return; // no update needed yet.
}

只有当缓冲区从源中取消排队时，您才能用数据填充缓冲区。但是您的第一个 if 块会获得排队到源的 tBufId。像这样重写代码

if(tReady > 0)
{
    // the fifth time through, this code gets hit
    alCall(alSourceUnqueueBuffers(mSourceId, 1, &tBufId));

    // debug code: make sure these values go down by one
    tQueuedBuffers = QueuedUpBuffers();
    tReady = ProcessedBuffers();
}
else
{
    return; // no update needed yet.
}