循环流式传输 .ogg 音频 - OpenAL

Question

我有问题循环播放一个流式的 Ogg Vorbis 文件。

这是代码：

fslStream_OGG::fslStream_OGG()
{
 className = "fslSound";
 iMemSize = 0;
 iLength = 0;
 bSourceRelative = false;
 bIsLooping = false;
 bForceStop = false;
 bActive = false;
 source = buffer = 0;
 current_gain = 1.0f;
 outer_gain = 0;
 snd_info.uiChannels = snd_info.uiFrequency = snd_info.uiSampling = 0;
}

fslStream_OGG::~fslStream_OGG()
{
 if (bStreamCreated)
 {
  alSourceStop(source);
  Empty();
  alDeleteSources(1,&source);
  alDeleteBuffers(2,buffers);
  ov_clear(&oggStream);
 }
}

bool fslStream_OGG::Update()
{
 ALenum state; 
 alGetSourcei(source,AL_SOURCE_STATE,&state);

 if (state == AL_PAUSED || !bActive) return false;

 int processed;
    alGetSourcei(source,AL_BUFFERS_PROCESSED,&processed);

    while (processed--)
    {
        ALuint bufferI;
        alSourceUnqueueBuffers(source,1,&bufferI);
        Stream(bufferI);
  if (bActive) alSourceQueueBuffers(source,1,&bufferI);
    }

 if (state == AL_STOPPED || !bActive)
 {
  bActive = false;
  StreamSetPos(0.0f);
  if (bForceStop) return false;

  if (bIsLooping)
  {
   alSourceStop(source); // <- *** note these ***
   Empty();    // <- *** 2 lines of code ***
   StreamPlay();
   alSourcePlay(source);
  }
  else
  {
   return true;
  }
 }

 return false;
}

void fslStream_OGG::StreamPlay()
{
 if (!bActive)
 {
  bActive = true;
  bForceStop = false;
  Stream(buffers[0]);
  Stream(buffers[1]);

  alSourceQueueBuffers(source,2,buffers);
 }
}

bool fslStream_OGG::Open(const char* strFile)
{
 bStreamCreated = false;
 vorbis_info* vorbisInfo;
 oggFile = fopen(strFile,"rb");

 if (!oggFile) return false;

 if (ov_open_callbacks(oggFile,&oggStream,NULL,0,OV_CALLBACKS_DEFAULT) != 0)
 {
  fclose(oggFile);
  return false;
 }

 vorbisInfo = ov_info(&oggStream,-1);

 if (vorbisInfo->channels == 1)
  format = AL_FORMAT_MONO16;
 else format = AL_FORMAT_STEREO16;

 alGenBuffers(2,buffers);
 alGenSources(1,&source);

 iLength = (long)(ov_time_total(&oggStream,-1) * 1000.0);
 snd_info.uiChannels = (format == AL_FORMAT_MONO8 || format == AL_FORMAT_MONO16)? 1:2;
 snd_info.uiSampling = (format == AL_FORMAT_MONO8 || format == AL_FORMAT_STEREO8)? 8:16;
 snd_info.uiFrequency = vorbisInfo->rate;

 bStreamCreated = true;
 bIsStream = true;

 return true;
}

void fslStream_OGG::Stream(ALuint bufferI)
{
 int  size = 0;
 int  section;
 int  result;

 bActive = true;

 while (size < OGG_STREAM_BUFFER_SIZE)
 {
  result = ov_read(&oggStream,data + size,OGG_STREAM_BUFFER_SIZE - size,0,2,1,&section);

  if (result > 0)
  {
   size += result;
  }
  else
  {
   if (result < 0) return; else break;
  }
 }

 if (size == 0) { bActive = false; return; }

    alBufferData(bufferI,format,data,size,snd_info.uiFrequency);
}

void fslStream_OGG::Empty()
{
 int queued;
 alGetSourcei(source,AL_BUFFERS_QUEUED,&queued);

 while (queued--)
 {
        ALuint bufferI;
  alSourceUnqueueBuffers(source,1,&bufferI);
 }
}

void fslStream_OGG::StreamSetPos(float p)
{
 ov_time_seek(&oggStream,p);
}

float fslStream_OGG::StreamGetPos()
{
 return (float)ov_time_tell(&oggStream);
}

请注意我标记为***的两行代码。

在所有情况下，文件开始播放时很好，结束时会倒回。但是：

如果没有那2行代码，则重复播放时声音会“损坏”。如果再次重复播放，声音会更加“损坏”。我认为这是因为当流重复时，OpenAl和Vorbis解码器在写入/读取缓冲区时变得“不同步”。

如果我添加了那2行代码，则文件会在不出现损坏的情况下重复播放。然而，文件不会无缝地重复播放; 它会在结束前倒回几个十分之一秒。我怀疑这是因为在返回开始之前未完全播放缓冲区。

如果有人能伸出援手，我将不胜感激。

谢谢！

- Bill Kotsias

Answer 1

看起来我已经解决了这个问题（没有详细测试，无法确定）。

我已经按照以下方式修复了更新方法：

bool fslStream_OGG::Update()
{
    ALenum state; 
    alGetSourcei(source,AL_SOURCE_STATE,&state);

    //if (state == AL_PAUSED || !bActive) return false; // <- WRONG
    if (state == AL_PAUSED) return false;

    int processed;
    alGetSourcei(source,AL_BUFFERS_PROCESSED,&processed);

    while (processed--)
    {
        ALuint bufferI;
        alSourceUnqueueBuffers(source,1,&bufferI);
        Stream(bufferI);
        if (bActive) alSourceQueueBuffers(source,1,&bufferI);
    }

    //if (state == AL_STOPPED || !bActive) /// <- WRONG
    if (state == AL_STOPPED)
    {
        bActive = false;
        StreamSetPos(0.0f);
        if (bForceStop) return false;

        if (bIsLooping)
        {
            //alSourceStop(source); // <- I have added these
            //Empty();              // <- 2 lines of code
            StreamPlay();
            alSourcePlay(source);
        }
        else
        {
            return true;
        }
    }

    return false;
}

这两行代码现在似乎不是必要的。将需要在不同的操作系统、硬件等进行测试...

- Bill Kotsias

---

嘿，老兄，我遇到了一个非常类似于你的问题（使用非常相似的Update函数;看起来我们读了同一篇教程）。你用这个解决方案怎么样了？我的循环问题与你的相同。在重新启动流之前，它会向后跳几毫秒。但是即使没有循环，它也会这样做。当它到达音频文件的末尾时，在停止之前会重新播放声音的最后几毫秒。这是一个令人恼火的微小抖动。你用这个解决方案怎么样了？ - Anthony

这里有一个教程，逐行介绍了所有必要的代码。https://indiegamedev.net/2020/01/16/how-to-stream-ogg-files-with-openal-in-c/ - NeomerArcana