iphone - 使用 AudioQueue 服务播放 MP3 数据缓冲区 : Prime failed (-50)

Question

这几天我一直在努力寻找在 iPhone 上使用 AudioQueue 服务播放网络音频流(MP3 数据包格式)的方法。

为了成功实现这个目标，我先用AudioQueue把普通的本地MP3文件拿来播放，果然可以。然后，我用 stdio 函数 fread 替换了 AudioFileReadPackets，每次我都像 AudioFileReadPackets 一样 fread 相同数量的 mp3 数据包，以模拟来自网络的音频流。然而，这一次，错误来了:

2011-09-28 14:21:28.245 SunFlower[1554:207] Prime: Exiting because mConverterError is -50 (0x11940 req, 0x0 primed)
2011-09-28 14:21:28.253 SunFlower[1554:207] Prime failed (-50); will stop (72000/0 frames)

有人知道这个“Prime failed (-50)”错误的原因吗？帮忙zzzzzzz

*********************************************** ****************************************************** ****************************************************** *********************。

为了解释我在替换工作上做了什么，我想向您展示代码的主要更改部分，有两部分:“替换前”和“替换后”

1. 替换前(播放本地 MP3 文件):

1) 音频队列runloop回调

static void HandleOutputBuffer(void                *aqData, 
                               AudioQueueRef       inAQ, 
                               AudioQueueBufferRef inBuffer) 
{
    AQPlayerState *pAqData = (AQPlayerState *) aqData; 
    UInt32 numBytesReadFromFile;
    UInt32 numPackets = pAqData->mNumPacketsToRead;
    UInt32 i = 0;

    printf("HandleOutputBuffer::Start!\n");
    //If the audio queue is stopped, returns immediately
    if(pAqData->mIsRunning == 0) 
    {
        printf("HandleOutputBuffer::Error Return!\n");
        return;
    }

    //Read a packet of audio data from file stream
    AudioFileReadPackets(pAqData->mAudioFile,
                         false,
                         &numBytesReadFromFile,
                         pAqData->mPacketDescs,
                         pAqData->mCurrentPacket,
                         &numPackets,
                         inBuffer->mAudioData);

    //Enqueue the audio packet into the audio queue
    if(numPackets > 0) 
    {
        printf("HandleOutputBuffer::Step 1!\n");
        inBuffer->mAudioDataByteSize = numBytesReadFromFile;
        AudioQueueEnqueueBuffer(pAqData->mQueue,
                                inBuffer,
                                (pAqData->mPacketDescs ? numPackets : 0),
                                pAqData->mPacketDescs);

        pAqData->mCurrentPacket += numPackets;
    }
    else
    {
        printf("HandleOutputBuffer::Step 2!\n");
        AudioQueueStop(pAqData->mQueue,
                       false);
        pAqData->mIsRunning = false;
    }
}

2) 打开音频文件

OSStatus AqOpenAudioFile(char *filePath, AQPlayerState *pAqData)
{
    CFURLRef audioFileURL;
    OSStatus result;
    UInt32 maxPacketSize;
    UInt32 propertySize = sizeof (maxPacketSize);

    audioFileURL = 
        CFURLCreateFromFileSystemRepresentation(NULL,
                                                (const UInt8 *) filePath,
                                                strlen (filePath),
                                                false);

    result = AudioFileOpenURL(audioFileURL,
                              kAudioFileReadPermission,
                              0,
                              &(pAqData->mAudioFile));
    CFRelease(audioFileURL);

    AudioFileGetProperty(pAqData->mAudioFile,
                         kAudioFilePropertyPacketSizeUpperBound,
                         &propertySize,
                         &maxPacketSize);

    DeriveBufferSize(pAqData->mDataFormat,
                     maxPacketSize,
                     0.5,
                     &(pAqData->bufferByteSize),
                     &(pAqData->mNumPacketsToRead));

    return result;
}

3) 创建音频队列

OSStatus AqCreateAudioQueue(AQPlayerState *pAqData)
{
    UInt32 dataFormatSize = sizeof (AudioStreamBasicDescription);
    OSStatus result;
    bool isFormatVBR;
    UInt32 cookieSize = sizeof (UInt32);
    bool couldNotGetProperty;

    AudioFileGetProperty(pAqData->mAudioFile,
                         kAudioFilePropertyDataFormat,
                         &dataFormatSize,
                         &(pAqData->mDataFormat));

    result = AudioQueueNewOutput(&(pAqData->mDataFormat),
                                 HandleOutputBuffer,
                                 pAqData,
                                 CFRunLoopGetCurrent(),
                                 kCFRunLoopCommonModes,
                                 0,
                                 &(pAqData->mQueue));

    //Configurate the VBR property if any
    isFormatVBR = (pAqData->mDataFormat.mBytesPerPacket == 0 || 
                   pAqData->mDataFormat.mFramesPerPacket == 0);

    if(isFormatVBR)
    {
        pAqData->mPacketDescs = 
            (AudioStreamPacketDescription*)malloc(pAqData->mNumPacketsToRead * sizeof(AudioStreamPacketDescription));
    }
    else
    {
        pAqData->mPacketDescs = NULL;
    }

    //Set Metadata for Audio Queue
    couldNotGetProperty = 
        AudioFileGetPropertyInfo(pAqData->mAudioFile,
                                 kAudioFilePropertyMagicCookieData,
                                 &cookieSize,
                                 NULL);

    if (!couldNotGetProperty && cookieSize)
    {
        char* magicCookie = (char *)malloc(cookieSize);
        AudioFileGetProperty(pAqData->mAudioFile,
                             kAudioFilePropertyMagicCookieData,
                             &cookieSize,
                             magicCookie);

        AudioQueueSetProperty(pAqData->mQueue,
                              kAudioQueueProperty_MagicCookie,
                              magicCookie,
                              cookieSize);
        free(magicCookie);
    }

    //Set the playback gain
    AudioQueueSetParameter(pAqData->mQueue,
                           kAudioQueueParam_Volume,
                           AQ_PLAYBACK_GAIN);    
}

2。替换后(通过fread获取playbak mp3 data buffer):

为了代码移植顺利，我复制了关键变量的运行时值，如pAqData->bufferByteSize、pAqData->mNumPacketsToRead、pAqData->mDataFormat…等。并在替换代码中使用复制的值直接初始化这些变量。此行为的目的是放弃涉及 AudioToolbox 框架的接口(interface)，如:AudioFileOpenURL、AudioFileGetProperty、AudioFileReadPackets……然后，我们可以使用 stdio 函数 fread 直接获取 mp3 数据包。修改后的代码如下所示:

1)音频队列runloop回调(之前的代码中，AudioFileReadPackets读取了338个包，共129792字节，我直接将这些值复制到替换代码中)

static void HandleOutputBuffer(void                *aqData, 
                               AudioQueueRef       inAQ, 
                               AudioQueueBufferRef inBuffer) 
{
    AQPlayerState *pAqData = (AQPlayerState *) aqData; 
    UInt32 numBytesReadFromFile;
    UInt32 numPackets = pAqData->mNumPacketsToRead;
    UInt32 i = 0;

    printf("HandleOutputBuffer::Start!\n");
    //If the audio queue is stopped, returns immediately
    if(pAqData->mIsRunning == 0) 
    {
        printf("HandleOutputBuffer::Error Return!\n");
        return;
    }

    //Read a packet of audio data using fread
    memset(audio_buffer, 0, 327680);
    memset(inBuffer->mAudioData, 0, 327680);
    pAqData->mPacketDescs->mStartOffset = 0;
    pAqData->mPacketDescs->mVariableFramesInPacket = 0;
    pAqData->mPacketDescs->mDataByteSize = 384;

    numBytesReadFromFile = fread(audio_buffer, sizeof(uint8_t), 129792, source_file);
    numPackets = 338;
    memcpy(inBuffer->mAudioData, audio_buffer, 327680);

    //Enqueue the audio packet into the audio queue
    if(numPackets > 0) 
    {
        printf("HandleOutputBuffer::Step 1!\n");
        inBuffer->mAudioDataByteSize = numBytesReadFromFile;
        AudioQueueEnqueueBuffer(pAqData->mQueue,
                                inBuffer,
                                (pAqData->mPacketDescs ? numPackets : 0),
                                pAqData->mPacketDescs);

        pAqData->mCurrentPacket += numPackets;
    }
    else
    {
        printf("HandleOutputBuffer::Step 2!\n");
        AudioQueueStop(pAqData->mQueue,
                       false);
        pAqData->mIsRunning = false;
    }
}

2) 打开音频文件(用fopen代替AudioFileOpenURL)

OSStatus AqOpenAudioFile(char *filePath, AQPlayerState *pAqData)
{
    CFURLRef audioFileURL;
    OSStatus result;
    UInt32 maxPacketSize;
    UInt32 propertySize = sizeof (maxPacketSize);

    source_file = fopen(filePath, "r");

    memset(audio_buffer, 0, 327680);
    fread(audio_buffer, sizeof(uint8_t), 32, source_file);

    pAqData->bufferByteSize = 327680;
    pAqData->mNumPacketsToRead = 338;

    return result;
}

3)创建音频队列(直接初始化pAqData->mDataFormat为本地MP3播放模式赋值)

OSStatus AqCreateAudioQueue(AQPlayerState *pAqData)
{
    UInt32 dataFormatSize = sizeof (AudioStreamBasicDescription);
    OSStatus result;
    bool isFormatVBR;
    UInt32 cookieSize = sizeof (UInt32);
    bool couldNotGetProperty;


    memset(&(pAqData->mDataFormat), 0, sizeof(AudioStreamBasicDescription));
    pAqData->mDataFormat.mSampleRate = 48000;
    pAqData->mDataFormat.mFormatID = 778924083;//mp3 ID
    pAqData->mDataFormat.mFramesPerPacket = 1152;
    pAqData->mDataFormat.mChannelsPerFrame = 2;


    result = AudioQueueNewOutput(&(pAqData->mDataFormat),
                                 HandleOutputBuffer,
                                 pAqData,
                                 CFRunLoopGetCurrent(),
                                 kCFRunLoopCommonModes,
                                 0,
                                 &(pAqData->mQueue));

    //Configurate the VBR property if any
    isFormatVBR = (pAqData->mDataFormat.mBytesPerPacket == 0 || 
                   pAqData->mDataFormat.mFramesPerPacket == 0);

    if(isFormatVBR)
    {
        pAqData->mPacketDescs = 
            (AudioStreamPacketDescription*)malloc(pAqData->mNumPacketsToRead * 
                                              sizeof(AudioStreamPacketDescription));
    }
    else
    {
        pAqData->mPacketDescs = NULL;
    }

    //Set the playback gain
    AudioQueueSetParameter(pAqData->mQueue,
                           kAudioQueueParam_Volume,
                           AQ_PLAYBACK_GAIN);    
}

Answer 1

伙计们:

我找到了根本原因!

问题出在函数HandleOutputBuffer(改的)!

因为函数fread每次都要读取338包mp3数据(不是1包)，所以[pAqData->mPacketDescs]不是一个单一的变量，它实际上是一个数组，大小为338个数组项。因此，我们必须初始化所有 338 个数组项。

因此，我们需要更改代码:

static void HandleOutputBuffer(void                *aqData, 
                               AudioQueueRef       inAQ, 
                               AudioQueueBufferRef inBuffer) 
{
    ...
    pAqData->mPacketDescs->mStartOffset = 0;
    pAqData->mPacketDescs->mVariableFramesInPacket = 0;
    pAqData->mPacketDescs->mDataByteSize = 384;
    ...
}

进入

static void HandleOutputBuffer(void                *aqData, 
                               AudioQueueRef       inAQ, 
                               AudioQueueBufferRef inBuffer) 
{
    ...
    for (i = 0; i < 338; i++) 
    {
        pAqData->mPacketDescs[i].mStartOffset = PACKET_SIZE * i;
        pAqData->mPacketDescs[i].mVariableFramesInPacket = 0;
        pAqData->mPacketDescs[i].mDataByteSize = PACKET_SIZE;
    }
    ...
}

终于，问题解决了!