objective-c - 音频文件播放无音量

Question

我使用Apple Audio Queue Services指南制作了一个命令行类型的应用程序，以从磁盘播放文件

#import <Foundation/Foundation.h>
#import <AudioToolbox/AudioToolbox.h>
#define kNumberBuffers 3        // the number of audio queue buffers to use

//An AudioStreamBasicDescription structure (from CoreAudioTypes.h) representing the audio data format of the file being played. This format gets used by the audio queue specified in the mQueue field.

typedef struct AQPlayerState{
    AudioStreamBasicDescription     mDataFormat;
    AudioQueueRef                   mQueue; //The playback audio queue created by your application.
    AudioQueueBufferRef             mBuffers[kNumberBuffers]; //An array holding pointers to the audio queue buffers managed by the audio queue.
    AudioFileID                     mAudioFile; //An audio file object that represents the audio file your program plays.
    UInt32                          bufferByteSize; //The size, in bytes, for each audio queue buffer.
    SInt64                          mCurrentPacket;//The packet index for the next packet to play from the audio file.
    UInt32                          mNumPacketsToRead; //The number of packets to read on each invocation of the audio queue’s playback callback
    AudioStreamPacketDescription    *mPacketDecs; //For VBR audio data, the array of packet descriptions for the file being played. For CBR data, the value is NULL.
    BOOL                            isRunning;
}AQPlayerState;

static void HandleOutputBuffer(
                               void                 *AQData,
                               AudioQueueRef        inAQ,
                               AudioQueueBufferRef  inBuffer
                               ){
    OSStatus error;
    AQPlayerState *pAQData=(AQPlayerState*)AQData;
    if(!pAQData->isRunning)return;
    UInt32 numBytesReadFromFile;   // A variable to hold the number of bytes of audio data read from the file being played.

    UInt32 numPackets=pAQData->mNumPacketsToRead;  // Initializes the numPackets variable with the number of packets to read from the file being played.
    error=AudioFileReadPacketData(pAQData->mAudioFile,
                                  false,
                                  &numBytesReadFromFile,
                                  pAQData->mPacketDecs,
                                  pAQData->mCurrentPacket,
                                  &numPackets,
                                  inBuffer->mAudioData
                                );
    assert(error==noErr);
  //  Tests whether some audio data was retrieved from the file. If so, enqueues the newly-filled buffer. If not, stops the audio queue.
    if(numPackets > 0){
        inBuffer->mAudioDataByteSize=numBytesReadFromFile;  //Tells the audio queue buffer structure the number of bytes of data that were read.

        error=AudioQueueEnqueueBuffer(pAQData->mQueue,inBuffer,
                                  (pAQData->mPacketDecs ? numPackets : 0),
                                  pAQData->mPacketDecs);
        pAQData->mCurrentPacket+=numPackets;    //Increments the packet index according to the number of packets that were read.
    }else{
        AudioQueueStop(pAQData->mQueue,0);
        pAQData->isRunning=0;
    }


}
void DeriveBufferSize(
                      AudioStreamBasicDescription *ASBDesc,
                      UInt32                      maxPacketSize,
                      Float64                     seconds,
                      UInt32                      *outBufSize,
                      UInt32                      *outNumPacketsToRead
                      ){
    static const int maxBufSize=0x50000;
    static const int minBufSize=0x4000;

    if(ASBDesc->mFramesPerPacket!=0){
        Float64 numPacketsForTime=
        ASBDesc->mSampleRate/ASBDesc->mFramesPerPacket * seconds;
        *outBufSize=numPacketsForTime *maxPacketSize;
    }else{
        *outBufSize=maxBufSize > maxPacketSize ? maxBufSize : maxPacketSize;
    }
    if (                                                             // 10
        *outBufSize > maxBufSize &&
        *outBufSize > maxPacketSize
        )
        *outBufSize = maxBufSize;
    else {                                                           // 11
        if (*outBufSize < minBufSize)
            *outBufSize = minBufSize;
    }
    *outNumPacketsToRead = *outBufSize / maxPacketSize;           // 12

}
int main(int argc, const char * argv[]) {
    AQPlayerState AQPlayer;
    CFURLRef audioFileURL=CFURLCreateFromFileSystemRepresentation(NULL,
                                                                  (const UInt8*)argv[1], strlen(argv[1]),0);
    OSStatus result;
    result=AudioFileOpenURL(audioFileURL,fsRdPerm, 0,&AQPlayer.mAudioFile);
    UInt32 dataFormatSize=sizeof(AQPlayer.mDataFormat);
    AudioFileGetProperty(AQPlayer.mAudioFile,kAudioFilePropertyDataFormat,&dataFormatSize,&AQPlayer.mDataFormat);
    // Create playback queue
    AudioQueueNewOutput(&AQPlayer.mDataFormat,
                        HandleOutputBuffer,
                        &AQPlayer,
                        CFRunLoopGetCurrent(),
                        kCFRunLoopCommonModes,
                        0,
                        &AQPlayer.mQueue);
    // Setting Buffer Size and Number of Packets to Read
    UInt32 maxPacketSize;
    UInt32 propertySize=sizeof(maxPacketSize);
    // Getting audio File maximum packet size
    AudioFileGetProperty(AQPlayer.mAudioFile,kAudioFilePropertyPacketSizeUpperBound,&propertySize,&maxPacketSize);
    DeriveBufferSize(&AQPlayer.mDataFormat,maxPacketSize,0.5,&AQPlayer.bufferByteSize,&AQPlayer.mNumPacketsToRead);
    //   Allocating memory for a packet descriptions array
    bool isFormatVBR=(AQPlayer.mDataFormat.mBytesPerPacket == 0 ||
                      AQPlayer.mDataFormat.mFramesPerPacket == 0);
    if(isFormatVBR){
        AQPlayer.mPacketDecs=(AudioStreamPacketDescription*)malloc(AQPlayer.mNumPacketsToRead*sizeof(AudioStreamPacketDescription));
    }
    else{
        AQPlayer.mPacketDecs=NULL;
    }
    //  Setting a magic cookie for a playback audio queue
    UInt32 cookieSize=sizeof(UInt32);
    // Captures the result of the AudioFileGetPropertyInfo function. If successful, this function returns a value of NoErr, equivalent to Boolean false.
    bool couldNotGetProperty=AudioFileGetProperty(AQPlayer.mAudioFile,kAudioFilePropertyMagicCookieData,&cookieSize,NULL);
    if(!couldNotGetProperty && cookieSize){
        char* magicCookie=malloc(cookieSize);

        AudioFileGetProperty(AQPlayer.mAudioFile,kAudioFilePropertyMagicCookieData,&cookieSize,magicCookie);

        AudioQueueSetProperty(AQPlayer.mQueue,kAudioQueueProperty_MagicCookie,magicCookie,cookieSize);

        free(magicCookie);
    }
    AQPlayer.mCurrentPacket=0;
    for(int i =0;i<kNumberBuffers;++i){
        AudioQueueAllocateBuffer(AQPlayer.mQueue,AQPlayer.bufferByteSize,&AQPlayer.mBuffers[i]);
        HandleOutputBuffer(&AQPlayer,AQPlayer.mQueue,AQPlayer.mBuffers[i]);
    }
    Float32 gain=1.0; // Set Full Volume for playback
    AudioQueueSetParameter(AQPlayer.mQueue,kAudioQueueParam_Volume,gain);
    // start and play
    AQPlayer.isRunning=true;
    AudioQueueStart(AQPlayer.mQueue,NULL);
    do{
        CFRunLoopRunInMode(kCFRunLoopDefaultMode,0.25,false);
    }while(AQPlayer.isRunning);
    CFRunLoopRunInMode(kCFRunLoopDefaultMode,1,false);

     // Cleaning up after playing an audio file
    AudioQueueDispose(AQPlayer.mQueue,true);
    AudioFileClose(AQPlayer.mAudioFile);
    free(AQPlayer.mPacketDecs);
    return 0;
}

一切都可以正确构建和编译，但是当应用运行时，即使将 kAudioQueueParam_Volume设置为1.0，我也听不到扬声器或耳机的声音

Answer 1

这可能是由于在完全调用音频回调之前，退出了一个命令行应用程序，并且该调用被调用了足够的时间以覆盖文件的整个长度。您需要一些代码(运行循环和/或NSTimer？)来防止应用退出。