【发布时间】：2016-03-11 21:10:43
【问题描述】：
我使用 Apple 音频队列服务指南制作了一个命令行类型的应用程序来播放磁盘中的文件
#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;
}
一切构建和编译都没有错误，但是当应用程序运行时，即使我将 kAudioQueueParam_Volume 设置为 1.0，我也听不到扬声器或耳机发出的任何声音
【问题讨论】：
标签： objective-c xcode audio operating-system core-audio