iPhone 音频总结

[http://www.helmsmansoft.com/index.php/archives/1141]

第一步呢。。先初始化AudioSession。为了实现中断的控制和后台，锁屏的播放状态

- (id)initsession {    
    AudioSessionInitialize (NULL, NULL, interruptionListenerCallback, self);
    UInt32 sessionCategory = kAudioSessionCategory_MediaPlayback;//采用后台和锁屏时仍继续播放的模式;
    AudioSessionSetProperty (kAudioSessionProperty_AudioCategory, sizeof (sessionCategory), &sessionCategory);
    UInt32 doSetProperty = 0;
    AudioSessionSetProperty (kAudioSessionProperty_OverrideCategoryMixWithOthers,sizeof (doSetProperty),&doSetProperty);
    AudioSessionSetActive (true);//激活AudioSession
    return self;
}
void interruptionListenerCallback (void    *inUserData, UInt32 interruptionState) {
    AudioPlayer *player = (AudioPlayer*)inUserData;
    if (interruptionState == kAudioSessionBeginInterruption) {
//使音乐暂停
        AudioWrapper * ad = [AudioWrapper sharedAudioWrapperElement];
        [ad pause];
    }
    else if (interruptionState == kAudioSessionEndInterruption ) {
        OSStatus rc = AudioSessionSetActive(true);
        if (rc) {
            NSLog(@"AudioSessionSetActive(true) returned %d", rc);
        }
//使音乐恢复播放
        AudioWrapper * ad = [AudioWrapper sharedAudioWrapperElement];
        [ad resume];
    }
}

第二步呢。。。为了接受在线过来的数据要使用媒体流功能，设置，最后解析NSData成为音频Buffer数据。。
先打开流媒体功能：

        error = AudioFileStreamOpen(
                                    (void*)self,                          
                                    &AudioFileStreamPropertyListenerProc, //监听设置变化
                                    &AudioFileStreamPacketsProc,     //数据解析后的接收函数 
                                    0,                                    
                                    &audio_file_stream);//媒体流的ID
void AudioFileStreamPropertyListenerProc(
   void *inClientData,
   AudioFileStreamID inAudioFileStream,
   AudioFileStreamPropertyID inPropertyID,
   UInt32 *ioFlags)
{
#ifdef KXT_DEBUG
    [ZPub LogTalk:@"AudioFileStreamPropertyListenerProc"];
#endif 
    ;
}
 
void AudioFileStreamPacketsProc(
   void *inClientData,
   UInt32 inNumberBytes,
   UInt32 inNumberPackets,
   const void *inInputData,
   AudioStreamPacketDescription *inPacketDescriptions) {
    [(AudioPlayer*)inClientData newAudioData:inInputData bytes:inNumberBytes packets:inNumberPackets packetDescriptions:inPacketDescriptions];//自己开始整理解析后的数据
}

然后再把NSData传给解码器解析：

    error = AudioFileStreamParseBytes(
                                      audio_file_stream,//在这时，媒体流文件ID被生成
                                      datalen,
                                      [data bytes],
                                      kAudioFileStreamProperty_FileFormat);

这样解码后的数据自动会被发送到AudioFileStreamPacketsProc接口里。。
第三步;准备Buffer数据（mAudioData（所有的Data），mAudioDataByteSize数据的大小，num_packets多少包，packet_descriptions包的描述）

- (id)initWithData:(NSData*)_data packets:(UInt32)_num_packets packetDescriptions:(const AudioStreamPacketDescription*)_packet_descriptions {
    if(!_data) 
        return nil;
    if(!_packet_descriptions)
        return nil;
    self = [super init];
    if(!self)
        return nil;
    self.data = _data;
    num_packets = _num_packets;
    packet_descriptions = malloc(num_packets * sizeof(AudioStreamPacketDescription));
    memcpy((void*)packet_descriptions, (const void*)_packet_descriptions, num_packets * sizeof(AudioStreamPacketDescription));
    return self;
}

第四步如果没有播放队列就创建播放队列。。。

  UInt32 formatListSize;
        Boolean b;//拿媒体流文件ID申请它的音乐格式结构信息
        AudioFileStreamGetPropertyInfo(audio_file_stream, 
                                       kAudioFileStreamProperty_FormatList, 
                                       &formatListSize, 
                                       &b);
 
        // now get the format data得到音乐格式信息
        NSMutableData *listData = [NSMutableData dataWithLength:formatListSize];
        OSStatus status = AudioFileStreamGetProperty(audio_file_stream, 
                                                     kAudioFileStreamProperty_FormatList, 
                                                     &formatListSize, 
                                                     [listData mutableBytes]);
        AudioFormatListItem *formatList = [listData mutableBytes];
 
        // The formatList property isn't always supported, so an error isn't unexpected here.
        // Therefore, we won't call VERIFY_STATUS on this status code.
        if (status == noErr) {
            // now see which format this device supports best
            UInt32 chosen;
            UInt32 chosenSize = sizeof(UInt32);
            int formatCount = formatListSize/sizeof(AudioFormatListItem);
            status = AudioFormatGetProperty ('fpfl', 
                                             formatListSize, 
                                             formatList, 
                                             &chosenSize, 
                                             &chosen);
            if (status == noErr) {
                audio_format = formatList[chosen].mASBD;//获取到具体的音乐格式（用于创建更好的播放队列）
 
 
            } else {
                // the docs tell us to grab the last in the list because it's most compatible
                audio_format = formatList[formatCount - 1].mASBD;
            }
        } else {
            // fall back to the stream's DataFormat
            UInt32 audio_format_size = sizeof(AudioStreamBasicDescription);
            error = AudioFileStreamGetProperty(audio_file_stream, 
                                                        kAudioFileStreamProperty_DataFormat, 
                                                        &audio_format_size, 
                                                        &audio_format);
 
            if(error){
                [buffer release];
                return;
            }
        }
 
 
        Float32 outValue ; 
        AudioQueueGetParameter(audio_queue,kAudioQueueDeviceProperty_NumberChannels,&outValue) ;
        if(![self createAudioQueue]){
            [buffer release];
            return;
        }
    }
- (BOOL)createAudioQueue {
 
    error = AudioQueueNewOutput(&audio_format, &MyAudioQueueOutputCallback, (void*)self, [[NSRunLoop currentRunLoop] getCFRunLoop], kCFRunLoopCommonModes, 0, &audio_queue);
}

最后。将准备好的buffer放到已创建的播放队列里就播放了。

    [buffer enqueueOnQueue:audio_queue];
 
- (void)enqueueOnQueue:(AudioQueueRef)queue {
 
    AudioQueueBufferRef buffer;
    error = AudioQueueAllocateBuffer(queue, [data length], &buffer);
    if(error) {
        [super dealloc];
        return;
    }
    buffer->mAudioDataByteSize = [data length];
    memcpy((char*)buffer->mAudioData, [data bytes], [data length]);
    error = AudioQueueEnqueueBuffer(queue, buffer, num_packets, packet_descriptions);
    if(error) {
        [ZPub LogTalk:[NSString stringWithFormat:@"AudioQueueEnqueueBuffer failed with %d", (int)error]];
        return;
    }
}