ios音视频编解码demo ios开发音视频编解码

在iOS中，Core Audio提供的一套软件接口来处理音频，支持录音、播放、声音效果、格式转换、文件流解析等。现在常用的场景是网络传输过来的音频流播放，在Core Audio中，可以使用Audio Queue或者OpenAL实现。

audio queue可以录音或播放，它的作用主要是：

·连接音频的硬件部分

·管理内存

·对于压缩的音频格式，能使用编解码codec

·调节录音与播放

下面重点看看audio queue对于音频流的处理：

图片看上去挺复杂，但主要的步骤就两步：

1、将音频数据送入buffer

2、数据播放后，再给对应的buffer补充数据

AudioQueueBufferRef）要一定格式组装好，送入buffer后就能自动播放声音。

了解这点，进一步理解就容易理解多了。

详细的介绍：

开源audio queue代码：音视频播放器：https://github.com/durfu/DFURTSPPlayer

在本例中，应用从第三方的库（tutk平台）中得到音频传输数据G711 mu-law，然后转换成pcm格式，通过Audio Queue播放。

G711 mu-law转pcm

int G711Decode(char* pRawData,const unsigned char* pBuffer, int nBufferSize)
{
    short *out_data = (short*)pRawData;
    int i = 0;
    for(; i<nBufferSize; i++)
    {
//        参考文档：
//          out_data[i] = (short)ulaw2linear((unsigned char)pBuffer[i]);

        int v = ulaw2linear((unsigned char)pBuffer[i]);
        out_data[i] = v < -32768 ? -32768 : v > 32767 ? 32767 : v;
    }
    
    return nBufferSize * 2;
}

int ulaw2linear(unsigned char u_val)
{
    int		t;
    
    /* Complement to obtain normal u-law value. */
    u_val = ~u_val;
    
    /*
     * Extract and bias the quantization bits. Then
     * shift up by the segment number and subtract out the bias.
     */
    t = ((u_val & QUANT_MASK) << 3) + BIAS;
    t <<= ((unsigned)u_val & SEG_MASK) >> SEG_SHIFT;
    
    return ((u_val & SIGN_BIT) ? (BIAS - t) : (t - BIAS));
}

2、audio queue播放：

- ( void )play:( void *)pcmData length:( unsigned int )length送入数据及长度即可

#import "PCMDataPlayer.h"

//audio queue运行流程：
//1、新建AudioQueueNewOutput，设置每个buffer用完后的回调，新建audio queue buffer（AudioQueueAllocateBuffer）
//2、外界传来一帧音频数据，找到闲置的一个buffer，将数据塞到buffer里，然后enqueue到audio queue中

@implementation PCMDataPlayer

- (id)init
{
    self = [super init];
    if (self) {
        [self reset];
    }
    return self;
}

- (void)dealloc
{
    if (audioQueue != nil) {
        AudioQueueStop(audioQueue, true);
    }
    audioQueue = nil;

    sysnLock = nil;

    NSLog(@"PCMDataPlayer dealloc...");
}

static void AudioPlayerAQInputCallback(void* inUserData, AudioQueueRef outQ, AudioQueueBufferRef outQB)
{
    PCMDataPlayer* player = (__bridge PCMDataPlayer*)inUserData;
    [player playerCallback:outQB];
}

- (void)reset
{
    [self stop];

    sysnLock = [[NSLock alloc] init];

    ///设置音频参数
    audioDescription.mSampleRate = 8000; //采样率
    audioDescription.mFormatID = kAudioFormatLinearPCM;
    audioDescription.mFormatFlags = kLinearPCMFormatFlagIsSignedInteger | kAudioFormatFlagIsPacked;
    audioDescription.mChannelsPerFrame = 1; ///单声道
    audioDescription.mFramesPerPacket = 1; //每一个packet一侦数据
    audioDescription.mBitsPerChannel = 16; //每个采样点16bit量化
    audioDescription.mBytesPerFrame = (audioDescription.mBitsPerChannel / 8) * audioDescription.mChannelsPerFrame;
    audioDescription.mBytesPerPacket = audioDescription.mBytesPerFrame;

    AudioQueueNewOutput(&audioDescription, AudioPlayerAQInputCallback, (__bridge void*)self, nil, nil, 0, &audioQueue); //使用player的内部线程播放

    //初始化音频缓冲区
    for (int i = 0; i < QUEUE_BUFFER_SIZE; i++) {
        int result = AudioQueueAllocateBuffer(audioQueue, MIN_SIZE_PER_FRAME, &audioQueueBuffers[i]); ///创建buffer区，MIN_SIZE_PER_FRAME为每一侦所需要的最小的大小，该大小应该比每次往buffer里写的最大的一次还大
//        NSLog(@"AudioQueueAllocateBuffer i = %d,result = %d", i, result);
    }

    NSLog(@"PCMDataPlayer reset");
}

- (void)stop
{
    if (audioQueue != nil) {
        AudioQueueStop(audioQueue, true);
        AudioQueueReset(audioQueue);
    }

    audioQueue = nil;
}

- (void)play:(void*)pcmData length:(unsigned int)length
{
    if (audioQueue == nil || ![self checkBufferHasUsed]) {
        [self reset];
        AudioQueueStart(audioQueue, NULL);
    }

    [sysnLock lock];

    AudioQueueBufferRef audioQueueBuffer = NULL;

    while (true) {
        audioQueueBuffer = [self getNotUsedBuffer];
        if (audioQueueBuffer != NULL) {
            break;
        }
        usleep(1000);
    }

    audioQueueBuffer->mAudioDataByteSize = length;
    Byte* audiodata = (Byte*)audioQueueBuffer->mAudioData;
    for (int i = 0; i < length; i++) {
        audiodata[i] = ((Byte*)pcmData)[i];
    }

    AudioQueueEnqueueBuffer(audioQueue, audioQueueBuffer, 0, NULL);

//    NSLog(@"PCMDataPlayer play dataSize:%d", length);

    [sysnLock unlock];
}

- (BOOL)checkBufferHasUsed
{
    for (int i = 0; i < QUEUE_BUFFER_SIZE; i++) {
        if (YES == audioQueueUsed[i]) {
            return YES;
        }
    }
//    NSLog(@"PCMDataPlayer 播放中断............");
    return NO;
}

- (AudioQueueBufferRef)getNotUsedBuffer
{
    for (int i = 0; i < QUEUE_BUFFER_SIZE; i++) {
        if (NO == audioQueueUsed[i]) {
            audioQueueUsed[i] = YES;
//            NSLog(@"PCMDataPlayer play buffer index:%d", i);
            return audioQueueBuffers[i];
        }
    }
    return NULL;
}

- (void)playerCallback:(AudioQueueBufferRef)outQB
{
    for (int i = 0; i < QUEUE_BUFFER_SIZE; i++) {
        if (outQB == audioQueueBuffers[i]) {   //现存的buffer与回调的buffer一致，就表示没用过
            audioQueueUsed[i] = NO;
        }
    }
}

@end