界面

- (void)openVideoCapture {
    self.session = [[AVCaptureSession alloc] init];
    [self.session setSessionPreset:AVCaptureSessionPreset640x480];
    AVCaptureVideoPreviewLayer *previewLayer = [AVCaptureVideoPreviewLayer layerWithSession:self.session];
    UIView *cameraView = [[UIView alloc] initWithFrame:CGRectMake(0, 0, SCREEN_WIDTH, SCREEN_HEIGHT)];
    previewLayer.frame = cameraView.bounds;
    [cameraView.layer addSublayer:previewLayer];
    [self.view addSubview:cameraView];
    // 摄像头以及视频输入
    AVCaptureDevice *videoDevice = [AVCaptureDevice defaultDeviceWithMediaType:AVMediaTypeVideo];
    videoDevice = [self cameraWithPosition:AVCaptureDevicePositionFront];
    NSError *error = nil;
    AVCaptureDeviceInput *videoInput = [AVCaptureDeviceInput deviceInputWithDevice:videoDevice error:&error];
    if ([self.session canAddInput:videoInput]) {
        [self.session addInput:videoInput];
    }
    AVCaptureVideoDataOutput *videoOutput = [[AVCaptureVideoDataOutput alloc] init];
    videoOutput.videoSettings = [NSDictionary dictionaryWithObject:
                                 [NSNumber numberWithUnsignedInt:kCVPixelFormatType_420YpCbCr8BiPlanarVideoRange]forKey:(NSString *)kCVPixelBufferPixelFormatTypeKey];
    [videoOutput setAlwaysDiscardsLateVideoFrames:YES];
    if ([_session canAddOutput:videoOutput] == NO)
    {
        YGNLog(@"Couldn't add video output");
        return ;
    }
    [_session addOutput:videoOutput];
    _videoConnection = [videoOutput connectionWithMediaType:AVMediaTypeVideo];// 设置采集图像的方向,如果不设置，采集回来的图形会是旋转90度的
    _videoConnection.videoOrientation = AVCaptureVideoOrientationPortrait;
    
    dispatch_queue_t queue = dispatch_queue_create("VideoCaptureQueue", DISPATCH_QUEUE_SERIAL);// 摄像头采集queue
    [videoOutput setSampleBufferDelegate:self queue:queue];
    _h264File = fopen([[NSString stringWithFormat:@"%@/vt_encode.h264", self.documentDictionary] UTF8String], "wb");
    //麦克风以及音频输入
    AVCaptureDevice *audioDevice = [AVCaptureDevice defaultDeviceWithMediaType:AVMediaTypeAudio];
    AVCaptureDeviceInput *audioInput = [AVCaptureDeviceInput deviceInputWithDevice:audioDevice error:&error];
    if ([self.session canAddInput:audioInput]) {
        [self.session addInput:audioInput];
    }
    AVCaptureAudioDataOutput *audioOutput = [[AVCaptureAudioDataOutput alloc] init];
    
    dispatch_queue_t queue1 = dispatch_queue_create("AudioCaptureQueue", DISPATCH_QUEUE_SERIAL);// 摄像头采集queue
    [audioOutput setSampleBufferDelegate:self queue:queue1];
    if ([_session canAddOutput:audioOutput] == NO)
    {
        YGNLog(@"Couldn't add audio output");
        return ;
    }
    _audioConnection = [audioOutput connectionWithMediaType:AVMediaTypeAudio];
    [_session addOutput:audioOutput];
    // 文件保存在document文件夹下，可以直接通过iTunes将文件导出到电脑，在plist文件中添加Application supports iTunes file sharing = YES
   [self.session commitConfiguration];
    return ;
}

代理方法

#pragma mark - AVCaptureAudioDataOutputSampleBufferDelegate
- (void)captureOutput:(AVCaptureOutput *)captureOutput didOutputSampleBuffer:(CMSampleBufferRef)sampleBuffer fromConnection:(AVCaptureConnection *)connection {
    
    if (_mediuChatType == YGMessageChatCallType_AudioReceive || _mediuChatType == YGMessageChatCallType_AudioCall) {
//        NSData *PCMData = [self convertAudioSmapleBufferToPcmData:sampleBuffer];
        if (ipTestString != nil && [YGUDPNatManager sharedManager].isUdpNatTranting == YES) {
//            YGNLog(@"PCMData.length======%lu",(unsigned long)PCMData.length);
//            [[YGUDPNatManager sharedManager] sendTestData:PCMData withIP:ipTestString withPort:1234];
        }
    } else {
        //视频采集
        if(connection == _videoConnection){
            [self encodeFrame:sampleBuffer];
            
        }else{
            NSData* data =  [self convertAudioSmapleBufferToPcmData:sampleBuffer];
            if(data) {
                [_audioData appendData:data];
            }
           
        }
    }
}

音频MP3处理

//提取pcm
-(NSData *) convertAudioSmapleBufferToPcmData:(CMSampleBufferRef) audioSample{
    //获取pcm数据大小
    NSInteger audioDataSize = CMSampleBufferGetTotalSampleSize(audioSample);
    
    //分配空间
    int8_t *audio_data = malloc((int32_t)audioDataSize);
    
    //获取CMBlockBufferRef
    //这个结构里面就保存了 PCM数据
    CMBlockBufferRef dataBuffer = CMSampleBufferGetDataBuffer(audioSample);
    //直接将数据copy至我们自己分配的内存中
    CMBlockBufferCopyDataBytes(dataBuffer, 0, audioDataSize, audio_data);
    NSData *pcmData = [NSData dataWithBytesNoCopy:audio_data length:audioDataSize];
    //返回数据
    return pcmData;
}

#pragma mark ---------pcm 转MP3

- (void)conventToMp3 {
    NSLog(@"convert begin!!");
    NSString *cafFilePath = [[YGMessageMediaUtily sharedMediaUtily] stringPathWithType:YGMessageMediaType_ImFile sessionID:0 mType:0 fileName:@"vt_encode.pcm"];
    NSString *mp3FilePath = [[NSHomeDirectory() stringByAppendingFormat:@"/Documents/"] stringByAppendingPathComponent:@"vy_encode.mp3"];
    @try {
        int read, write;
        FILE *pcm = fopen([cafFilePath cStringUsingEncoding:NSASCIIStringEncoding], "rb");
        fseek(pcm, 4*1024, SEEK_CUR);
        FILE *mp3 = fopen([mp3FilePath cStringUsingEncoding:NSASCIIStringEncoding], "wb");
        const int PCM_SIZE = 8192;
        const int MP3_SIZE = 8192;
        short int pcm_buffer[PCM_SIZE * 2];
        unsigned char mp3_buffer[MP3_SIZE];
        lame_t lame = lame_init();
        lame_set_in_samplerate(lame,22000);//采样播音速度，值越大播报速度越快，反之。
        lame_set_brate(lame,128);
        lame_set_num_channels(lame, 2);
        lame_set_mode(lame,MONO);
        lame_set_quality (lame, 2); /* 2=high 5 = medium 7=low 音 质 */
        lame_set_VBR(lame, vbr_default);
        lame_init_params(lame);
        do {
            read = (int)fread(pcm_buffer, 2 * sizeof(short int), PCM_SIZE, pcm);
            if (read == 0)
                write = lame_encode_flush(lame, mp3_buffer, MP3_SIZE);
            else
                write = lame_encode_buffer_interleaved(lame, pcm_buffer, read, mp3_buffer, MP3_SIZE);
            
            fwrite(mp3_buffer, write, 1, mp3);
            
        } while (read != 0);

        lame_close(lame);
        fclose(mp3);
        fclose(pcm);
    }
    @catch (NSException *exception) {
        NSLog(@"%@", [exception description]);
    }
    @finally {
        NSLog(@"convert mp3 finish!!!");
    }
}
===========挂断的时候调用==============
 [YGUDPNatManager sharedManager].isUdpNatTranting = YES;
    [[YGMessageMediaUtily sharedMediaUtily] storeData:_audioData forFileName:@"vt_encode.pcm" sessionID:0 type:YGMessageMediaType_ImFile mType:0];//存储数据到本地
    [self conventToMp3];

视频h264处理

- (int)startEncodeSession:(int)width height:(int)height framerate:(int)fps bitrate:(int)bt
{
    OSStatus status;
    _frameCount = 0;
    
    VTCompressionOutputCallback cb = encodeOutputCallback;
    status = VTCompressionSessionCreate(kCFAllocatorDefault, width, height, kCMVideoCodecType_H264, NULL, NULL, NULL, cb, (__bridge void *)(self), &_encodeSesion);
    
    if (status != noErr) {
        NSLog(@"VTCompressionSessionCreate failed. ret=%d", (int)status);
        return -1;
    }
    
    // 设置实时编码输出，降低编码延迟
    status = VTSessionSetProperty(_encodeSesion, kVTCompressionPropertyKey_RealTime, kCFBooleanTrue);
    NSLog(@"set realtime  return: %d", (int)status);
    
    // h264 profile, 直播一般使用baseline，可减少由于b帧带来的延时
    status = VTSessionSetProperty(_encodeSesion, kVTCompressionPropertyKey_ProfileLevel, kVTProfileLevel_H264_Baseline_AutoLevel);
    NSLog(@"set profile   return: %d", (int)status);
    
    // 设置编码码率(比特率)，如果不设置，默认将会以很低的码率编码，导致编码出来的视频很模糊
    status  = VTSessionSetProperty(_encodeSesion, kVTCompressionPropertyKey_AverageBitRate, (__bridge CFTypeRef)@(bt)); // bps
    status += VTSessionSetProperty(_encodeSesion, kVTCompressionPropertyKey_DataRateLimits, (__bridge CFArrayRef)@[@(bt*2/8), @1]); // Bps
    NSLog(@"set bitrate   return: %d", (int)status);
    
    // 设置关键帧间隔，即gop size
    status = VTSessionSetProperty(_encodeSesion, kVTCompressionPropertyKey_MaxKeyFrameInterval, (__bridge CFTypeRef)@(fps*2));
    
    // 设置帧率，只用于初始化session，不是实际FPS
    status = VTSessionSetProperty(_encodeSesion, kVTCompressionPropertyKey_ExpectedFrameRate, (__bridge CFTypeRef)@(fps));
    NSLog(@"set framerate return: %d", (int)status);
    
    // 开始编码
    status = VTCompressionSessionPrepareToEncodeFrames(_encodeSesion);
    NSLog(@"start encode  return: %d", (int)status);
    
    return 0;
}
// 编码一帧图像，使用queue，防止阻塞系统摄像头采集线程
- (void) encodeFrame:(CMSampleBufferRef )sampleBuffer
{
    dispatch_sync(_encodeQueue, ^{
        CVImageBufferRef imageBuffer = (CVImageBufferRef)CMSampleBufferGetImageBuffer(sampleBuffer);
        
        // pts,必须设置，否则会导致编码出来的数据非常大，原因未知
        CMTime pts = CMTimeMake(_frameCount, 1000);
        CMTime duration = kCMTimeInvalid;
        
        VTEncodeInfoFlags flags;
        
        // 送入编码器编码
        OSStatus statusCode = VTCompressionSessionEncodeFrame(_encodeSesion,
                                                              imageBuffer,
                                                              pts, duration,
                                                              NULL, NULL, &flags);
        
        if (statusCode != noErr) {
            NSLog(@"H264: VTCompressionSessionEncodeFrame failed with %d", (int)statusCode);
            
            [self stopEncodeSession];
            return;
        }
    });
}
- (void) stopEncodeSession
{
    VTCompressionSessionCompleteFrames(_encodeSesion, kCMTimeInvalid);
    
    VTCompressionSessionInvalidate(_encodeSesion);
    
    CFRelease(_encodeSesion);
    _encodeSesion = NULL;
}
// 编码回调，每当系统编码完一帧之后，会异步掉用该方法，此为c语言方法
void encodeOutputCallback(void *userData, void *sourceFrameRefCon, OSStatus status, VTEncodeInfoFlags infoFlags,
                          CMSampleBufferRef sampleBuffer )
{
    if (status != noErr) {
        NSLog(@"didCompressH264 error: with status %d, infoFlags %d", (int)status, (int)infoFlags);
        return;
    }
    if (!CMSampleBufferDataIsReady(sampleBuffer))
    {
        NSLog(@"didCompressH264 data is not ready ");
        return;
    }
    YGVideoChatViewController* vc = (__bridge YGVideoChatViewController*)userData;
    
    // 判断当前帧是否为关键帧
    bool keyframe = !CFDictionaryContainsKey( (CFArrayGetValueAtIndex(CMSampleBufferGetSampleAttachmentsArray(sampleBuffer, true), 0)), kCMSampleAttachmentKey_NotSync);
    
    // 获取sps & pps数据. sps pps只需获取一次，保存在h264文件开头即可
    if (keyframe && !vc->_spsppsFound)
    {
        size_t spsSize, spsCount;
        size_t ppsSize, ppsCount;
        
        const uint8_t *spsData, *ppsData;
        
        CMFormatDescriptionRef formatDesc = CMSampleBufferGetFormatDescription(sampleBuffer);
        OSStatus err0 = CMVideoFormatDescriptionGetH264ParameterSetAtIndex(formatDesc, 0, &spsData, &spsSize, &spsCount, 0 );
        OSStatus err1 = CMVideoFormatDescriptionGetH264ParameterSetAtIndex(formatDesc, 1, &ppsData, &ppsSize, &ppsCount, 0 );
        
        if (err0==noErr && err1==noErr)
        {
            vc->_spsppsFound = 1;
            [vc writeH264Data:(void *)spsData length:spsSize addStartCode:YES];
            [vc writeH264Data:(void *)ppsData length:ppsSize addStartCode:YES];
            NSLog(@"got sps/pps data. Length: sps=%zu, pps=%zu", spsSize, ppsSize);
        }
    }
    
    size_t lengthAtOffset, totalLength;
    char *data;
    
    CMBlockBufferRef dataBuffer = CMSampleBufferGetDataBuffer(sampleBuffer);
    OSStatus error = CMBlockBufferGetDataPointer(dataBuffer, 0, &lengthAtOffset, &totalLength, &data);
    
    if (error == noErr) {
        size_t offset = 0;
        const int lengthInfoSize = 4; // 返回的nalu数据前四个字节不是0001的startcode，而是大端模式的帧长度length
        
        // 循环获取nalu数据
        while (offset < totalLength - lengthInfoSize) {
            uint32_t naluLength = 0;
            memcpy(&naluLength, data + offset, lengthInfoSize); // 获取nalu的长度，
            // 大端模式转化为系统端模式
            naluLength = CFSwapInt32BigToHost(naluLength);
            
            NSLog(@"got nalu data, length=%d, totalLength=%zu", naluLength, totalLength);
            // 保存nalu数据到文件
            [vc writeH264Data:data+offset+lengthInfoSize length:naluLength addStartCode:YES];
            // 读取下一个nalu，一次回调可能包含多个nal H264: VTCompressionSessionEncodeFrame failed with -12902u
            offset += lengthInfoSize + naluLength;
        }
    }
}

// 保存h264数据到文件
- (void) writeH264Data:(void*)data length:(size_t)length addStartCode:(BOOL)b
{
    // 添加4字节的 h264 协议 start code
    const Byte bytes[] = "\x00\x00\x00\x01";
    
    if (_h264File) {
        if(b)
            fwrite(bytes, 1, 4, _h264File);
        
        fwrite(data, 1, length, _h264File);
        NSLog(@"save success");
    } else {
        NSLog(@"_h264File null error, check if it open successed");
    }
}


-  (void)viewDidAppear:(BOOL)animated {
    [self startEncodeSession:480 height:640 framerate:25 bitrate:640*1000];
    [_session startRunning];
}

总结

此处视频是实时转，视频中的音频是先存为pcm文件。然后挂断的时候将 pcm 转为MP3。另外，在转MP3
的时候 采样率以及相关参数一定要设置对。如果有变音就是采样率的问题。有问题或有补充的盆友欢迎底下留言。