iOS音视频采集和H264编码

将会为大家演示如何采集实时视屏资料，然后实时开始进行H264编码。

1、采集实时视屏数据

（1）、获取新建AVCaptureSession：

    self.cCapturesession = [[AVCaptureSession alloc] init];
    ///设置捕捉分辨率
    self.cCapturesession.sessionPreset = AVCaptureSessionPreset640x480;

（2）、使用函数dispath_get_global_queue去得到队列

    //使用函数dispath_get_global_queue去得到队列
    cCaptureQueue = dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0);
    cEncodeQueue = dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0);

（3）、获取输入摄像头并且通过AVCaptureDeviceInput包起来添加到cCapturesession里面去

    AVCaptureDeviceDiscoverySession *devicesSession = [AVCaptureDeviceDiscoverySession discoverySessionWithDeviceTypes:@[AVCaptureDeviceTypeBuiltInWideAngleCamera] mediaType:AVMediaTypeVideo position:AVCaptureDevicePositionUnspecified];//[AVCaptureDevice devicesWithMediaType:AVMediaTypeVideo];
    for (AVCaptureDevice *device in devicesSession.devices) {
        //拿到后置摄像头
        if ([device position] == AVCaptureDevicePositionBack) {
            inputCamera = device;
        }
    }
    
    //将捕捉设备 封装成 AVCaptureDeviceInput 对象
    self.cCaptureDeviceInput = [[AVCaptureDeviceInput alloc] initWithDevice:inputCamera error:nil];
    //判断是否能加入后置摄像头作为输入设备
    if ([self.cCapturesession canAddInput:self.cCaptureDeviceInput]) {
        //将设备添加到会话中
        [self.cCapturesession addInput:self.cCaptureDeviceInput];
    }

（3）、配置输出和创建连接

    //配置输出
    self.cCaptureDataOurput = [[AVCaptureVideoDataOutput alloc] init];
    //设置丢弃最后的video frame 为NO
    [self.cCaptureDataOurput setAlwaysDiscardsLateVideoFrames:NO];
    //设置video的视频捕捉的像素点压缩方式为 420
    NSDictionary *videoSettingDict = [NSDictionary dictionaryWithObject:[NSNumber numberWithInt:kCVPixelFormatType_420YpCbCr8BiPlanarFullRange] forKey:(id)kCVPixelBufferPixelFormatTypeKey];
    [self.cCaptureDataOurput setVideoSettings:videoSettingDict];
    
    //设置捕捉代理 和 捕捉队列
    [self.cCaptureDataOurput setSampleBufferDelegate:self queue:self->cCaptureQueue];
    //判断是否能添加输出
    if ([self.cCapturesession canAddOutput:self.cCaptureDataOurput]) {
        //添加输出
        [self.cCapturesession addOutput:self.cCaptureDataOurput];
    }
    
    //创建连接
    AVCaptureConnection *connection = [self.cCaptureDataOurput connectionWithMediaType:AVMediaTypeVideo];
    //设置连接的方向
    [connection setVideoOrientation:AVCaptureVideoOrientationPortrait];

通过代理传出采集到的视频数据
#pragma mark - AVCaptureVideoDataOutputSampleBufferDelegate
//AV Foundation 获取到视频流
- (void)captureOutput:(AVCaptureOutput *)output didOutputSampleBuffer:(CMSampleBufferRef)sampleBuffer fromConnection:(AVCaptureConnection *)connection
{
    NSLog(@"didOutputSampleBuffer:%@",sampleBuffer);
    //开始视频录制，获取到摄像头的视频帧，传入encode 方法中
    dispatch_sync(cEncodeQueue, ^{
        [self encode:sampleBuffer];
    });
}

初始化图层

 //初始化图层
    self.cPreviewLayer = [[AVCaptureVideoPreviewLayer alloc] initWithSession:self.cCapturesession];
    //设置视频重力
    [self.cPreviewLayer setVideoGravity:AVLayerVideoGravityResizeAspect];
    //设置图层的frame
    [self.cPreviewLayer setFrame:self.view.bounds];
    //添加图层
    [self.view.layer addSublayer:self.cPreviewLayer];

创建文件写入沙盒路径

    //文件写入沙盒
    NSString *filePath = [[NSSearchPathForDirectoriesInDomains(NSDocumentDirectory,NSUserDomainMask,YES)lastObject]stringByAppendingPathComponent:@"hsz_video.h264"];
    //先移除已存在的文件
    [[NSFileManager defaultManager] removeItemAtPath:filePath error:nil];
    
    //新建文件
    BOOL createFile = [[NSFileManager defaultManager] createFileAtPath:filePath contents:nil attributes:nil];
    if (!createFile) {
        
        NSLog(@"create file failed");
    }else
    {
        NSLog(@"create file success");

    }
    
    NSLog(@"filePaht = %@",filePath);
    fileHandle = [NSFileHandle fileHandleForWritingAtPath:filePath];

2、采集实时视屏数据进行H264编码

(1)、初始化videoToolBox设置编码是相关参数这里包括了创建编码session、丢弃B帧

设置码率、设置帧率.

- (void)initVideoToolBox
{
   dispatch_async(cEncodeQueue, ^{
       self->fremeID = 0;
       int width = 480,height = 640;
       //1.调用VTCompressionSessionCreate创建编码session
       //参数1：NULL 分配器,设置NULL为默认分配
       //参数2：width
       //参数3：height
       //参数4：编码类型,如kCMVideoCodecType_H264
       //参数5：NULL encoderSpecification: 编码规范。设置NULL由videoToolbox自己选择
       //参数6：NULL sourceImageBufferAttributes: 源像素缓冲区属性.设置NULL不让videToolbox创建,而自己创建
       //参数7：NULL compressedDataAllocator: 压缩数据分配器.设置NULL,默认的分配
       //参数8：回调  当VTCompressionSessionEncodeFrame被调用压缩一次后会被异步调用.注:当你设置NULL的时候,你需要调用VTCompressionSessionEncodeFrameWithOutputHandler方法进行压缩帧处理,支持iOS9.0以上
       //参数9：outputCallbackRefCon: 回调客户定义的参考值
       //参数10：compressionSessionOut: 编码会话变量
       OSStatus status = VTCompressionSessionCreate(NULL, width, height, kCMVideoCodecType_H264, NULL, NULL, NULL, didCompressH264, (__bridge void *)self, &self->cEncodeingSession);
       NSLog(@"H264:VTCompressionSessionCreate:%d",(int)status);
       if (status != 0) {
           NSLog(@"H264:Unable to create a H264 session");
           return ;
       }
       //设置实时编码输出（避免延迟）
       VTSessionSetProperty(self->cEncodeingSession, kVTCompressionPropertyKey_RealTime, kCFBooleanTrue);
       VTSessionSetProperty(self->cEncodeingSession, kVTCompressionPropertyKey_ProfileLevel, kVTProfileLevel_H264_Baseline_AutoLevel);
       
       //是否产生B帧(因为B帧在解码时并不是必要的,是可以抛弃B帧的)
       VTSessionSetProperty(self->cEncodeingSession, kVTCompressionPropertyKey_AllowFrameReordering, kCFBooleanFalse);
       //设置关键帧（GOPsize）间隔，GOP太小的话图像会模糊
       int frameInterval = 10;
       CFNumberRef fameIntervalRef = CFNumberCreate(kCFAllocatorDefault, kCFNumberIntType, &frameInterval);
       VTSessionSetProperty(self->cEncodeingSession, kVTCompressionPropertyKey_MaxKeyFrameInterval, fameIntervalRef);
       
       //设置期望帧率，不是实际帧率
       int fps = 10;
       CFNumberRef fpsRef = CFNumberCreate(kCFAllocatorDefault, kCFNumberIntType, &fps);
       VTSessionSetProperty(self->cEncodeingSession, kVTCompressionPropertyKey_ExpectedFrameRate, fpsRef);
       
       //码率的理解：码率大了话就会非常清晰，但同时文件也会比较大。码率小的话，图像有时会模糊，但也勉强能看
       //码率计算公式，参考印象笔记
       //设置码率、上限、单位是bps
       int bitRate = width * height * 3 * 4 * 8;
       CFNumberRef bitRateRef = CFNumberCreate(kCFAllocatorDefault, kCFNumberSInt32Type, &bitRate);
       VTSessionSetProperty(self->cEncodeingSession, kVTCompressionPropertyKey_AverageBitRate, bitRateRef);
       
       //设置码率，均值，单位是byte
       int bigRateLimit = width * height * 3 * 4;
       CFNumberRef bitRateLimitRef = CFNumberCreate(kCFAllocatorDefault, kCFNumberSInt32Type, &bigRateLimit);
       VTSessionSetProperty(self->cEncodeingSession, kVTCompressionPropertyKey_DataRateLimits, bitRateLimitRef);
       
       //开始编码
       VTCompressionSessionPrepareToEncodeFrames(self->cEncodeingSession);
       
   });
}

(2)、编码完成回调包括处理第一帧的sps、pps，并且写进沙河里面如图所示

/*
 1.H264硬编码完成后，回调VTCompressionOutputCallback
 2.将硬编码成功的CMSampleBuffer转换成H264码流，通过网络传播
 3.解析出参数集SPS & PPS，加上开始码组装成 NALU。提现出视频数据，将长度码转换为开始码，组成NALU，将NALU发送出去。
 */
void didCompressH264(void *outputCallbackRefCon, void *sourceFrameRefCon, OSStatus status,VTEncodeInfoFlags infoFlags,CMSampleBufferRef sampleBuffer)
{
    NSLog(@"didCompressH264 called with status %d infoFlags %d",(int)status,(int)infoFlags);
    //状态错误
    if (status != 0) {
        return;
    }
    //没准备好
    if (!CMSampleBufferDataIsReady(sampleBuffer)) {
        NSLog(@"didCompressH264 data is not ready");
        return;
    }
    
    ViewController *encoder = (__bridge  ViewController*)outputCallbackRefCon;
    
    //判断当前帧是否为关键帧
    /* 分步骤判断
    CFArrayRef array = CMSampleBufferGetSampleAttachmentsArray(sampleBuffer, true);
    CFDictionaryRef dic = CFArrayGetValueAtIndex(array, 0);
    bool isKeyFrame = !CFDictionaryContainsKey(dic, kCMSampleAttachmentKey_NotSync);
    */
    CFArrayRef array = CMSampleBufferGetSampleAttachmentsArray(sampleBuffer, true);
    CFDictionaryRef theDict = CFArrayGetValueAtIndex(array, 0);
    bool keyFrame = !CFDictionaryContainsKey(theDict, kCMSampleAttachmentKey_NotSync);
    //判断当前帧是否为关键帧
    //获取sps & pps 数据 只获取1次，保存在h264文件开头的第一帧中
    //sps(sample per second 采样次数/s),是衡量模数转换（ADC）时采样速率的单位
    //pps()
    if (keyFrame) {
        //图像存储方式，编码器等格式描述
        CMFormatDescriptionRef format = CMSampleBufferGetFormatDescription(sampleBuffer);
        //sps
        size_t sparameterSetSize,sparameterSetCount;
        const uint8_t *sparameterSet;
        OSStatus statusCode = CMVideoFormatDescriptionGetH264ParameterSetAtIndex(format, 0, &sparameterSet, &sparameterSetSize, &sparameterSetCount, 0);

        if (statusCode == noErr) {
            //获取pps
            size_t pparameterSetSize,pparameterSetCount;
            const uint8_t *pparameterSet;
            //从第一个关键帧获取sps & pps
            OSStatus statusCode = CMVideoFormatDescriptionGetH264ParameterSetAtIndex(format, 1, &pparameterSet, &pparameterSetSize, &pparameterSetCount, 0);
            
            //获取H264参数集合中的SPS和PPS
            if (statusCode == noErr) {
                //Found pps & sps
                NSData *sps = [NSData dataWithBytes:sparameterSet length:sparameterSetSize];
                NSData *pps = [NSData dataWithBytes:pparameterSet length:pparameterSetSize];
                
                if (encoder) {
                    [encoder gotSpsPps:sps pps:pps];
                }
            }
            
            //Found pps & sps
//            NSData *sps = [NSData dataWithBytes:sparameterSet length:sparameterSetSize];
//            NSData *pps = [NSData dataWithBytes:pp length:<#(NSUInteger)#>];
        }
    }
    
    CMBlockBufferRef dataBuffer = CMSampleBufferGetDataBuffer(sampleBuffer);
    size_t length,totalLength;
    char *dataPointer;
    OSStatus statusCodeRet = CMBlockBufferGetDataPointer(dataBuffer, 0, &length, &totalLength, &dataPointer);
    if (statusCodeRet == noErr) {
        size_t bufferOffset = 0;
        //返回的nalu数据前4个字节不是001的startcode,而是大端模式的帧长度length
        static const int AVCCHeaderLength = 4;
        //循环获取nalu数据
        while (bufferOffset < totalLength - AVCCHeaderLength) {
            uint32_t NALUnitLength = 0;
            //读取 一单元长度的 nalu
            memcpy(&NALUnitLength, dataPointer + bufferOffset, AVCCHeaderLength);
            //从大端模式转换为系统端模式
            NALUnitLength = CFSwapInt32BigToHost(NALUnitLength);
            //获取nalu数据
            NSData *data = [[NSData alloc] initWithBytes:(dataPointer + bufferOffset + AVCCHeaderLength)  length:NALUnitLength];
            //将nalu数据写入到文件
            [encoder gotEncodedData:data isKeyFrame:keyFrame];
            //move to the next NAL unit in the block buffer
            //读取下一个nalu 一次回调可能包含多个nalu数据
            bufferOffset += AVCCHeaderLength + NALUnitLength;
        }
    }
}

H264文件.png

(3)、通过采集视频代理返回进行实时的H264编码

A、通过代理传出采集到的视频数据
#pragma mark - AVCaptureVideoDataOutputSampleBufferDelegate
//AV Foundation 获取到视频流
- (void)captureOutput:(AVCaptureOutput *)output didOutputSampleBuffer:(CMSampleBufferRef)sampleBuffer fromConnection:(AVCaptureConnection *)connection
{
    NSLog(@"didOutputSampleBuffer:%@",sampleBuffer);
    //开始视频录制，获取到摄像头的视频帧，传入encode 方法中
    dispatch_sync(cEncodeQueue, ^{
        [self encode:sampleBuffer];
    });
}

B、对采集到的视频数据进行编码
///获取视频流开始编码
- (void)encode:(CMSampleBufferRef)sampleBuffer
{
    //拿到每一帧未编码数据
    CVImageBufferRef imageBuffer = (CVImageBufferRef)CMSampleBufferGetImageBuffer(sampleBuffer);
    //设置帧时间，如果不设置会导致时间轴过长。
    CMTime presentationTimeStamp = CMTimeMake(self->fremeID++, 100);
    VTEncodeInfoFlags flags;
    //参数1：编码会话变量
    //参数2：未编码数据
    //参数3：获取到的这个sample buffer数据的展示时间戳。每一个传给这个session的时间戳都要大于前一个展示时间戳.
    //参数4：对于获取到sample buffer数据,这个帧的展示时间.如果没有时间信息,可设置kCMTimeInvalid.
    //参数5：frameProperties: 包含这个帧的属性.帧的改变会影响后边的编码帧.
    //参数6：ourceFrameRefCon: 回调函数会引用你设置的这个帧的参考值.
    //参数7：infoFlagsOut: 指向一个VTEncodeInfoFlags来接受一个编码操作.如果使用异步运行,kVTEncodeInfo_Asynchronous被设置；同步运行,kVTEncodeInfo_FrameDropped被设置；设置NULL为不想接受这个信息.
    OSStatus statusCode = VTCompressionSessionEncodeFrame(self->cEncodeingSession, imageBuffer, presentationTimeStamp, kCMTimeInvalid, NULL, NULL, &flags);
    if (statusCode != noErr) {
        NSLog(@"H.264:VTCompressionSessionEncodeFrame faild with %d",(int)statusCode);
        VTCompressionSessionInvalidate(cEncodeingSession);
        CFRelease(cEncodeingSession);
        cEncodeingSession = NULL;
        return;
    }
    NSLog(@"H264:VTCompressionSessionEncodeFrame Success");
}

这是具体的Demo，有帮助在github点个星星 源码Demo