iOS视频推流格式转换

视频采集会得到格式为CMSampleBufferRef的视频包，视频推流一般把视频流转换成flv格式

(1)首先将视频流转换成YUV的数据格式

//获取yuv数据

- (NSData*)convertVideoSmapleBufferToYuvData:(CMSampleBufferRef)videoSample {

//通过CMSampleBufferGetImageBuffer方法，获得CVImageBufferRef，里面就包含了YUV420数据的指针

CVImageBufferRef pixelBuffer = CMSampleBufferGetImageBuffer(videoSample);

//锁住格式转换线程，开始转换格式

CVPixelBufferLockBaseAddress(pixelBuffer,0);

//获取图像宽度（像素）

size_t pixelWidth = CVPixelBufferGetWidth(pixelBuffer);

//获取图像高度（像素）

size_t pixelHeight = CVPixelBufferGetHeight(pixelBuffer);

//计算YUV中的Y所占字节数

size_t y_size = pixelWidth * pixelHeight;

//计算YUV中的U和V分别所占的字节数

size_t uv_size = y_size /4;

uint8_t * yuv_frame = aw_alloc(uv_size *2+ y_size);

//获取pixelBuffer中的Y数据

uint8_t * y_frame = CVPixelBufferGetBaseAddressOfPlane(pixelBuffer,0);

memcpy(yuv_frame, y_frame, y_size);

//获取pixelBuffer中的UV数据

uint8_t * uv_frame = CVPixelBufferGetBaseAddressOfPlane(pixelBuffer,1);

memcpy(yuv_frame + y_size, uv_frame, uv_size *2);

//获取到想要的数据，解锁格式转换线程

CVPixelBufferUnlockBaseAddress(pixelBuffer,0);

//yuv格式---->nv12格式

NSData * yuvData = [NSData dataWithBytesNoCopy:yuv_frame length:y_size + uv_size *2];

//由于相机偏转，我们需要对的到的视频页面进行旋转

 return [self rotateNV12Data:nv12Data];

}

（2）由于相机偏转，我们需要对的到的视频页面进行旋转

- (NSData*)rotateNV12Data:(NSData*)nv12Data {

int degree = 0;

switch(self.videoConfig.orientation) {

case UIInterfaceOrientationLandscapeLeft:

degree = 90;

break;

case UIInterfaceOrientationLandscapeRight:

degree = 270;

break;

default:

//do nothing

break;

}

if(degree !=0) {

uint8_ t * src_nv12_bytes = (uint8_t*)nv12Data.bytes;

uint32_t width = (uint32_t)self.videoConfig.width;

uint32_t height = (uint32_t)self.videoConfig.height;

uint32_t w_x_h = (uint32_t)(self.videoConfig.width*self.videoConfig.height);

uint8_t * rotatedI420Bytes =aw_alloc(nv12Data.length);

NV12ToI420Rotate(src_nv12_bytes, width,

    src_nv12_bytes + w_x_h, width,

    rotatedI420Bytes, height,

    rotatedI420Bytes + w_x_h, height /2,

    rotatedI420Bytes + w_x_h + w_x_h /4, height /2,

    width, height, (RotationModeEnum)degree);

    I420ToNV12(rotatedI420Bytes, height,

    rotatedI420Bytes + w_x_h, height /2,

    rotatedI420Bytes + w_x_h + w_x_h /4, height /2,

    src_nv12_bytes, height, src_nv12_bytes + w_x_h, height,

    height, width);

  aw_free(rotatedI420Bytes);

}

return nv12Data;

}

（3）将nv12格式的数据合成为flv格式

- (aw_flv_video_tag*)encodeYUVDataToFlvTag:(NSData*)yuvData{

if(!_vEnSession) {

return NULL;

}

OSStatus status = noErr;

//获取视频宽度

size_t pixelWidth = self.videoConfig.pushStreamWidth;

//获取视频高度

size_t pixelHeight = self.videoConfig.pushStreamHeight;

//NV12数据->CVPixelBufferRef中

//硬编码主要调用VTCompressionSessionEncodeFrame函数，此函数处理的是CVPixelBufferRef类型。

CVPixelBufferRef pixelBuf =NULL;

//初始化pixelBuf

CVPixelBufferCreate(NULL, pixelWidth, pixelHeight,kCVPixelFormatType_420YpCbCr8BiPlanarVideoRange,NULL, &pixelBuf);

if(CVPixelBufferLockBaseAddress(pixelBuf,0) != kCVReturnSuccess){

NSLog(@"encode video lock base address failed"); 

return NULL;

}

//将YUV数据填充到CVPixelBufferRef中

size_t y_size = aw_stride(pixelWidth) * pixelHeight;

size_t uv_size = y_size /4;

uint8_t * yuv_frame = (uint8_t*)yuvData.bytes;

//获取y frame

uint8_t * y_frame = CVPixelBufferGetBaseAddressOfPlane(pixelBuf,0);

memcpy(y_frame, yuv_frame, y_size);

//获取uv frame

uint8_t * uv_frame = CVPixelBufferGetBaseAddressOfPlane(pixelBuf,1);

memcpy(uv_frame, yuv_frame + y_size, uv_size *2);

//编码CMSampleBufRef

//获取时间戳，由于视频帧是有顺序的，所以timestamp可以自定义一个累加字段

uint32_t ptsMs = timestamp+1;//self.vFrameCount++ * 1000.f / self.videoConfig.fps;

CMTime pts =CMTimeMake(ptsMs,1000);

//将NV12数据的PixelBuf送到硬编码器中，进行编码。

status = VTCompressionSessionEncodeFrame(_vEnSession, pixelBuf, pts,kCMTimeInvalid,NULL, pixelBuf,NULL);

if(status == noErr) {

dispatch_semaphore_wait(self.vSemaphore,DISPATCH_TIME_FOREVER);

if(_naluData) {

//硬编码成功，_naluData内的数据即为h264视频帧。

//因为是推流，所以需要获取帧长度，转成大端字节序，放到数据的最前面

uint32_t naluLen = (uint32_t)_naluData.length;

//小端转大端。计算机内一般都是小端，而网络和文件中一般都是大端。大端转小端和小端转大端算法一样，就是字节序反转就行了。

uint8_t naluLenArr[4] = {naluLen >>24&0xff, naluLen >>16&0xff, naluLen >>8&0xff, naluLen &0xff};

//数据拼接

NSMutableData * mutableData = [NSMutableData dataWithBytes:naluLenArr length:4];

[mutableData appendData:_naluData];

//h264 -> flv tag，合成flvtag之后就可以直接发送到服务端了。

aw_flv_video_tag * video_tag = aw_encoder_create_video_tag((int8_t*)mutableData.bytes, mutableData.length, ptsMs,0,self.isKeyFrame);

//编码完成，释放数据。

_naluData = nil;

_isKeyFrame = NO;

CVPixelBufferUnlockBaseAddress(pixelBuf,0);

CFRelease(pixelBuf);

return video_tag;

}

}else {

NSLog(@"encode video frame error");

}

CVPixelBufferUnlockBaseAddress(pixelBuf,0);

CFRelease(pixelBuf);

return NULL;

}