前言

本文主要针对他们的效率讨论为目的，而不做具体的转换分析。 在日常开发中，特别是在编解码的项目中，数据格式转换是很常见的，如YUV转RGB、YU12转I420、亦或者其他格式等等，我们常用的转换方式，要么使用Opencv的cvtColor()，要么使用FFmepg的sws_scale()，单帧图片进行转换还好，但如果我们在视频处理过程中使用，就会发现数据延迟，内存增长等各种问题，常见的处理方式是丢帧。最近尝试用LibYUV库来进行处理，发现效率还真不错。下面来进行三者的效率对比：

代码片

• 1、 通过FFmepg，YUV转RGB

bool YV12ToBGR24_FFmpeg(unsigned char* pYUV, unsigned char* pBGR24, int width, int height)
{
	if (width < 1 || height < 1 || pYUV == NULL || pBGR24 == NULL)
		return false;
	//int srcNumBytes,dstNumBytes;
	//uint8_t *pSrc,*pDst;
	AVPicture pFrameYUV, pFrameBGR;

	//pFrameYUV = avpicture_alloc();
	//srcNumBytes = avpicture_get_size(PIX_FMT_YUV420P,width,height);
	//pSrc = (uint8_t *)malloc(sizeof(uint8_t) * srcNumBytes);
	avpicture_fill(&pFrameYUV, pYUV, PIX_FMT_YUV420P, width, height);

	//U,V互换
	uint8_t * ptmp = pFrameYUV.data[1];
	pFrameYUV.data[1] = pFrameYUV.data[2];
	pFrameYUV.data[2] = ptmp;

	//pFrameBGR = avcodec_alloc_frame();
	//dstNumBytes = avpicture_get_size(PIX_FMT_BGR24,width,height);
	//pDst = (uint8_t *)malloc(sizeof(uint8_t) * dstNumBytes);
	avpicture_fill(&pFrameBGR, pBGR24, PIX_FMT_BGR24, width, height);

	struct SwsContext* imgCtx = NULL;
	imgCtx = sws_getContext(width, height, PIX_FMT_YUV420P, width, height, PIX_FMT_BGR24, SWS_BILINEAR, 0, 0, 0);

	if (imgCtx != NULL) {
		sws_scale(imgCtx, pFrameYUV.data, pFrameYUV.linesize, 0, height, pFrameBGR.data, pFrameBGR.linesize);
		if (imgCtx) {
			sws_freeContext(imgCtx);
			imgCtx = NULL;
		}
		return true;
	}
	else {
		sws_freeContext(imgCtx);
		imgCtx = NULL;
		return false;
	}
}

• 2、使用Opencv，YUV转RGB

void YVToBGR24_Opencv(unsigned char* pYUV, int width, int height)
{
	//unsigned char *data 存的是YUYV的裸数据；
	cv::Mat yuvImg;
	cv::Mat rgbImg(height, width, CV_8UC3);
	yuvImg.create(height, width, CV_8UC2);
	int len = width * height * 3 / 2;
	memcpy(yuvImg.data, pYUV, len);
	cv::cvtColor(yuvImg, rgbImg, CV_YUV2BGR_YUYV);
}

• 3、使用LibYUV，YUV转RGB

void YUVToRGB_LibYUV(uint8_t *y, uint8_t *u, uint8_t *v, unsigned char* pBGR24, int width, int hight)
{
	libyuv::I420ToARGB(y, width, u, width/2, v, width/2, (uint8_t*)pBGR24, width * 4, width, hight);
}

• 4、main函数

int main()
{
	const int width_src = 1920, height_src = 1080;
	const int width_dest = 640, height_dest = 320;
	FILE *src_file = NULL;
	FILE *dst_file = NULL;
	fopen_s(&src_file, "output.yuv", "rb");
	fopen_s(&dst_file, "output.rgb", "wb");

	int size_src = width_src * height_src * 3 / 2;
	int size_dest = width_dest * height_dest * 3 / 2;
	char *buffer_src = (char *)malloc(size_src);
	char *buffer_dest = (char *)malloc(size_dest);

	uint8_t *src_data[4];
	int src_linesize[4];

	uint8_t *dst_data[4];
	int dst_linesize[4];

	if (av_image_alloc(src_data, src_linesize, width_src, height_src, AV_PIX_FMT_YUV420P, 1) < 0) {
		return -1;
	}
	if (av_image_alloc(dst_data, dst_linesize, width_src, height_src, AV_PIX_FMT_BGRA, 1) < 0) {
		return -1;
	}

	while (1) {
		if (fread(buffer_src, 1, size_src, src_file) != size_src) {
			//fseek(src_file, 0, 0);
			//fread(buffer_src, 1, size_src, src_file);
			break;
		}
		memcpy(src_data[0], buffer_src, width_src * height_src);                    //Y
		memcpy(src_data[1], buffer_src + width_src * height_src, width_src * height_src / 4);      //U
		memcpy(src_data[2], buffer_src + width_src * height_src * 5 / 4, width_src * height_src / 4);  //V
		uint64_t start_time = os_gettime_ns();
		//YVToBGR24_Opencv(*src_data, width_src, height_src);
		//YV12ToBGR24_FFmpeg(*src_data, *dst_data, width_src, height_src);
		YUVToRGB_LibYUV(src_data[0], src_data[1], src_data[2], *dst_data, width_src, height_src);
		uint64_t stop_time = os_gettime_ns();
		printf("------ %ld\n", stop_time - start_time);
	}

	free(buffer_src);
	free(buffer_dest);
	fclose(dst_file);
	fclose(src_file);

	getchar();
	std::cout << "Hello World!\n";
}

效果图

结论

通过上图，我们能够粗略看出，FFmepg和Opencv的转换效率差不多，但LibYUV是他们的大概4倍。