X264编码2 实时编码（USB摄像头）

    上一篇我们介绍了X264的编码，但是只能对本地文件编码，这里讨论怎么实时的读取摄像头文件并编码。

    利用opencv实时读取摄像头，可以参考博客：点击打开链接。这里不做过多介绍。

    至于编码流程，和上篇一样，没有改变。我们了解下X264编码器怎么直接读取摄像头的一帧图像就行。

    opencv打开摄像头时，一帧一帧的播放，每一帧都由frame指定：capture >> frame

    当然这里还有问题，X264对输入的要求是YUV格式，但是经过opencv采集后一帧frame是RGB格式，所以在编码之前我们要先将格式转换下，利用opencv自带的函数cvtColor。

    cv::cvtColor(frame, yuvImg, CV_BGR2YUV_I420)

    函数原型：

    void cvCvtColor(const CvArr* src，CvArr* dst，int code)         src：输入； dst：输出； code：转换的模式；

    转换后的数据保存在yuvImg中，并通过fwrite函数写出，这里写出的数据是YUV格式，直接将其送到X264编码器的接口处就能开始编码。

    最后给出完整代码：

#include 
#include 
#include 
#include 
#include "stdafx.h"
#include "stdint.h"
#include "opencv2/highgui/highgui.hpp"
#include "opencv2/imgproc/imgproc.hpp"

extern "C"
{
#include "x264.h"
#include "x264_config.h"
};

using namespace cv;
using namespace std;

int MyYuvtoH264(int width, int height, string filename)
{
	int fps = 25;
	size_t yuv_size = width * height * 3 / 2;
	x264_t *encoder;
	x264_picture_t pic_in, pic_out;
	uint8_t *yuv_buffer;

	x264_param_t param;
	x264_param_default_preset(¶m, "veryfast", "zerolatency");
	param.i_threads = 1;
	param.i_width = width;
	param.i_height = height;
	param.i_fps_num = fps;
	param.i_fps_den = 1;
	param.i_keyint_max = 25;
	param.b_intra_refresh = 1;
	param.b_annexb = 1;

	x264_param_apply_profile(¶m, "baseline");
	encoder = x264_encoder_open(¶m);
	x264_picture_alloc(&pic_in, X264_CSP_I420, width, height);
	yuv_buffer = (uint8_t*)malloc(yuv_size);

	pic_in.img.plane[0] = yuv_buffer;
	pic_in.img.plane[1] = pic_in.img.plane[0] + width * height;
	pic_in.img.plane[2] = pic_in.img.plane[1] + width * height / 4;

	int64_t i_pts = 0;
	x264_nal_t *nals;
	int nnal;

	FILE *inf = fopen(filename.c_str(), "rb");
	FILE *outf = fopen("test.h264", "wb");
	if (NULL == inf)
	{
		return -1;
	}

	while (fread(yuv_buffer, 1, yuv_size, inf) > 0)
	{
		pic_in.i_pts = i_pts++;
		x264_encoder_encode(encoder, &nals, &nnal, &pic_in, &pic_out);
		x264_nal_t *nal;
		for (nal = nals; nal < nals + nnal; nal++)
		{
			fwrite(nal->p_payload, 1, nal->i_payload, outf);
		}
	}
	x264_encoder_close(encoder);

	fclose(inf);
	fclose(outf);
	free(yuv_buffer);
	return 0;
}

int main(int argc, char* argv[])
{
	VideoCapture capture(0);
	if (!capture.isOpened())  
	{
		cout << "Cannot open the video cam" << endl;
		return -1;
	}

	int w = capture.get(CV_CAP_PROP_FRAME_WIDTH);
	int h = capture.get(CV_CAP_PROP_FRAME_HEIGHT);
	int yuv_bufLen = w * h * 3 / 2;
	unsigned char* pYuvBuf = new unsigned char[yuv_bufLen];

	FILE* pFileOut = fopen("result.yuv", "w+");
	if (!pFileOut)
	{
		printf("pFileOut open error \n");
		system("pause");
		exit(-1);
	}
	printf("pFileOut open ok \n");

	cout << "Frame size : " << w << " x " << h << endl;
	namedWindow("opencamera", CV_WINDOW_AUTOSIZE);
	while (1)
	{
		Mat frame;
		capture >> frame;
		imshow("opencamera", frame); 
		if (waitKey(30) == 27) break;	

		cv::Mat yuvImg;
		cv::cvtColor(frame, yuvImg, CV_BGR2YUV_I420);
		memcpy(pYuvBuf, yuvImg.data, yuv_bufLen*sizeof(unsigned char));
		fwrite(pYuvBuf, yuv_bufLen*sizeof(unsigned char), 1, pFileOut);
		MyYuvtoH264(w, h, "result.yuv");
	}

	waitKey(0);
	fclose(pFileOut);
	delete[] pYuvBuf;
	Sleep(100);
	return 0;
}	

   

    上面介绍的代码是读取了一帧数据，然后对一帧图片编码，没有很好的利用帧间压缩。而且编码器在每次读取一张图片时，都要重新打开，重新关闭，这样明显是错误的，压缩效率不够。所以现在修改下代码，编码器打开后一直运行，等待图片的输入，修改参数在编码前缓存几张，打开帧间编码，提高压缩效率。

    下面是修改后的完整代码：

#include <stdio.h>
#include <iostream>
#include "stdafx.h"
#include "stdint.h"
#include "opencv2/highgui/highgui.hpp"
#include "opencv2/imgproc/imgproc.hpp"

extern "C"
{
#include "x264.h"
#include "x264_config.h"
};

using namespace cv;
using namespace std;

int main(int argc, char* argv[])
{
	VideoCapture capture(0);
	if (!capture.isOpened())
	{
		cout << "Cannot open the video cam" << endl;
		return -1;
	}

	int w = capture.get(CV_CAP_PROP_FRAME_WIDTH);
	int h = capture.get(CV_CAP_PROP_FRAME_HEIGHT);

	int yuv_bufLen = w * h * 3 / 2;

	size_t yuv_size = w * h * 3 / 2;
	x264_t *encoder;
	x264_picture_t pic_in, pic_out;
	uint8_t *yuv_buffer;

	x264_param_t param;
	x264_param_default_preset(¶m, "veryfast", "animation");
	param.i_width = w;            
	param.i_height = h;           

	x264_param_apply_profile(¶m, "baseline");    

	encoder = x264_encoder_open(¶m);     
	x264_picture_alloc(&pic_in, X264_CSP_I420, w, h);    
	yuv_buffer = (uint8_t*)malloc(yuv_size);     

	pic_in.img.plane[0] = yuv_buffer;       
	pic_in.img.plane[1] = pic_in.img.plane[0] + w * h;
	pic_in.img.plane[2] = pic_in.img.plane[1] + w * h / 4;

	int64_t i_pts = 0;
	x264_nal_t *nals;
	int nnal;

	FILE *fp_out = fopen("test.h264", "wb");
	if (!fp_out)
	{
		printf("Could not open output 264 file\n");
		return -1;
	}
	FILE* pFileOut = fopen("test.yuv", "w+");
	if (!pFileOut)
	{
		printf("Could not open input yuv file\n");
		return -1;
	}

	cout << "Frame size : " << w << " x " << h << endl;
	namedWindow("opencamera", CV_WINDOW_AUTOSIZE);
	Mat frame;

	while (1)
	{
		capture >> frame;             
		imshow("opencamera", frame);  
		waitKey(1);

		cv::Mat yuvImg;
		cv::cvtColor(frame, yuvImg, CV_BGR2YUV_I420);   
		memcpy(yuv_buffer, yuvImg.data, yuv_bufLen*sizeof(unsigned char));    
		fwrite(yuv_buffer, yuv_bufLen*sizeof(unsigned char), 1, pFileOut);    

		pic_in.i_pts = i_pts++;
		x264_encoder_encode(encoder, &nals, &nnal, &pic_in, &pic_out);  

		x264_nal_t *nal;
		for (nal = nals; nal < nals + nnal; nal++)
		{
			fwrite(nal->p_payload, 1, nal->i_payload, fp_out);     
		}
	}

	x264_encoder_close(encoder);  
	free(yuv_buffer);
	return 0;
}

    代码的运行效果图：