ffmpeg对于摄像头采集的数据进行解码测试验证

之前在看别人代码的时候发现，有的博主在对摄像头采集的时候会先使用avcodec_decode_video2进行解码，让我很是不解，后来才知道是因为摄像头的不同，采集出来的数据有可能是经过了内部编码的数据，也有可能就是原始yuv数据，所以我这里做一个测试，看看如果是yuv数据的话，使用avcodec_decode_video2解码会不会有什么影响。结果证明是不会有影响的。直接上代码。

代码有参考博客主的文章：https://blog.youkuaiyun.com/li_wen01/article/details/62226563

#include <stdio.h>
#include <string.h>
#include <stdlib.h>
#include <unistd.h>
#include <string.h>
#include <time.h>
#include <sys/time.h>
#include <libavutil/frame.h>
#include <libavutil/mem.h>
#include <assert.h>

#include <libavcodec/avcodec.h>
#include <libavformat/avformat.h>
#include <libswresample/swresample.h>
#include <libavutil/time.h>
#include <libavutil/mathematics.h>


#include <libavcodec/avcodec.h>
#include <libavformat/avformat.h>
#include <libswscale/swscale.h>


#include <SDL.h>
#include <SDL_thread.h>

 
char* input_name= "video4linux2";
char* file_name = "/dev/video0";
char* out_file  = "yuv420.yuv";
 
void captureOneFrame(void){
    AVFormatContext *fmtCtx = NULL;    
    AVInputFormat 	*inputFmt;
    AVPacket 		*packet = NULL;
	AVCodecContext	*pCodecCtx = NULL;
	AVCodec 		*pCodec; 
	struct SwsContext *sws_ctx;  
    FILE *fp; 
	int i;
	int ret;
	int videoindex;
	
	enum AVPixelFormat dst_pix_fmt = AV_PIX_FMT_YUV420P;
    const char *dst_size = NULL;  
    const char *src_size = NULL;  
    uint8_t *src_data[4];   
    uint8_t *dst_data[4];  
    int src_linesize[4];  
    int dst_linesize[4];  
    int src_bufsize;  
    int dst_bufsize;  
    int src_w ;  
    int src_h ;  
    int dst_w = 1280;   
    int dst_h = 960;
 
    fp = fopen(out_file, "wb");    
    if (fp < 0)    {        
        printf("open frame data file failed\n");        
        return ;    
    }    
 
    inputFmt = av_find_input_format (input_name);    
   
    if (inputFmt == NULL)    {        
        printf("can not find_input_format\n");        
        return;    
    }    
 
    if (avformat_open_input ( &fmtCtx, file_name, inputFmt, NULL) < 0){
        printf("can not open_input_file\n");         return;    
    }
	
	av_dump_format(fmtCtx, 0, file_name, 0);
 
	videoindex= -1;
	for(i=0; i<fmtCtx->nb_streams; i++) 
		if(fmtCtx->streams[i]->codec->codec_type==AVMEDIA_TYPE_VIDEO){
			videoindex=i;
			break;
		}
	if(videoindex==-1){
		printf("Didn't find a video stream.\n");
		return -1;
	}
 
	pCodecCtx = fmtCtx->streams[videoindex]->codec;
	pCodec    = avcodec_find_decoder(pCodecCtx->codec_id); 

	if(avcodec_open2(pCodecCtx, pCodec,NULL)<0){
		printf("Could not open codec.\n");
		return -1;
	}


		AVFrame* pFrame = av_frame_alloc();
		AVFrame* pFrameYUV = av_frame_alloc();
		uint8_t* out_buffer=(uint8_t *)av_malloc(avpicture_get_size(AV_PIX_FMT_YUV420P, pCodecCtx->width, pCodecCtx->height));
		avpicture_fill((AVPicture *)pFrameYUV, out_buffer, AV_PIX_FMT_YUV420P, pCodecCtx->width, pCodecCtx->height);
		packet=(AVPacket *)av_malloc(sizeof(AVPacket));


	
    printf("picture width   =  %d \n", pCodecCtx->width);
    printf("picture height  =  %d \n", pCodecCtx->height);
    printf("Pixel   Format  =  %d \n", pCodecCtx->pix_fmt);
		
	sws_ctx =  sws_getContext(pCodecCtx->width, pCodecCtx->height, pCodecCtx->pix_fmt, 
		pCodecCtx->width, pCodecCtx->height, AV_PIX_FMT_YUV420P, SWS_BICUBIC, NULL, NULL, NULL);  
 
 
	int loop = 200;
	int got_picture = -1;
	//printf("开始编码了\n");
	while(loop--){
    	av_read_frame(fmtCtx, packet);
		if(packet->stream_index == videoindex){
		//	printf("找到视频流\n");
			avcodec_decode_video2(pCodecCtx, pFrame, &got_picture, packet);
			if (got_picture) {
			//	printf("编码成功\n");
			sws_scale(sws_ctx, (const uint8_t* const*)pFrame->data, pFrame->linesize, 0, pCodecCtx->height, 
					pFrameYUV->data, pFrameYUV->linesize);

    	fwrite(pFrameYUV->data[0], 1, pCodecCtx->width*pCodecCtx->height, fp);
		fwrite(pFrameYUV->data[1], 1, pCodecCtx->width*pCodecCtx->height/4, fp);
		fwrite(pFrameYUV->data[2], 1, pCodecCtx->width*pCodecCtx->height/4, fp);
			}
		}
		av_free_packet(packet);
	} 
    
    fclose(fp);    

	sws_freeContext(sws_ctx);
   	av_frame_free(&pFrameYUV);
	av_frame_free(&pFrame);
		avcodec_close(pCodecCtx);
    avformat_close_input(&fmtCtx);
 } 
 
int main(void){    
    avcodec_register_all();    
    avdevice_register_all();    
    captureOneFrame();    
    return 0;
}