音视频入门-7-ffmpeg小实验-v4l2 ubuntu 获取摄像头图像并进行格式转换

1.　　Linux内我们使用V4L2框架获取摄像头数据，由于摄像头的不同，摄像头所输出的数据格式各有不同。

　　   考虑到YUV420P 的格式使用最广泛，我们最终将摄像头数据转为该格式。

pic_data_transform.c

/*=============================================================================

 * #   Desc: use ffmpeg read a frame data from v4l2, and convert
 * #       the output data format 

 * =============================================================================*/
#include <stdio.h>
#include <string.h>
#include <stdlib.h>
#include <unistd.h>
#include <string.h>
#include "avformat.h"
#include "avcodec.h"
#include "avdevice.h"
#include <libavutil/imgutils.h>
#include <libswscale/swscale.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;
    AVCodecContext    *pCodecCtx;
    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); 

    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, dst_w, dst_h, dst_pix_fmt,
                             SWS_BILINEAR, NULL, NULL, NULL); 

    src_bufsize = av_image_alloc(src_data, src_linesize, pCodecCtx->width, pCodecCtx->height, pCodecCtx->pix_fmt, 16);
    dst_bufsize = av_image_alloc(dst_data, dst_linesize, dst_w, dst_h, dst_pix_fmt, 1);

    packet = (AVPacket *)av_malloc(sizeof(AVPacket));  

    int loop = 1000;
//    while(loop--){
        av_read_frame(fmtCtx, packet);
        memcpy(src_data[0], packet->data, packet->size);
        sws_scale(sws_ctx, src_data,  src_linesize, 0, pCodecCtx->height, dst_data, dst_linesize);
        fwrite(dst_data[0], 1, dst_bufsize, fp);
//    } 

    fclose(fp);
    av_free_packet(packet);
    av_freep(&dst_data[0]);
    sws_freeContext(sws_ctx);
    avformat_close_input(&fmtCtx);
 } 

int main(void){
    avcodec_register_all();
    avdevice_register_all();
    captureOneFrame();
    return 0;
}
 

代码备注：

FFmpeg中的 sws_scale() 函数主要是用来做视频像素格式和分辨率的转换，

其优势在于：可以在同一个函数里实现：1.图像色彩空间转换， 2:分辨率缩放，3:前后图像滤波处理。

不足之处在于：效率相对较低，不如libyuv或shader

下面博文进行了详细的解释， 顶一个

https://www.cnblogs.com/yongdaimi/p/10715830.html

makefile

OUT_APP         = test
INCLUDE_PATH = /usr/local/ffmpeg/include/
INCLUDE = -I$(INCLUDE_PATH) -I$(INCLUDE_PATH)libavutil/ -I$(INCLUDE_PATH)libavdevice/ \
            -I$(INCLUDE_PATH)libavcodec/ -I$(INCLUDE_PATH)libswresample \
            -I$(INCLUDE_PATH)libavfilter/ -I$(INCLUDE_PATH)libavformat \
            -I$(INCLUDE_PATH)libswscale/

LIB_PATH = /usr/local/ffmpeg/lib/
FFMPEG_LIBS = -L$(LIB_PATH) -lavformat -lavutil -lavdevice -lavcodec -lswresample -lavfilter -lswscale
SDL_LIBS    =
LIBS        = $(FFMPEG_LIBS)$(SDL_LIBS)

COMPILE_OPTS = $(INCLUDE)
C              = c
OBJ          = o
C_COMPILER   = cc
C_FLAGS      = $(COMPILE_OPTS) $(CPPFLAGS) $(CFLAGS)

LINK          = cc -o
LINK_OPTS    = -lz -lm  -lpthread
LINK_OBJ     = pic_data_transform.o 

.$(C).$(OBJ):
    $(C_COMPILER) -c -g $(C_FLAGS) $<

$(OUT_APP): $(LINK_OBJ)
    $(LINK)$@  $(LINK_OBJ)  $(LIBS) $(LINK_OPTS)

clean:
        -rm -rf *.$(OBJ) $(OUT_APP) core *.core *~  picture

编译运行记录

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