ffmpeg(7)：将h264编码的视频流保存为BMP或者JPEG图片

时间：2025-01-24 12:04:27

一般我们知道播放视频流的时候是有截图功能的。

所以我想是否可以将视频流保存为BMP或者JPEG


参考：

1.最简单的基于FFMPEG的图像编码器（YUV编码为JPEG）

/leixiaohua1020/article/details/25346147

2. 


视频帧保存为BMP


#define __STDC_CONSTANT_MACROS


#ifdef _WIN32
//Windows
extern "C"
{
#include "libavcodec/"
#include "libavformat/"
#include "libswscale/"
#include ""
};
#else
//Linux...
#ifdef __cplusplus
extern "C"
{
#endif
#include <libavcodec/>
#include <libavformat/>
#include <libswscale/>
#include <SDL2/>
#ifdef __cplusplus
};
#endif
#endif



//保存BMP文件的函数
void SaveAsBMP(AVFrame *pFrameRGB, int width, int height, int index, int bpp)
{
    char buf[5] = {0};
    BITMAPFILEHEADER bmpheader;
    BITMAPINFOHEADER bmpinfo;
    FILE *fp;

    char *filename = new char[255];

    //文件存放路径，根据自己的修改
    sprintf_s(filename, 255, "%s%", "E:/temp/", index);
    if( (fp = fopen(filename,"wb+")) == NULL ) {
        printf ("open file failed!\n");
        return;
    }

     = 0x4d42;
    bmpheader.bfReserved1 = 0;
    bmpheader.bfReserved2 = 0;
     = sizeof(BITMAPFILEHEADER) + sizeof(BITMAPINFOHEADER);
     =  + width*height*bpp/8;

     = sizeof(BITMAPINFOHEADER);
     = width;
     = height;
     = 1;
     = bpp;
     = BI_RGB;
     = (width*bpp+31)/32*4*height;
     = 100;
     = 100;
     = 0;
     = 0;

    fwrite(&bmpheader, sizeof(bmpheader), 1, fp);
    fwrite(&bmpinfo, sizeof(bmpinfo), 1, fp);
    fwrite(pFrameRGB->data[0], width*height*bpp/8, 1, fp);

    fclose(fp);
}



DWORD Work_Save2BMP()
{
    int videoStream = -1;
    AVCodecContext *pCodecCtx;
    AVFormatContext *pFormatCtx;
    AVCodec *pCodec;
    AVFrame *pFrame, *pFrameRGB;
    struct SwsContext *pSwsCtx;
    const char *filename = "bigbuckbunny_480x272.h264";
    AVPacket packet;
    int frameFinished;
    int PictureSize;
    uint8_t *outBuff;

    //注册编解码器
    av_register_all();
    // 初始化网络模块
    avformat_network_init();
    // 分配AVFormatContext
    pFormatCtx = avformat_alloc_context();

    //打开视频文件
    if( avformat_open_input(&pFormatCtx, filename, NULL, NULL) != 0 ) {
        printf ("av open input file failed!\n");
        exit (1);
    }

    //获取流信息
    if( avformat_find_stream_info(pFormatCtx, NULL) < 0 ) {
        printf ("av find stream info failed!\n");
        exit (1);
    }
    //获取视频流
    for( int i = 0; i < pFormatCtx->nb_streams; i++ ) {
        if ( pFormatCtx->streams[i]->codec->codec_type == AVMEDIA_TYPE_VIDEO ) {
            videoStream = i;
            break;
        }
    }
    if( videoStream == -1 ) {
        printf ("find video stream failed!\n");
        exit (1);
    }

    // 寻找解码器
    pCodecCtx = pFormatCtx->streams[videoStream]->codec;
    pCodec = avcodec_find_decoder(pCodecCtx->codec_id);
    if( pCodec == NULL ) {
        printf ("avcode find decoder failed!\n");
        exit (1);
    }

    //打开解码器
    if( avcodec_open2(pCodecCtx, pCodec, NULL) < 0 ) {
        printf ("avcode open failed!\n");
        exit (1);
    }

    //为每帧图像分配内存
    pFrame = avcodec_alloc_frame();
    pFrameRGB = avcodec_alloc_frame();
    if( (pFrame == NULL) || (pFrameRGB == NULL) ) {
        printf("avcodec alloc frame failed!\n");
        exit (1);
    }

    // 确定图片尺寸
    PictureSize = avpicture_get_size(PIX_FMT_BGR24, pCodecCtx->width, pCodecCtx->height);
    outBuff = (uint8_t*)av_malloc(PictureSize);
    if( outBuff == NULL ) {
        printf("av malloc failed!\n");
        exit(1);
    }
    avpicture_fill((AVPicture *)pFrameRGB, outBuff, PIX_FMT_BGR24, pCodecCtx->width, pCodecCtx->height);

    //设置图像转换上下文
    pSwsCtx = sws_getContext(pCodecCtx->width, pCodecCtx->height, pCodecCtx->pix_fmt,
        pCodecCtx->width, pCodecCtx->height, PIX_FMT_BGR24,
        SWS_BICUBIC, NULL, NULL, NULL);

    int i = 0;
    while( av_read_frame(pFormatCtx, &packet) >= 0 ) {
        if( packet.stream_index == videoStream ) {
            avcodec_decode_video2(pCodecCtx, pFrame, &frameFinished, &packet);

            if( frameFinished ) {
                //反转图像 ，否则生成的图像是上下调到的
                pFrame->data[0] += pFrame->linesize[0] * (pCodecCtx->height - 1);
                pFrame->linesize[0] *= -1;
                pFrame->data[1] += pFrame->linesize[1] * (pCodecCtx->height / 2 - 1);
                pFrame->linesize[1] *= -1;
                pFrame->data[2] += pFrame->linesize[2] * (pCodecCtx->height / 2 - 1);
                pFrame->linesize[2] *= -1;

                //转换图像格式，将解压出来的YUV420P的图像转换为BRG24的图像
                sws_scale(pSwsCtx, pFrame->data,
                    pFrame->linesize, 0, pCodecCtx->height,
                    pFrameRGB->data, pFrameRGB->linesize);

                SaveAsBMP(pFrameRGB, pCodecCtx->width, pCodecCtx->height, i ++, 24);
            }
        } else {
            int a=2;
            int b=a;
        }

        av_free_packet(&packet);
    }

    sws_freeContext (pSwsCtx);
    av_free (pFrame);
    av_free (pFrameRGB);
    avcodec_close (pCodecCtx);
    avformat_close_input(&pFormatCtx);

    return 0;
}
其实总结起来就几点，
打开视频文件，将里面的每一帧取出来，并将其转换为RGB格式。
H264---(解码)-->YUV420---(转码).-->RGB---(保存)--->BMP


视频帧保存为JPEG

保存为JPEG和BMP有点类似，但是也有区别，具体流程是：
H264---(解码)-->YUV420---(转码).---(保存)--->JPEG 

#define __STDC_CONSTANT_MACROS


#ifdef _WIN32
//Windows
extern "C"
{
#include "libavcodec/"
#include "libavformat/"
#include "libswscale/"
#include ""
};
#else
//Linux...
#ifdef __cplusplus
extern "C"
{
#endif
#include <libavcodec/>
#include <libavformat/>
#include <libswscale/>
#include <SDL2/>
#ifdef __cplusplus
};
#endif
#endif



/**
 * 将AVFrame(YUV420格式)保存为JPEG格式的图片
 *
 * @param width YUV420的宽
 * @param height YUV42的高
 *
 */
int MyWriteJPEG(AVFrame* pFrame, int width, int height, int iIndex)
{
    // 输出文件路径
    char out_file[MAX_PATH] = {0};
    sprintf_s(out_file, sizeof(out_file), "%s%", "E:/temp/", iIndex);
    
    // 分配AVFormatContext对象
    AVFormatContext* pFormatCtx = avformat_alloc_context();
    
    // 设置输出文件格式
    pFormatCtx->oformat = av_guess_format("mjpeg", NULL, NULL);
    // 创建并初始化一个和该url相关的AVIOContext
    if( avio_open(&pFormatCtx->pb, out_file, AVIO_FLAG_READ_WRITE) < 0) {
        printf("Couldn't open output file.");
        return -1;
    }
    
    // 构建一个新stream
    AVStream* pAVStream = avformat_new_stream(pFormatCtx, 0);
    if( pAVStream == NULL ) {
        return -1;
    }
    
    // 设置该stream的信息
    AVCodecContext* pCodecCtx = pAVStream->codec;
    
    pCodecCtx->codec_id = pFormatCtx->oformat->video_codec;
    pCodecCtx->codec_type = AVMEDIA_TYPE_VIDEO;
    pCodecCtx->pix_fmt = PIX_FMT_YUVJ420P;
    pCodecCtx->width = width;
    pCodecCtx->height = height;
    pCodecCtx->time_base.num = 1;
    pCodecCtx->time_base.den = 25;
    
    // Begin Output some information
    av_dump_format(pFormatCtx, 0, out_file, 1);
    // End Output some information
    
    // 查找解码器
    AVCodec* pCodec = avcodec_find_encoder(pCodecCtx->codec_id);
    if( !pCodec ) {
        printf("Codec not found.");
        return -1;
    }
    // 设置pCodecCtx的解码器为pCodec
    if( avcodec_open2(pCodecCtx, pCodec, NULL) < 0 ) {
        printf("Could not open codec.");
        return -1;
    }
    
    //Write Header
    avformat_write_header(pFormatCtx, NULL);
    
    int y_size = pCodecCtx->width * pCodecCtx->height;
    
    //Encode
    // 给AVPacket分配足够大的空间
    AVPacket pkt;
    av_new_packet(&pkt, y_size * 3);
    
    // 
    int got_picture = 0;
    int ret = avcodec_encode_video2(pCodecCtx, &pkt, pFrame, &got_picture);
    if( ret < 0 ) {
        printf("Encode Error.\n");
        return -1;
    }
    if( got_picture == 1 ) {
        //pkt.stream_index = pAVStream->index;
        ret = av_write_frame(pFormatCtx, &pkt);
    }

    av_free_packet(&pkt);

    //Write Trailer
    av_write_trailer(pFormatCtx);

    printf("Encode Successful.\n");

    if( pAVStream ) {
        avcodec_close(pAVStream->codec);
    }
    avio_close(pFormatCtx->pb);
    avformat_free_context(pFormatCtx);
    
    return 0;
}

DWORD Work_Save2JPG()
{
    int videoStream = -1;
    AVCodecContext *pCodecCtx;
    AVFormatContext *pFormatCtx;
    AVCodec *pCodec;
    AVFrame *pFrame, *pFrameRGB;
    struct SwsContext *pSwsCtx;
    const char *filename = "bigbuckbunny_480x272.h264";
    AVPacket packet;
    int frameFinished;
    int PictureSize;
    uint8_t *outBuff;

    //注册编解码器
    av_register_all();
    // 初始化网络模块
    avformat_network_init();
    // 分配AVFormatContext
    pFormatCtx = avformat_alloc_context();

    //打开视频文件
    if( avformat_open_input(&pFormatCtx, filename, NULL, NULL) != 0 ) {
        printf ("av open input file failed!\n");
        exit (1);
    }

    //获取流信息
    if( avformat_find_stream_info(pFormatCtx, NULL) < 0 ) {
        printf ("av find stream info failed!\n");
        exit (1);
    }
    //获取视频流
    for( int i = 0; i < pFormatCtx->nb_streams; i++ ) {
        if ( pFormatCtx->streams[i]->codec->codec_type == AVMEDIA_TYPE_VIDEO ) {
            videoStream = i;
            break;
        }
    }
    if( videoStream == -1 ) {
        printf ("find video stream failed!\n");
        exit (1);
    }

    // 寻找解码器
    pCodecCtx = pFormatCtx->streams[videoStream]->codec;
    pCodec = avcodec_find_decoder(pCodecCtx->codec_id);
    if( pCodec == NULL ) {
        printf ("avcode find decoder failed!\n");
        exit (1);
    }

    //打开解码器
    if( avcodec_open2(pCodecCtx, pCodec, NULL) < 0 ) {
        printf ("avcode open failed!\n");
        exit (1);
    }

    //为每帧图像分配内存
    pFrame = avcodec_alloc_frame();
    pFrameRGB = avcodec_alloc_frame();
    if( (pFrame == NULL) || (pFrameRGB == NULL) ) {
        printf("avcodec alloc frame failed!\n");
        exit (1);
    }

    // 确定图片尺寸
    PictureSize = avpicture_get_size(PIX_FMT_YUVJ420P, pCodecCtx->width, pCodecCtx->height);
    outBuff = (uint8_t*)av_malloc(PictureSize);
    if( outBuff == NULL ) {
        printf("av malloc failed!\n");
        exit(1);
    }
    avpicture_fill((AVPicture *)pFrameRGB, outBuff, PIX_FMT_YUVJ420P, pCodecCtx->width, pCodecCtx->height);

    //设置图像转换上下文
    pSwsCtx = sws_getContext(pCodecCtx->width, pCodecCtx->height, pCodecCtx->pix_fmt,
        pCodecCtx->width, pCodecCtx->height, PIX_FMT_YUVJ420P,
        SWS_BICUBIC, NULL, NULL, NULL);

    int i = 0;
    while( av_read_frame(pFormatCtx, &packet) >= 0 ) {
        if( packet.stream_index == videoStream ) {
            avcodec_decode_video2(pCodecCtx, pFrame, &frameFinished, &packet);

            if( frameFinished ) {
                // 保存为jpeg时不需要反转图像
                static bool b1 = true;
                if( b1 ) {
                    MyWriteJPEG(pFrame, pCodecCtx->width, pCodecCtx->height, i ++);
                    
                    b1 = false;
                }
                
                //SaveAsBMP(pFrameRGB, pCodecCtx->width, pCodecCtx->height, i ++, 24);
            }
        } else {
            int a=2;
            int b=a;
        }

        av_free_packet(&packet);
    }

    sws_freeContext(pSwsCtx);

    av_free(pFrame);
    av_free(pFrameRGB);
    avcodec_close(pCodecCtx);
    avformat_close_input(&pFormatCtx);

    return 0;
}

这里需要对 
MyWriteJPEG
函数做点说明：
在调用avformat_new_stream前，pFormatCtx的nb_streams为0，表明当前没有流，调用avformat_new_stream后，该值为1.
表明我们新建了一个流，然后下面就是设定该流的相关信息。










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