ffmpeg 把视频解码成jpg

这是一个h264视频解码的小demo，先把h264转成yuv,然后再把yuv转成jpg
#include <iostream>

int Frame2JPG(AVPacket packet, AVFrame* pFrame, unsigned int stream_index,
              int width, int height)
{
    // 输出文件路径
    char out_file[100] = { 0 };
    sprintf(out_file,"%s%d.jpg", "video/", packet.pts);

    // 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)
    {
        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 = AV_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)
    {
        return -1;
    }
    // 设置pCodecCtx的解码器为pCodec
    if (avcodec_open2(pCodecCtx, pCodec, NULL) < 0)
    {
        return -1;
    }

    //Write Header
    int ret = avformat_write_header(pFormatCtx, NULL);
    if (ret < 0)
    {
        return -1;
    }

    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;
    ret = avcodec_encode_video2(pCodecCtx, &pkt, pFrame, &got_picture);
    if (ret < 0)
    {
        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);

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

    return 0;
}

int decode_h264(char *filepath)
{
    AVFormatContext    *pFormatCtx;
    AVCodecContext    *pCodecCtx;
    AVCodec            *pCodec;
    AVFrame    *pFrame, *pFrameYUV;
    AVPacket *packet;
    struct SwsContext *img_convert_ctx;
    uint8_t *out_buffer;

    int    videoindex = -1;
    int y_size;
    int ret, got_picture;

    FILE *fp_yuv = fopen("1.yuv", "wb+");

    av_register_all();
    //avformat_network_init();
    pFormatCtx = avformat_alloc_context();

    if (avformat_open_input(&pFormatCtx, filepath, NULL, NULL) != 0)
    {
        printf("Couldn't open input stream.\n");
        return -1;
    }
    if (avformat_find_stream_info(pFormatCtx, NULL) <0)
    {
        printf("Couldn't find stream information.\n");
        return -1;
    }

    for (int i = 0; i < pFormatCtx->nb_streams; i++)
    {
        if (pFormatCtx->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 = pFormatCtx->streams[videoindex]->codec;

    // 根据编码器的ID查找FFmpeg的解码器
    pCodec = avcodec_find_decoder(pCodecCtx->codec_id);
    if (pCodec == NULL)
    {
        printf("Codec not found.\n");
        return -1;
    }
    // 初始化一个视音频编解码器的AVCodecContext
    if (avcodec_open2(pCodecCtx, pCodec, NULL)<0)
    {
        printf("Could not open codec.\n");
        return -1;
    }

    // 一些内存分配
    packet = (AVPacket *)av_malloc(sizeof(AVPacket));
    pFrame = av_frame_alloc();
    pFrameYUV = av_frame_alloc();
    out_buffer = (uint8_t *)av_malloc(avpicture_get_size(AV_PIX_FMT_YUV420P, pCodecCtx->width, pCodecCtx->height));
    // 为已经分配空间的结构体AVPicture挂上一段用于保存数据的空间
    // AVFrame/AVPicture有一个data[4]的数据字段,buffer里面存放的只是yuv这样排列的数据，
    // 而经过fill 之后，会把buffer中的yuv分别放到data[0],data[1],data[2]中。
    avpicture_fill((AVPicture *)pFrameYUV, out_buffer, AV_PIX_FMT_YUV420P, pCodecCtx->width, pCodecCtx->height);

    //Output Info-----------------------------
    printf("--------------- File Information ----------------\n");
    av_dump_format(pFormatCtx, 0, filepath, 0);
    printf("-------------------------------------------------\n");

    // 初始化一个SwsContext
    // 参数：源图像的宽，源图像的高，源图像的像素格式，目标图像的宽，目标图像的高，目标图像的像素格式，设定图像拉伸使用的算法
    img_convert_ctx = sws_getContext(pCodecCtx->width, pCodecCtx->height, pCodecCtx->pix_fmt,
                                     pCodecCtx->width, pCodecCtx->height, AV_PIX_FMT_YUV420P, SWS_BICUBIC, NULL, NULL, NULL);

    while (av_read_frame(pFormatCtx, packet) >= 0)
    {
        if (packet->stream_index == videoindex)
        {
            // 解码一帧视频数据。输入一个压缩编码的结构体AVPacket，输出一个解码后的结构体AVFrame
            ret = avcodec_decode_video2(pCodecCtx, pFrame, &got_picture, packet);
            if (ret < 0)
            {
                printf("Decode Error.\n");
                return -1;
            }
            if (got_picture)
            {
                // 转换像素
                sws_scale(img_convert_ctx, (const uint8_t* const*)pFrame->data, pFrame->linesize, 0, pCodecCtx->height,
                          pFrameYUV->data, pFrameYUV->linesize);

                y_size = pCodecCtx->width * pCodecCtx->height;
                // 向文件写入一个数据块
                fwrite(pFrameYUV->data[0], 1, y_size, fp_yuv);        //Y
                fwrite(pFrameYUV->data[1], 1, y_size / 4, fp_yuv);  //U
                fwrite(pFrameYUV->data[2], 1, y_size / 4, fp_yuv);  //V

                Frame2JPG(*packet, pFrameYUV,packet->stream_index,pCodecCtx->width, pCodecCtx->height);
                //printf("Succeed to decode 1 frame!\n");
            }
        }
        av_free_packet(packet);
    }

    //flush decoder
    //FIX: Flush Frames remained in Codec
    while (1)
    {
        ret = avcodec_decode_video2(pCodecCtx, pFrame, &got_picture, packet);
        if (ret < 0)
            break;
        if (!got_picture)
            break;
        sws_scale(img_convert_ctx, (const uint8_t* const*)pFrame->data, pFrame->linesize, 0, pCodecCtx->height,
                  pFrameYUV->data, pFrameYUV->linesize);

        int y_size = pCodecCtx->width*pCodecCtx->height;

        fwrite(pFrameYUV->data[0], 1, y_size, fp_yuv);        //Y
        fwrite(pFrameYUV->data[1], 1, y_size / 4, fp_yuv);  //U
        fwrite(pFrameYUV->data[2], 1, y_size / 4, fp_yuv);  //V


        //printf("Flush Decoder: Succeed to decode 1 frame!\n");
    }

    sws_freeContext(img_convert_ctx);
    fclose(fp_yuv);
    av_frame_free(&pFrameYUV);
    av_frame_free(&pFrame);
    avcodec_close(pCodecCtx);
    avformat_close_input(&pFormatCtx);

    return 0;
}

int main()
{
    char filepath[] = "1.mp4";
    decode_h264(filepath);
    return 0;
}
ffmpeg 把视频解码成jpg

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