三.ffmpeg对yuv的操作

一.windows

1.使用ffmpeg录制mp4视频

cpp 复制代码

#获取音视频设备
ffmpeg -list_devices true -f dshow -i dummy
#录制视频
ffmpeg -f dshow -i video="xxxx" -c"v libx264 -pix_fmt yuv420p output.mp4

2.将mp4转换为yuv数据

cpp 复制代码

//-i：输入文件选项；-an：不处理音频流；
//-c:v rawvideo 视频编码器的选项，使用原始视频格式进行编码（不进行压缩）；
//-pix_fmt yuv420p:输出视频的像素格式
ffmpeg -i output.mp4 -an -c:v rawvideo -pix_fmt yuv420p out.yuv
//播放
ffplay -f rawvideo -pixel_format yuv420p -video_size 1280x720 out1.yuv

3.也可以单独播放单独分量

cpp 复制代码

//播放yuv数据
ffplay -s 1280x720 -vf extractplanes='y' out.yuv
//提取yuv三个分量为三个文件
ffmpeg -s 1280x720 -pix_fmt yuv420p -i out.yuv -filter_complex "extractplanes=y+u+v[y][u][v]" -map "[y]" y.yuv -map "[u]" u.yuv -map "[v]" v.yuv
//播放单个分量 格式为gray
ffplay -s 1280x720 -pix_fmt gray y.yuv

播放出来y、u、v都是没有颜色的，为什么u和v表示蓝色和红色的差分量也没有颜色呢？

因为u和v分量的值是相对于y分量的，没有y分量它们都无法提供完整的颜色信息。

4.api调用

cpp 复制代码

#可以查看摄像头输出的视频数据的编码格式和像素格式
ffmpeg -f dshow -i "Integrated Camera" -vcodec copy -f null -

5.整体代码

cpp 复制代码

int read_video()
{
    int ret = 0;
    char errors[1024];
    AVFormatContext *fmt_ctx = NULL;
    AVDictionary *options = NULL;
    AVAudioFifo *fifo = nullptr;
    // FILE *outfile = fopen("./out.yuv", "wb+");
    FILE *outfile_yuv = fopen("./out1.yuv", "wb+");
    if (outfile_yuv == nullptr)
    {
        printf("filed open out file\n");
    }

    AVPacket pkt;
    av_init_packet(&pkt);
    int frame_count = 0;

    // 找到采集工具
    const AVInputFormat *iformat = av_find_input_format("dshow");
    if (iformat == NULL)
    {
        printf("AVInputFormat find failed \n");
        return -1;
    }

    // 打开视频设备
    av_dict_set(&options, "video_size", "1280x720", 0);
    av_dict_set(&options, "framerate", "30", 0);
    // av_dict_set(&options, "pixel_format", "yuv420p", 0);
    ret = open_dev(&fmt_ctx, "video=Integrated Camera", iformat, &options);

    AVCodecContext *codec_ctx;
    // 找到视频流
    int video_stream_index = -1;
    for (int i = 0; i < fmt_ctx->nb_streams; i++)
    {
        if (fmt_ctx->streams[i]->codecpar->codec_type == AVMEDIA_TYPE_VIDEO)
        {
            video_stream_index = i;
            break;
        }
    }

    // 获取解码器
    AVCodecParameters *codecpar = fmt_ctx->streams[video_stream_index]->codecpar;
    // AVCodecID
    printf("codecParameters:%d , AVCodecID : %d \n", codecpar->format, codecpar->codec_id);
    const AVCodec *codec = avcodec_find_decoder(codecpar->codec_id);
    codec_ctx = avcodec_alloc_context3(codec);
    avcodec_parameters_to_context(codec_ctx, codecpar);
    if (avcodec_open2(codec_ctx, codec, NULL) < 0)
    {
        fprintf(stderr, "Could not open codec\n");
        avformat_close_input(&fmt_ctx);
        return -1;
    }
    // 初始化格式转换上下文
    struct SwsContext *sws_ctx = sws_getContext(
        1280, 720, AV_PIX_FMT_YUVJ422P, // 输入图像的宽度、高度和像素格式
        1280, 720, AV_PIX_FMT_YUV420P,  // 输出图像的宽度、高度和像素格式
        SWS_BILINEAR,                   // 转换算法
        NULL, NULL, NULL                // 额外参数
    );
    int count = 0;

    static bool finished = false;
    AVFrame *frame = av_frame_alloc();
    AVFrame *outFrame = av_frame_alloc();
    // 设置 YUV 422P 帧
    frame->format = AV_PIX_FMT_YUV422P;
    frame->width = 1280;
    frame->height = 720;
    // 设置 YUV 420P 帧
    outFrame->format = AV_PIX_FMT_YUV420P;
    outFrame->width = 1280;
    outFrame->height = 720;

    // 分配数据
    int ret420 = av_image_alloc(outFrame->data, outFrame->linesize, 1280, 720, AV_PIX_FMT_YUV420P, 1);
    if (ret420 < 0)
    {
        fprintf(stderr, "无法分配图像数据\n");
        return -1;
    }
    // AVPixelFormat;
    av_dump_format(fmt_ctx, 0, "video=Integrated Camera", 0);
    // 读取数据包并解码
    size_t written_y = 0, written_u = 0, written_v = 0;
    while (av_read_frame(fmt_ctx, &pkt) >= 0)
    {
        ret = avcodec_send_packet(codec_ctx, &pkt);
        if (ret < 0)
        {
            fprintf(stderr, "Error sending packet to decoder: %s\n", av_err2str(ret));
            av_packet_unref(&pkt);
            continue; // 继续处理下一个数据包
        }
        while (avcodec_receive_frame(codec_ctx, frame) >= 0)
        {
            sws_scale(sws_ctx, frame->data, frame->linesize, 0, 720, outFrame->data, outFrame->linesize);

            // // 计算 YUV 数据大小
            int size_y = outFrame->width * outFrame->height;
            int size_u = (outFrame->width / 2) * (outFrame->height);
            int size_v = (outFrame->width / 2) * (outFrame->height);
            int total_size = size_y + size_u + size_v;

            printf("%d Frame-format %d: Y size = %d, U size = %d, V size = %d, Total size = %d\n", count,
                   outFrame->format, size_y, size_u, size_v, total_size);
            // 将解码后的 YUV 数据写入文件
            written_y = fwrite(outFrame->data[0], 1, size_y, outfile_yuv); // Y
            fflush(outfile_yuv);
            written_u = fwrite(outFrame->data[1], 1, size_u, outfile_yuv); // U
            fflush(outfile_yuv);
            written_v = fwrite(outFrame->data[2], 1, size_v, outfile_yuv); // V
            fflush(outfile_yuv);
        }
        av_packet_unref(&pkt);
        if (count++ > 50)
            break;
    }
    // 发送结束信号
    avcodec_send_packet(codec_ctx, NULL);
    while (avcodec_receive_frame(codec_ctx, outFrame) >= 0)
    {
        printf("get one frame %d ,frame_w:%d,frame_h:%d\n", count, outFrame->width, outFrame->height);
        fwrite(frame->data[0], 1, outFrame->width * outFrame->height, outfile_yuv);         // Y
        fwrite(frame->data[1], 1, (outFrame->width / 2) * (outFrame->height), outfile_yuv); // U
        fwrite(frame->data[2], 1, (outFrame->width / 2) * (outFrame->height), outfile_yuv); // V
        fflush(outfile_yuv);
        count++;
    }
    av_frame_free(&frame);
    avcodec_free_context(&codec_ctx);

    avformat_close_input(&fmt_ctx);
    fclose(outfile_yuv);
    av_log(NULL, AV_LOG_DEBUG, "end");

    return 0;
}

6.遇到问题

1.通过av_read_frame获取到的视频数据不是yuv420p的原始数据，而是通过mjpeg编码的yuv422p的数据。