无法解析变量PIX_FMT_RGB24，使用最新版本安装ffmpeg源代码

Question

我根据https://trac.ffmpeg.org/wiki/CompilationGuide/Ubuntu从源代码安装了ffmpeg ，并编写了一个测试文件来保存视频中的ppm文件，但代码无法reslove PIX_FMT_RGB24，我编写的代码如下：

int main() {
    // Initalizing these to NULL prevents segfaults!
    AVFormatContext   *pFormatCtx = NULL;
    int               i, videoStream;
    AVCodecContext    *pCodecCtxOrig = NULL;
    AVCodecContext    *pCodecCtx = NULL;
    AVCodec           *pCodec = NULL;
    AVFrame           *pFrame = NULL;
    AVFrame           *pFrameRGB = NULL;
    AVPacket          packet;
    int               frameFinished;
    int               numBytes;
    uint8_t           *buffer = NULL;
    struct SwsContext *sws_ctx = NULL;

    const char* url = "/home/liulijuan/bin/test.mp4";

    // [1] Register all formats and codecs
    av_register_all();

    // [2] Open video file
    if(avformat_open_input(&pFormatCtx, url, NULL, NULL)!=0)
        return -1; // Couldn't open file

    // [3] Retrieve stream information
    if(avformat_find_stream_info(pFormatCtx, NULL)<0)
        return -1; // Couldn't find stream information

    // Dump information about file onto standard error
    av_dump_format(pFormatCtx, 0, url, 0);

    // Find the first video stream
    videoStream=-1;
    for(i=0; i<pFormatCtx->nb_streams; i++)
        if(pFormatCtx->streams[i]->codec->codec_type==AVMEDIA_TYPE_VIDEO) {
            videoStream=i;
            break;
        }
    if(videoStream==-1)
        return -1; // Didn't find a video stream

    // Get a pointer to the codec context for the video stream
    pCodecCtxOrig=pFormatCtx->streams[videoStream]->codec;
    // Find the decoder for the video stream
    pCodec=avcodec_find_decoder(pCodecCtxOrig->codec_id);
    if(pCodec==NULL) {
        fprintf(stderr, "Unsupported codec!\n");
        return -1; // Codec not found
    }
    // Copy context
    pCodecCtx = avcodec_alloc_context3(pCodec);
    if(avcodec_copy_context(pCodecCtx, pCodecCtxOrig) != 0) {
        fprintf(stderr, "Couldn't copy codec context");
        return -1; // Error copying codec context
    }

    // Open codec
    if(avcodec_open2(pCodecCtx, pCodec, NULL)<0)
        return -1; // Could not open codec

    // Allocate video frame
    pFrame=av_frame_alloc();

    // Allocate an AVFrame structure
    pFrameRGB=av_frame_alloc();
    if(pFrameRGB==NULL)
        return -1;

    // Determine required buffer size and allocate buffer
    numBytes=avpicture_get_size(PIX_FMT_RGB24, pCodecCtx->width,
                                pCodecCtx->height);
    buffer=(uint8_t *)av_malloc(numBytes*sizeof(uint8_t));

    // Assign appropriate parts of buffer to image planes in pFrameRGB
    // Note that pFrameRGB is an AVFrame, but AVFrame is a superset
    // of AVPicture
    avpicture_fill((AVPicture *)pFrameRGB, buffer, PIX_FMT_RGB24,
                   pCodecCtx->width, pCodecCtx->height);

    // initialize SWS context for software scaling
    sws_ctx = sws_getContext(pCodecCtx->width,
                             pCodecCtx->height,
                             pCodecCtx->pix_fmt,
                             pCodecCtx->width,
                             pCodecCtx->height,
                             PIX_FMT_RGB24,
                             SWS_BILINEAR,
                             NULL,
                             NULL,
                             NULL
    );

    // [4] Read frames and save first five frames to disk
    i=0;
    while(av_read_frame(pFormatCtx, &packet)>=0) {
        // Is this a packet from the video stream?
        if(packet.stream_index==videoStream) {
            // Decode video frame
            avcodec_decode_video2(pCodecCtx, pFrame, &frameFinished, &packet);

            // Did we get a video frame?
            if(frameFinished) {
                // Convert the image from its native format to RGB
                sws_scale(sws_ctx, (uint8_t const * const *)pFrame->data,
                          pFrame->linesize, 0, pCodecCtx->height,
                          pFrameRGB->data, pFrameRGB->linesize);

                // Save the frame to disk
                if(++i<=5)
                    SaveFrame(pFrameRGB, pCodecCtx->width, pCodecCtx->height,
                              i);
            }
        }

        // Free the packet that was allocated by av_read_frame
        av_free_packet(&packet);
    }

    // Free the RGB image
    av_free(buffer);
    av_frame_free(&pFrameRGB);

    // Free the YUV frame
    av_frame_free(&pFrame);

    // Close the codecs
    avcodec_close(pCodecCtx);
    avcodec_close(pCodecCtxOrig);

    // Close the video file
    avformat_close_input(&pFormatCtx);

    return 0;
}

所以我替换PIX_FMT_RGB24为AV_PIX_FMT_RGB24，但我无法打开保存的ppm文件，保存代码如下：

void SaveFrame(AVFrame *pFrame, int width, int height, int iFrame) {
    FILE *pFile;
    char szFilename[32];
    int  y;

    printf("start save frame ...\n");
    // Open file
    sprintf(szFilename, "/home/liulijuan/frame%d.ppm", iFrame);
    pFile=fopen(szFilename, "wb");
    if(pFile==NULL)
        return;

    printf("start write header ...\n");
    // Write header
    fprintf(pFile, "/P6\n%d %d\n255\n", width, height);

    // Write pixel data
    for(y=0; y<height; y++)
        fwrite(pFrame->data[0]+y*pFrame->linesize[0], 1, width*3, pFile);

    // Close file
    fclose(pFile);
    printf("close file ...\n");
}

那么，这段代码有什么问题呢？

Answer 1

从提交78071a14开始，像素格式已添加前缀AV_，并且PIX_FMT_*定义已移至libavutil/old_pix_fmts.h（包含在原始版本中pixfmt.h）。该文件随后在下一个主要版本中被删除。

解决方法是将此前缀 ( AV_) 添加到任何PIX_FMT_*尚未更新的语句中。