c++ - FFMPEG 错误 : Exactly one scaler algorithm must be chosen

Question

我目前正在从事 FFMPEG 项目。我正在尝试使用此代码将 RGB 图像转换为 YUV 图像(我昨晚在互联网上找到它):

 void Decode::video_encode_example(const char *filename, int codec_id)

    {

    AVCodec *codec;

    AVCodecContext *c= NULL;

    int i, ret, x, y, got_output;
    FILE *f;
    AVFrame *frame;
    AVPacket pkt;
    uint8_t endcode[] = { 0, 0, 1, 0xb7 };

    printf("Encode video file %s\n", filename);

    /* find the mpeg1 video encoder */
    codec = avcodec_find_encoder((enum AVCodecID)codec_id);
    if (!codec) {
        fprintf(stderr, "Codec not found\n");
        exit(1);
    }

    c = avcodec_alloc_context3(codec);
    if (!c) {
        fprintf(stderr, "Could not allocate video codec context\n");
        exit(2);
    }

    /* put sample parameters */
    c->bit_rate = 400000;
    /* resolution must be a multiple of two */
    c->width = 352;
    c->height = 288;
    /* frames per second */
    c->time_base = (AVRational){1,25};
    /* emit one intra frame every ten frames
     * check frame pict_type before passing frame
     * to encoder, if frame->pict_type is AV_PICTURE_TYPE_I
     * then gop_size is ignored and the output of encoder
     * will always be I frame irrespective to gop_size
     */
    c->gop_size = 10;
    c->max_b_frames = 1;
    c->pix_fmt = AV_PIX_FMT_YUV420P;

    if (codec_id == AV_CODEC_ID_H264)
        av_opt_set(c->priv_data, "preset", "slow", 0);

    /* open it */
    if (avcodec_open2(c, codec, NULL) < 0) {
        fprintf(stderr, "Could not open codec\n");
        exit(3);
    }

    f = fopen(filename, "wb");
    if (!f) {
        fprintf(stderr, "Could not open %s\n", filename);
        exit(4);
    }

    frame = avcodec_alloc_frame();// Dans une version plus récente c'est av_frame_alloc
    if (!frame) {
        fprintf(stderr, "Could not allocate video frame\n");
        exit(5);
    }
    frame->format = c->pix_fmt;
    frame->width  = c->width;
    frame->height = c->height;

    /* the image can be allocated by any means and av_image_alloc() is
     * just the most convenient way if av_malloc() is to be used */
    ret = av_image_alloc(frame->data, frame->linesize, c->width, c->height,
                         c->pix_fmt, 32);
    if (ret < 0) {
        fprintf(stderr, "Could not allocate raw picture buffer\n");
        exit(6);
    }

    //
    // RGB to YUV:
    //    http://stackoverflow.com/questions/16667687/how-to-convert-rgb-from-yuv420p-for-ffmpeg-encoder
    //
    // Create some dummy RGB "frame"
    uint8_t *rgba32Data = new uint8_t[4*c->width*c->height];

    SwsContext * ctx = sws_getContext(c->width, c->height,
                                      AV_PIX_FMT_RGBA, c->width, c->height,
                                      AV_PIX_FMT_YUV420P, 0, 0, 0, 0);


    /* encode 1 second of video */
    for (i = 0; i < 25; i++) {
        av_init_packet(&pkt);
        pkt.data = NULL;    // packet data will be allocated by the encoder
        pkt.size = 0;


        fflush(stdout);
        /* prepare a dummy image */
        /* Y */
        //        for (y = 0; y < c->height; y++) {
        //            for (x = 0; x < c->width; x++) {
        //                frame->data[0][y * frame->linesize[0] + x] = x + y + i * 3;
        //            }
        //        }
        //
        //        /* Cb and Cr */
        //        for (y = 0; y < c->height/2; y++) {
        //            for (x = 0; x < c->width/2; x++) {
        //                frame->data[1][y * frame->linesize[1] + x] = 128 + y + i * 2;
        //                frame->data[2][y * frame->linesize[2] + x] = 64 + x + i * 5;
        //            }
        //        }

        uint8_t *pos = rgba32Data;
        for (y = 0; y < c->height; y++)
        {
            for (x = 0; x < c->width; x++)
            {
                pos[0] = i / (float)25 * 255;
                pos[1] = 0;
                pos[2] = x / (float)(c->width) * 255;
                pos[3] = 255;
                pos += 4;
            }
        }

        uint8_t * inData[1] = { rgba32Data }; // RGBA32 have one plane
        //
        // NOTE: In a more general setting, the rows of your input image may
        //       be padded; that is, the bytes per row may not be 4 * width.
        //       In such cases, inLineSize should be set to that padded width.
        //
        int inLinesize[1] = { 4*c->width }; // RGBA stride
        sws_scale(ctx, inData, inLinesize, 0, c->height, frame->data, frame->linesize);

        frame->pts = i;

        /* encode the image */
        ret = avcodec_encode_video2(c, &pkt, frame, &got_output);
        if (ret < 0) {
            fprintf(stderr, "Error encoding frame\n");
            exit(7);
        }

        if (got_output) {
            printf("Write frame %3d (size=%5d)\n", i, pkt.size);
            fwrite(pkt.data, 1, pkt.size, f);
            av_free_packet(&pkt);
        }
    }

    /* get the delayed frames */
    for (got_output = 1; got_output; i++) {
        fflush(stdout);

        ret = avcodec_encode_video2(c, &pkt, NULL, &got_output);
        if (ret < 0) {
            fprintf(stderr, "Error encoding frame\n");
            exit(8);
        }

        if (got_output) {
            printf("Write frame %3d (size=%5d)\n", i, pkt.size);
            fwrite(pkt.data, 1, pkt.size, f);
            av_free_packet(&pkt);
        }
    }

    /* add sequence end code to have a real mpeg file */
    fwrite(endcode, 1, sizeof(endcode), f);
    fclose(f);

    avcodec_close(c);
    av_free(c);
    av_freep(&frame->data[0]);
    avcodec_free_frame(&frame);// Dans une version plus récente c'est av_frame_alloc
    printf("\n");
    }

        int main()
        {

            Decode d;

            avcodec_register_all();

            d.video_encode_example("/home/Dave/Desktop/test.mpg",AV_CODEC_ID_MPEG2VIDEO);

        }

当我运行这个应用程序时，我的 Linux 终端显示以下错误:

[swscaler @ 0x1e1dc60] 必须选择一个缩放器算法
段错误(核心已转储)

我不知道实际发生了什么。你能帮帮我吗？

Answer 1

SwsContext * ctx = sws_getContext(c->width, c->height,
                                  AV_PIX_FMT_RGBA, c->width, c->height,
                                  AV_PIX_FMT_YUV420P, 0, 0, 0, 0);

您的“标志”字段(参见 docs - 4 个零列表中的第一个)必须是非零的。有效值为 this page 顶部列表中的 SWS_FAST_BILINEAR - SWS_ERROR_DIFFUSION .一个好的默认设置是只设置缩放算法，并使用例如SWS_BICUBIC作为 bicubic 的值插值。高端缩放算法(如 SPS_SPLINE 用于 spline 插值)的计算量更大，而低端缩放算法(如 SWS_POINT 用于 nearest neighbour 插值)往往看起来更糟，因此您选择的确切值这取决于您愿意花费多少 CPU 与您对最终结果的视觉质量的关心程度。