ffmpeg 使用濾鏡

ffmpeg 中濾鏡的實現其實並不高明，但是功能強大，先給出過濾鏡的代碼，再翻譯我認爲有的玩的濾鏡。

一幀通過濾鏡的函數：

int Filter_One_Frame(FilterArgs *filter_args,AVFrame *frame, AVFrame *filt_frame,const char * filter_descr)
{
    int ret;
    avcodec_register_all();
    av_register_all();
    avfilter_register_all();//註冊，假如沒有調用會報出不能創建濾鏡鏈

    if (filter_args == NULL || filter_descr == NULL ||frame == NULL ||filt_frame == NULL )
    {
        printf("%s\nLine %d:%s : input_mp4 == NULL or filter_descr == NULL\n", __FILE__, __LINE__,__func__);
         goto end;
    }
    if ((ret = init_filters(filter_descr,filter_args)) < 0)//初始化濾鏡鏈
        goto end;

        frame->pts = av_frame_get_best_effort_timestamp(frame);
        /* push the decoded frame into the filtergraph */
        if (av_buffersrc_add_frame(buffersrc_ctx, frame) < 0)
    {
                av_log(NULL, AV_LOG_ERROR, "Error while feeding the filtergraph\n");
            goto end;
    }
        /* pull filtered pictures from the filtergraph */
     while (1)
    {
                ret = av_buffersink_get_frame(buffersink_ctx, filt_frame);//過濾鏡
                if (ret == AVERROR(EAGAIN) || ret == AVERROR_EOF)
                    break;
                if (ret < 0)
                    goto end;
       }
     ret = 0;
end:

    if (filter_graph != NULL)
        avfilter_graph_free(&filter_graph);//釋放
    if (ret < 0 && ret != AVERROR_EOF) {
        char buf[1024];
        av_strerror(ret, buf, sizeof(buf));
        fprintf(stderr, "Error occurred: %s\n", buf);
        return -1;
    }
        return 0;
}

FilterArgs 一個結構體：

typedef struct Filter_Args
{
    int width;
    int height;
     enum AVPixelFormat pix_fmt;
    AVRational time_base;
    AVRational sample_aspect_ratio;
}FilterArgs;

這些參數在創建濾鏡得時候比較重要，假如和過濾鏡得幀不符和，或者參數不合法會導致通過濾鏡失敗。假如幀的yuv不是從視頻中解碼出來，也就是沒有time_base 和sample_aspect_ratio，那麼我一般會設置成{1,20};

函數init_filters:

int init_filters(const char *filters_descr,FilterArgs *filter_args)

{

    char args[512];

    int ret = 0;

    AVFilter *buffersrc  = avfilter_get_by_name("buffer");
    AVFilter *buffersink = avfilter_get_by_name("buffersink");
    AVFilterInOut *outputs = avfilter_inout_alloc();
    AVFilterInOut *inputs  = avfilter_inout_alloc();

    enum AVPixelFormat pix_fmts[] = {AV_PIX_FMT_YUV420P, AV_PIX_FMT_NONE };//modify by elesos.com ?OEAE????oe??????
    if (filters_descr == NULL )
    {
        printf("%s\nLine %d:%s : filter_args == NULL or filter_descr == NULL\n", __FILE__, __LINE__,__func__);
         goto end;
    }
    filter_graph = avfilter_graph_alloc();
    if (!outputs || !inputs || !filter_graph )
    {
        ret = AVERROR(ENOMEM);
        goto end;
    }
    /* buffer video source: the decoded frames from the decoder will be inserted here. */
    if (filter_args)
    {
          snprintf(args, sizeof(args),
                    "video_size=%dx%d:pix_fmt=%d:time_base=%d/%d:pixel_aspect=%d/%d",
                    filter_args->width, filter_args->height, filter_args->pix_fmt,
                    filter_args->time_base.num, filter_args->time_base.den,
                    filter_args->sample_aspect_ratio.num, filter_args->sample_aspect_ratio.den);
    }
    else
    {
          snprintf(args, sizeof(args),
                    "video_size=%dx%d:pix_fmt=%d:time_base=%d/%d:pixel_aspect=%d/%d",
                    pCodecCtx->width, pCodecCtx->height, pCodecCtx->pix_fmt,
                    pCodecCtx->time_base.num, pCodecCtx->time_base.den,
                    pCodecCtx->sample_aspect_ratio.num, pCodecCtx->sample_aspect_ratio.den);
    }
    puts(args);
    ret = avfilter_graph_create_filter(&buffersrc_ctx, buffersrc, "in",

                                       args, NULL, filter_graph);
    if (ret < 0) {

        av_log(NULL, AV_LOG_ERROR, "Cannot create buffer source\n");

        goto end;

    }
     /* buffer video sink: to terminate the filter chain. */
    ret = avfilter_graph_create_filter(&buffersink_ctx, buffersink, "out",
                                     NULL, NULL, filter_graph);
    if (ret < 0) {
        av_log(NULL, AV_LOG_ERROR, "Cannot create buffer sink\n");
        goto end;

    }
    ret = av_opt_set_int_list(buffersink_ctx, "pix_fmts", pix_fmts,AV_PIX_FMT_NONE, AV_OPT_SEARCH_CHILDREN);
    if (ret < 0) {
        av_log(NULL, AV_LOG_ERROR, "Cannot set output pixel format\n");
        goto end;
    }

    /* Endpoints for the filter graph. */
    outputs->name       = av_strdup("in");
    outputs->filter_ctx = buffersrc_ctx;
    outputs->pad_idx    = 0;
    outputs->next       = NULL;

    inputs->name       = av_strdup("out");
    inputs->filter_ctx = buffersink_ctx;
    inputs->pad_idx    = 0;
    inputs->next       = NULL;

    if ((ret = avfilter_graph_parse_ptr(filter_graph, filters_descr,&inputs, &outputs, NULL)) < 0)
              goto end;

    if ((ret = avfilter_graph_config(filter_graph, NULL)) < 0)

        goto end;
    end:
    avfilter_inout_free(&inputs);
    avfilter_inout_free(&outputs);
    return ret;

}