1.区域视频增强

    FFmpeg滤镜功能十分强大，用滤镜可以实现视频的区域增强功能。

    用eq滤镜就可以实现亮度、对比度、饱和度等的常用视频增强功能。

    推荐两篇写得不错的博文：

        （1）ffmpeg综合应用示例（二）——为直播流添加特效 - 张晖的专栏 - 博客频道 - CSDN.NET；

        （2）ffmpeg 滤镜及其效果 - 党玉涛 - 博客频道 - CSDN.NET

     第（1）篇博客对于如何用代码来写滤镜讲得比较清楚，第（2）篇则列出了许多滤镜写法的例子。

参考第（1）篇博客，滤镜的代码如下：

设置滤镜：

int FFmpeg_filter::apply_filters(AVFormatContext *ifmt_ctx)
{
    char args[512];
    int ret;
    AVFilterInOut *outputs = avfilter_inout_alloc();
    if (!outputs)
    {
        printf("Cannot alloc output\n");
        return -1;
    }
    AVFilterInOut *inputs = avfilter_inout_alloc();
    if (!inputs)
    {
        printf("Cannot alloc input\n");
        return -1;
    }

    AVFilterGraph *filter_graph = NULL;
    if (filter_graph)
        avfilter_graph_free(&filter_graph);
    filter_graph = avfilter_graph_alloc();
    if (!filter_graph)
    {
        printf("Cannot create filter graph\n");
        return -1;
    }

    /* buffer video source: the decoded frames from the decoder will be inserted here. */
    snprintf(args, sizeof(args),
        "video_size=%dx%d:pix_fmt=%d:time_base=%d/%d:pixel_aspect=%d/%d",
        ifmt_ctx->streams[0]->codec->width, ifmt_ctx->streams[0]->codec->height, ifmt_ctx->streams[0]->codec->pix_fmt,
        ifmt_ctx->streams[0]->time_base.num, ifmt_ctx->streams[0]->time_base.den,
        ifmt_ctx->streams[0]->codec->sample_aspect_ratio.num, ifmt_ctx->streams[0]->codec->sample_aspect_ratio.den);

    ret = avfilter_graph_create_filter(&buffersrc_ctx, buffersrc, "in",
        args, NULL, filter_graph);
    if (ret < 0) {
        printf("Cannot create buffer source\n");
        return ret;
    }

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

    /* 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;

    const char *filter_descr = "null";
    const char *filter_mirror = "crop=iw/2:ih:0:0,split[left][tmp];[tmp]hflip[right];[left]pad=iw*2[a];[a][right]overlay=w";
    const char *filter_watermark = "movie=logo.png[wm];[in][wm]overlay=5:5[out]";
    const char *filter_negate = "negate[out]";
    const char *filter_edge = "edgedetect[out]";
    const char *filter_split4 = "scale=iw/2:ih/2[in_tmp];[in_tmp]split=4[in_1][in_2][in_3][in_4];[in_1]pad=iw*2:ih*2[a];[a][in_2]overlay=w[b];[b][in_3]overlay=0:h[d];[d][in_4]overlay=w:h[out]";
    const char *filter_vintage = "curves=vintage";
    const char *filter_brightness = "eq=brightness=0.5[out] ";    //亮度。The value must be a float value in range -1.0 to 1.0. The default value is "0". 
    const char *filter_contrast = "eq=contrast=1.5[o