FFmpeg添加滤镜调整视频对比度和亮度

目的:调整视频的亮度和对比度。
可参考ffmpeg的源码：
\examples\filtering_video.c，视频滤波例子
\libavfilter\vf_eq.c，亮度对比度调整的具体实现
先使用ffmpeg.exe试试效果，女神的原始视频图片：

ffmpeg.exe -i record.mp4 -vf eq=contrast=1:brightness=-0.2 output.mp4 处理后图片

ffmpeg.exe -i record.mp4 -vf eq=contrast=1:brightness=0.2 output.mp4 处理后图片

效果还可以.

写好了，贴代码，主要是参考这个文件\examples\filtering_video.c，C代码改C#遇到了几个坑花了大半天时间

Init函数的contrast和brightness参数分别对应对比度和亮度，取值1-9，5为原始图像。

public unsafe class VideoFiltering
{
    #region 类成员变量
    AVFilterGraph* m_filter_graph = null;
    AVFilterContext* m_buffersink_ctx = null;
    AVFilterContext* m_buffersrc_ctx = null;
    AVFrame* m_filt_frame = null;
    Object m_lock_record = new Object();
    #endregion
    public int Init(int width, int height, int contrast, int brightness)
    {
        lock (m_lock_record)
        {
            // Critical code section
            if (m_filter_graph != null)
                return -1;
            contrast = contrast < 1 ? 1 : contrast;
            contrast = contrast > 9 ? 9 : contrast;
            brightness = brightness < 1 ? 1 : brightness;
            brightness = brightness > 9 ? 9 : brightness;
            float contrast_f = 1 + ((float)(contrast - 5)) / 10;
            float brightness_f = 0 + ((float)(brightness - 5)) / 10;
            string filters_descr = string.Format("eq=contrast=" + contrast_f.ToString() + ":brightness=" + brightness_f.ToString());
            return init_filters(width, height, filters_descr);
        }
   }
    public int Reset(int width, int height, int contrast, int brightness)
    {
        Deinit();
        return Init(width, height, contrast, brightness);
    }
    public int Filter(AVFrame * frame_src, AVFrame **frame_dst)
    {
        lock (m_lock_record)
        {
            *frame_dst = frame_src;
            if (m_filter_graph == null)
            {
                return -1;
            }
            int ret;
            //AV_BUFFERSRC_FLAG_KEEP_REF = 8,
            ret = ffmpeg.av_buffersrc_add_frame_flags(m_buffersrc_ctx, frame_src, 8);
            if (ret < 0)
                return ret;
            ret = ffmpeg.av_buffersink_get_frame(m_buffersink_ctx, m_filt_frame);
            if (ret < 0)
                return ret;
            *frame_dst = m_filt_frame;
            return 0;
        }
    }
    public void UnrefFrame()
    {
        lock (m_lock_record)
        {
            if (m_filter_graph == null)
                return ;
            ffmpeg.av_frame_unref(m_filt_frame);
        }
    }
    public void Deinit()
    {
        if (m_filter_graph == null)
            return ;
        if(m_filter_graph != null)
        {
            fixed(AVFilterGraph** filter_graph = &m_filter_graph)
                ffmpeg.avfilter_graph_free(filter_graph);
        }
        if (m_filt_frame != null)
        {
            fixed (AVFrame** filt_frame = &m_filt_frame)
                ffmpeg.av_frame_free(filt_frame);
        }
    }
    private int init_filters(int width, int height, string filters_descr)
    {
        int ret = 0;
        ffmpeg.avfilter_register_all();
        //AVPixelFormat.AV_PIX_FMT_YUV420P = 0;
        string args = string.Format("video_size=" + width.ToString() + "x" + height.ToString() +
                                    ":pix_fmt=0:time_base=1/20");
        AVFilter* buffersrc = ffmpeg.avfilter_get_by_name("buffer");
        AVFilter* buffersink = ffmpeg.avfilter_get_by_name("buffersink");
        AVFilterInOut* outputs = ffmpeg.avfilter_inout_alloc();
        AVFilterInOut* inputs = ffmpeg.avfilter_inout_alloc();
        //AVRational time_base;
        int* pix_fmts = (int*)ffmpeg.av_malloc(8);
        pix_fmts[0] = (int)AVPixelFormat.AV_PIX_FMT_YUV420P;
        pix_fmts[1] = (int)AVPixelFormat.AV_PIX_FMT_NONE;
        //AVPixelFormat pix_fmts[] = { AVPixelFormat.AV_PIX_FMT_YUV420P, AVPixelFormat.AV_PIX_FMT_NONE };
        m_filter_graph = ffmpeg.avfilter_graph_alloc();
        if(outputs == null || inputs == null || m_filter_graph == null)
        {
            ret = -1;
            goto end;
        }
        fixed (AVFilterContext** buffersrc_ctx = &m_buffersrc_ctx)
        {
            ret = ffmpeg.avfilter_graph_create_filter(buffersrc_ctx, buffersrc, "in", args, null, m_filter_graph);
            if (ret < 0)
            {
                goto end;
            }
        }
        fixed (AVFilterContext** buffersink_ctx = &m_buffersink_ctx)
        {
            ret = ffmpeg.avfilter_graph_create_filter(buffersink_ctx, buffersink, "out", null, null, m_filter_graph);
            if (ret < 0)
            {
                goto end;
            }
        }
        int size = (int)ffmpeg.av_int_list_length_for_size(1, (void*)pix_fmts, unchecked((ulong)AVPixelFormat.AV_PIX_FMT_NONE));
        ret = ffmpeg.av_opt_set_bin(m_buffersink_ctx, "pix_fmts", (byte*)pix_fmts, size, ffmpeg.AV_OPT_SEARCH_CHILDREN);
        if(ret < 0)
            goto end;
        outputs->name = ffmpeg.av_strdup("in");
        outputs->filter_ctx = m_buffersrc_ctx;
        outputs->pad_idx = 0;
        outputs->next = null;
        inputs->name = ffmpeg.av_strdup("out");
        inputs->filter_ctx = m_buffersink_ctx;
        inputs->pad_idx = 0;
        inputs->next = null;
        ret = ffmpeg.avfilter_graph_parse_ptr(m_filter_graph, filters_descr, &inputs, &outputs, null);
        if (ret < 0)
            goto end;
        ret = ffmpeg.avfilter_graph_config(m_filter_graph, null);
        if (ret < 0)
            goto end;
        m_filt_frame = ffmpeg.av_frame_alloc();
        end:
        ffmpeg.avfilter_inout_free(&inputs);
        ffmpeg.avfilter_inout_free(&outputs);
        ffmpeg.av_free(pix_fmts);
        if (ret < 0)
            Deinit();
        return ret;
    }
}

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