如何在ffmpeg中添加一个简单的filter

矫情吗；* 2023-02-17 14:55 90阅读 0赞

# 如何在ffmpeg中添加一个简单的filter #

### 文章目录 ###

*  如何在ffmpeg中添加一个简单的filter
 *   *  filter大体写法
     *  yuv模型
     *  测试
     *  graph dump

--------------------

大体步骤如下:

1. 编写filter文件, 比如vf_xxx.c, 放在libavfilter目录下
    2. 在libavfilter/allfilters.c  +++  extern AVFilter ff_vf_xxx
    3. 修改libavfilter/Makefile    +++  OBJS-$(CONFIG_XXX_FILTER) += vf_xxx.o
    4. 修改ffbuild/config.mak      +++  CONFIG_XXX_FILTER=yes

## filter大体写法 ##

一个filter的定义了不少回调,不过一个简洁的也许你只需要写init(),uinit(),query\_format()即可. filter会在config\_graph()的时候初始化整个滤镜链图,这里会调用filter的init()和query\_format(),add\_buffersrc()会激活滤镜链图,使frame在滤镜链图中各种filter回调中进行处理.

pad -link-> filter -link-> pad -link->....
    pad -link-|       |-link-> pad -link->
       ....              ....

int (*preinit)(AVFilterContext *ctx);
    
        int (*init)(AVFilterContext *ctx);
    
        int (*init_dict)(AVFilterContext *ctx, AVDictionary **options);
     
        void (*uninit)(AVFilterContext *ctx);
    
        int (*query_formats)(AVFilterContext *);
    
        int (*process_command)(AVFilterContext *, const char *cmd, const char *arg, char *res, int res_len, int flags);
    
        int (*init_opaque)(AVFilterContext *ctx, void *opaque);
    
        int (*activate)(AVFilterContext *ctx);

编写一个vf\_yuvy.c file 我们进行一个frame yuv 分量的提取测试.

## yuv模型 ##

这个颜色模型使用 Y 来表示亮度，还有两种颜色通道：Cb（蓝色色度） 和 Cr（红色色度）。YCbCr 可以由 RGB 转换得来，也可以转换回 RGB。使用这个模型我们可以创建拥有完整色彩的图像

YCbCr 和 RGB 之间的转换公式

Y = 0.299R + 0.587G + 0.114B
    一旦我们有了亮度后，我们就可以拆分颜色（蓝色色度和红色色度）：
    
    Cb = 0.564(B - Y)
    Cr = 0.713(R - Y)
    
    # 并且我们也可以使用 YCbCr 转换回来，甚至得到绿色。
    R = Y + 1.402Cr
    B = Y + 1.772Cb
    G = Y - 0.344Cb - 0.714Cr

省略实现,大体写法如下:

#include <string.h>
    
    #include "libavutil/internal.h"
    #include "libavutil/mem.h"
    #include "libavutil/opt.h"
    
    #include "avfilter.h"
    #include "formats.h"
    #include "internal.h"
    #include "video.h"
    
    typedef struct YUVYContext {
        
        const AVClass *class;
        char *yuv;
    
        enum AVPixelFormat *formats;
    } YUVYContext;
    
    static av_cold int init(AVFilterContext *ctx)
    {
        
        YUVYContext *s = ctx->priv;
    
        ...
    
        return 0;
    }
    
    static av_cold void uninit(AVFilterContext *ctx)
    {
        
        ...
    }
    
    //定义此filter在其输入输出所支持的format, 一般在filter初始化后调用,此callback必须设置AVFilterLink.out_formats
    static int query_formats(AVFilterContext *ctx)
    {
        
        static const enum AVPixelFormat pix_fmts[] = {
        
            AV_PIX_FMT_YUV420P, AV_PIX_FMT_NONE
        };
    
        AVFilterFormats *fmts_list = ff_make_format_list(pix_fmts);
        if (!fmts_list)
            return AVERROR(ENOMEM);
        return ff_set_common_formats(ctx, fmts_list);
    }
    
    static int cnt = 0;
    static int filter_frame(AVFilterLink *link, AVFrame *in)
    {
        
        YUVYContext *yuvy = link->dst->priv;
        int i;
        AVFilterLink *olink = link->dst->outputs[0];
        AVFrame *out = av_frame_alloc();
        out->width   = in->width;
        out->height  = in->height;
        out->format  = in->format;
    
        out = ff_get_video_buffer(olink, olink->w, olink->h);
        if (!out) {
        
            av_frame_free(&in);
            return AVERROR(ENOMEM);
        }
        av_frame_copy_props(out, in);
        av_frame_copy(out, in);
    
        //av_log(link->dst, AV_LOG_INFO, "filter_frame %d.\n", cnt++);
        if (yuvy->yuv[0] == 'y') {
        
            ...
    
        } else if (yuvy->yuv[0] == 'u' && yuvy->yuv[1] == 'v') {
        
            ...
        } else if (yuvy->yuv[0] == 'b') {
        
            ...
        } else if (yuvy->yuv[0] == 'u') {
        
            ...
        } else if (yuvy->yuv[0] == 'v') {
        
            ...
        }
    
        return ff_filter_frame(olink, out);
    }
    
    static int config_props(AVFilterLink *outlink)
    {
        
        ...
    }
    
    #define OFFSET(x) offsetof(YUVYContext, x)
    static const AVOption options[] = {
        
        {
         "yuv", "Y|G|R|B", OFFSET(yuv), AV_OPT_TYPE_STRING, .flags = AV_OPT_FLAG_VIDEO_PARAM | AV_OPT_FLAG_FILTERING_PARAM },
        {
         NULL }
    };
    
    #define CONFIG_YUVY_FILTER 1
    #if CONFIG_YUVY_FILTER
    
    #define yuvy_options options
    AVFILTER_DEFINE_CLASS(yuvy);
    
    static const AVFilterPad avfilter_vf_yuvy_inputs[] = {
        
        {
        
            .name             = "default",
            .type             = AVMEDIA_TYPE_VIDEO,
            .filter_frame     = filter_frame,
        },
        {
         NULL }
    };
    
    static const AVFilterPad avfilter_vf_yuvy_outputs[] = {
        
        {
        
            .name         = "default",
            .type         = AVMEDIA_TYPE_VIDEO,
            .config_props = config_props,
        },
        {
         NULL }
    };
    
    AVFilter ff_vf_yuvy = {
        
        .name          = "yuvy",
        .description   = NULL_IF_CONFIG_SMALL("Convert the input video of yuv420p pixel format to Y|R|G|B graph"),
    
        .init          = init,
        .uninit        = uninit,
    
        .query_formats = query_formats,
    
        .priv_size     = sizeof(YUVYContext),
        .priv_class    = &yuvy_class,
    
        .inputs        = avfilter_vf_yuvy_inputs,
        .outputs       = avfilter_vf_yuvy_outputs,
    };
    #endif /* CONFIG_YUVY_FILTER */

## 测试 ##

ffmpeg -y -i demo.mp4 -vf "yuvy=yuv=y" -c:v libx264 -qp 0  y.mp4
    ffmpeg -y -i demo.mp4 -vf "yuvy=yuv=u" -c:v libx264 -qp 0  u.mp4
    ffmpeg -y -i demo.mp4 -vf "yuvy=yuv=v" -c:v libx264 -qp 0  v.mp4
    ffmpeg -y -i demo.mp4 -vf "yuvy=yuv=uv" -c:v libx264 -qp 0  uv.mp4
    ffmpeg -y -i demo.mp4 -vf "yuvy=yuv=b" -c:v libx264 -qp 0  b.mp4

![在这里插入图片描述][watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3FxXzE3MzA4MzIx_size_16_color_FFFFFF_t_70]

ffmpeg -y -i demo.jpeg -vf "yuvy=yuv=y" y.jpeg; \
    ffmpeg -y -i demo.jpeg -vf "yuvy=yuv=u" u.jpeg; \
    ffmpeg -y -i demo.jpeg -vf "yuvy=yuv=v" v.jpeg; \
    ffmpeg -y -i demo.jpeg -vf "yuvy=yuv=uv" uv.jpeg; \
    ffmpeg -y -i demo.jpeg -vf "yuvy=yuv=b" b.jpeg

## graph dump ##

可以看到在部分输入像素格式不受支持的时候,ffmpeg会自动加一个auto\_scale 转换了format.

+---------------+
    graph 0 input from stream 0:0:default--[1920x1080 1:1 yuv420p]--default| Parsed_yuvy_0 |default--[1920x1080 1:1 yuv420p]--format:default
                                                                           |    (yuvy)     |
                                                                           +---------------+
    
    +-------------------------------+
    | graph 0 input from stream 0:0 |default--[1920x1080 1:1 yuv420p]--Parsed_yuvy_0:default
    |           (buffer)            |
    +-------------------------------+
    
                                                    +--------------+
    format:default--[1920x1080 1:1 yuv420p]--default|   out_0_0    |
                                                    | (buffersink) |
                                                    +--------------+
    
                                                           +----------+
    Parsed_yuvy_0:default--[1920x1080 1:1 yuv420p]--default|  format  |default--[1920x1080 1:1 yuv420p]--out_0_0:default
                                                           | (format) |
                                                           +----------+

+---------------+
    auto_scaler_0:default--[1280x720 1:1 yuv420p]--default| Parsed_yuvy_0 |default--[1280x720 1:1 yuv420p]--format:default
                                                          |    (yuvy)     |
                                                          +---------------+
    
    +-------------------------------+
    | graph 0 input from stream 0:0 |default--[1280x720 1:1 yuv444p]--auto_scaler_0:default
    |           (buffer)            |
    +-------------------------------+
    
                                                   +--------------+
    format:default--[1280x720 1:1 yuv420p]--default|   out_0_0    |
                                                   | (buffersink) |
                                                   +--------------+
    
                                                          +----------+
    Parsed_yuvy_0:default--[1280x720 1:1 yuv420p]--default|  format  |default--[1280x720 1:1 yuv420p]--out_0_0:default
                                                          | (format) |
                                                          +----------+
    
                                                                          +---------------+
    graph 0 input from stream 0:0:default--[1280x720 1:1 yuv444p]--default| auto_scaler_0 |default--[1280x720 1:1 yuv420p]--Parsed_yuvy_0:default
                                                                          |    (scale)    |
                                                                          +---------------+

[watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3FxXzE3MzA4MzIx_size_16_color_FFFFFF_t_70]: https://img-blog.csdnimg.cn/20200614190222700.png?x-oss-process=image/watermark,type_ZmFuZ3poZW5naGVpdGk,shadow_10,text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3FxXzE3MzA4MzIx,size_16,color_FFFFFF,t_70