此前libavfilter一直是结合着libavcodec等类库的接口函数使用的，因此我一直以为libavfilter库与libavcodec等类库是高度耦合的(也就是如果想使用libavfilter的视音频特效功能的话必须使用libavcodec等类库的函数)。这两天空闲的时候研究了一下libavfilter的代码后发现实际情况不是这样的：libavfilter可以独立于libavcodec等类库的接口函数作为一个“纯粹”的视音频特效类库进行使用。本文记录的“纯净版”的avfilter的例子即实现了一个纯粹的视频特效添加的功能。该例子输入为一个YUV文件，输出也是一个YUV文件，通过avfilter的功能可以处理该YUV文件实现去色调、模糊、水平翻转、裁剪、加方框、叠加文字等功能。

流程图

该程序的流程图如下所示。AVFilter的初始化比较复杂，而使用起来比较简单。初始化的时候需要调用avfilter_register_all()到avfilter_graph_config()一系列函数。而使用的时候只有两个函数：av_buffersrc_add_frame()用于向FilterGraph中加入一个AVFrame，而av_buffersink_get_frame()用于从FilterGraph中取出一个AVFrame。

流程中的关键函数如下所示：

avfilter_register_all()：注册所有AVFilter。

avfilter_graph_alloc()：为FilterGraph分配内存。

avfilter_graph_create_filter()：创建并向FilterGraph中添加一个Filter。

avfilter_graph_parse_ptr()：将一串通过字符串描述的Graph添加到FilterGraph中。

avfilter_graph_config()：检查FilterGraph的配置。

av_buffersrc_add_frame()：向FilterGraph中加入一个AVFrame。

av_buffersink_get_frame()：从FilterGraph中取出一个AVFrame。

代码

/**  * 最简单的基于FFmpeg的AVFilter例子 - 纯净版 * Simplest FFmpeg AVfilter Example - Pure * * 雷霄骅 Lei Xiaohua * leixiaohua1020@126.com * 中国传媒大学/数字电视技术 * Communication University of China / Digital TV Technology * http://blog.csdn.net/leixiaohua1020 *  * 本程序使用FFmpeg的AVfilter实现了YUV像素数据的滤镜处理功能。 * 可以给YUV数据添加各种特效功能。 * 是最简单的FFmpeg的AVFilter方面的教程。 * 适合FFmpeg的初学者。 * * This software uses FFmpeg's AVFilter to process YUV raw data. * It can add many excellent effect to YUV data. * It's the simplest example based on FFmpeg's AVFilter.  * Suitable for beginner of FFmpeg  * */#include  #define __STDC_CONSTANT_MACROS #ifdef _WIN32#define snprintf _snprintf//Windowsextern "C"{#include "libavfilter/avfiltergraph.h"#include "libavfilter/buffersink.h"#include "libavfilter/buffersrc.h"#include "libavutil/avutil.h"#include "libavutil/imgutils.h"};#else//Linux...#ifdef __cplusplusextern "C"{#endif#include #include #include #include #include #ifdef __cplusplus};#endif#endif    int main(int argc, char* argv[]){    int ret;    AVFrame *frame_in;AVFrame *frame_out;unsigned char *frame_buffer_in;unsigned char *frame_buffer_out; AVFilterContext *buffersink_ctx;AVFilterContext *buffersrc_ctx;AVFilterGraph *filter_graph;static int video_stream_index = -1; //Input YUVFILE *fp_in=fopen("sintel_480x272_yuv420p.yuv","rb+");if(fp_in==NULL){printf("Error open input file.");return -1;}int in_width=480;int in_height=272; //Output YUVFILE *fp_out=fopen("output.yuv","wb+");if(fp_out==NULL){printf("Error open output file.");return -1;} //const char *filter_descr = "lutyuv='u=128:v=128'";const char *filter_descr = "boxblur";//const char *filter_descr = "hflip";//const char *filter_descr = "hue='h=60:s=-3'";//const char *filter_descr = "crop=2/3*in_w:2/3*in_h";//const char *filter_descr = "drawbox=x=100:y=100:w=100:h=100:color=pink@0.5";//const char *filter_descr = "drawtext=fontfile=arial.ttf:fontcolor=green:fontsize=30:text='Lei Xiaohua'";avfilter_register_all(); char args[512];AVFilter *buffersrc  = avfilter_get_by_name("buffer");AVFilter *buffersink = avfilter_get_by_name("ffbuffersink");AVFilterInOut *outputs = avfilter_inout_alloc();AVFilterInOut *inputs  = avfilter_inout_alloc();enum PixelFormat pix_fmts[] = { AV_PIX_FMT_YUV420P, PIX_FMT_NONE };AVBufferSinkParams *buffersink_params; filter_graph = avfilter_graph_alloc(); /* 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",in_width,in_height,AV_PIX_FMT_YUV420P,1, 25,1,1); ret = avfilter_graph_create_filter(&buffersrc_ctx, buffersrc, "in",args, NULL, filter_graph);if (ret < 0) {printf("Cannot create buffer source");return ret;} /* buffer video sink: to terminate the filter chain. */buffersink_params = av_buffersink_params_alloc();buffersink_params->pixel_fmts = pix_fmts;ret = avfilter_graph_create_filter(&buffersink_ctx, buffersink, "out",NULL, buffersink_params, filter_graph);av_free(buffersink_params);if (ret < 0) {printf("Cannot create buffer sink");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; if ((ret = avfilter_graph_parse_ptr(filter_graph, filter_descr,&inputs, &outputs, NULL)) < 0)return ret; if ((ret = avfilter_graph_config(filter_graph, NULL)) < 0)return ret; frame_in=av_frame_alloc();frame_buffer_in=(unsigned char *)av_malloc(av_image_get_buffer_size(AV_PIX_FMT_YUV420P, in_width,in_height,1));av_image_fill_arrays(frame_in->data, frame_in->linesize,frame_buffer_in,AV_PIX_FMT_YUV420P,in_width, in_height,1); frame_out=av_frame_alloc();frame_buffer_out=(unsigned char *)av_malloc(av_image_get_buffer_size(AV_PIX_FMT_YUV420P, in_width,in_height,1));av_image_fill_arrays(frame_out->data, frame_out->linesize,frame_buffer_out,AV_PIX_FMT_YUV420P,in_width, in_height,1); frame_in->width=in_width;frame_in->height=in_height;frame_in->format=AV_PIX_FMT_YUV420P;    while (1) { if(fread(frame_buffer_in, 1, in_width*in_height*3/2, fp_in)!= in_width*in_height*3/2){break;}//input Y,U,Vframe_in->data[0]=frame_buffer_in;frame_in->data[1]=frame_buffer_in+in_width*in_height;frame_in->data[2]=frame_buffer_in+in_width*in_height*5/4;         if (av_buffersrc_add_frame(buffersrc_ctx, frame_in) < 0) {            printf( "Error while add frame.");            break;        }         /* pull filtered pictures from the filtergraph */ret = av_buffersink_get_frame(buffersink_ctx, frame_out);        if (ret < 0)            break; //output Y,U,Vif(frame_out->format==AV_PIX_FMT_YUV420P){for(int i=0;iheight;i++){fwrite(frame_out->data[0]+frame_out->linesize[0]*i,1,frame_out->width,fp_out);}for(int i=0;iheight/2;i++){fwrite(frame_out->data[1]+frame_out->linesize[1]*i,1,frame_out->width/2,fp_out);}for(int i=0;iheight/2;i++){fwrite(frame_out->data[2]+frame_out->linesize[2]*i,1,frame_out->width/2,fp_out);}}printf("Process 1 frame!");av_frame_unref(frame_out);    } fclose(fp_in);fclose(fp_out); av_frame_free(&frame_in);av_frame_free(&frame_out);    avfilter_graph_free(&filter_graph);     return 0;}

结果

本程序输入为一个名称为“sintel_480x272_yuv420p.yuv”的YUV420P视频数据，输出为一个名称为“output.yuv” 的YUV420P视频数据。输入的视频数据的内容如下所示。

程序中提供了几种特效：

lutyuv='u=128:v=128'

boxblur

hflip

hue='h=60:s=-3'

crop=2/3*in_w:2/3*in_h

drawbox=x=100:y=100:w=100:h=100:color=pink@0.5

drawtext=fontfile=arial.ttf:fontcolor=green:fontsize=30:text='Lei Xiaohua'

可以通过修改程序中的filter_descr字符串实现上述几种特效。下面展示几种特效的效果图。

lutyuv='u=128:v=128'

boxblur

hflip

hue='h=60:s=-3'

crop=2/3*in_w:2/3*in_h

drawbox=x=100:y=100:w=100:h=100:color=pink@0.5

drawtext=fontfile=arial.ttf:fontcolor=green:fontsize=30:text='Lei Xiaohua'

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版权声明：本文为CSDN博主「雷霄骅」的原创文章，遵循CC 4.0 BY-SA版权协议，转载请附上原文出处链接及本声明。

原文链接：https://blog.csdn.net/leixiaohua1020/article/details/50618190

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