FFmpegFilter简单使用

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Filter，可以认为是一些预定义的范式，可以实现类似积木的多种功能的自由组合。每个filter都有固定数目的输入和输出，而且实际使用中不允许有空 悬的输入输出端。使用文本描述时我们可以通过标识符指定输入和输出端口，将不同filter串联起来，构成更复杂的filter。这就形成了嵌套的 filter。当然每个filter可以通过ffmpeg/ffplay命令行实现，但通常filter更方便。

Filter能做什么？

比较常见的有：

音视频的倍速播放

视频添加删除Logo

视频画中画

放大缩小

画面裁剪

源码

#include 
  
    #include 
   
     #include 
    
      #include 
     
       #include 
      
        #include 
       
         #include 
        
          #include 
         
           static AVFormatContext *fmt_ctx; static AVCodecContext *dec_ctx; AVFilterContext *buffersink_ctx; AVFilterContext *buffersrc_ctx; AVFilterGraph *filter_graph; static int video_stream_index = -1; //打开输入文件 static int open_input_file(const char *filename) { int ret; AVCodec *dec; if ((ret = avformat_open_input(&fmt_ctx, filename, NULL, NULL)) <0) { av_log(NULL, AV_LOG_ERROR, "Cannot open input file\n"); return ret; } if ((ret = avformat_find_stream_info(fmt_ctx, NULL)) <0) { av_log(NULL, AV_LOG_ERROR, "Cannot find stream information\n"); return ret; } //选择视频流 ret = av_find_best_stream(fmt_ctx, AVMEDIA_TYPE_VIDEO, -1, -1, &dec, 0); if (ret <0) { av_log(NULL, AV_LOG_ERROR, "Cannot find a video stream in the input file\n"); return ret; } video_stream_index = ret; /* create decoding context */ dec_ctx = avcodec_alloc_context3(dec); if (!dec_ctx) return AVERROR(ENOMEM); avcodec_parameters_to_context(dec_ctx, fmt_ctx->streams[video_stream_index]->codecpar); //初始化解码器 if ((ret = avcodec_open2(dec_ctx, dec, NULL)) <0) { av_log(NULL, AV_LOG_ERROR, "Cannot open video decoder\n"); return ret; } return 0; } //初始化filter static int init_filters(const char *filters_descr) { char args[512]; int ret = 0; //滤镜输入缓冲区，解码器解码后的数据都会放到buffer中，是一个特殊的filter const AVFilter *buffersrc = avfilter_get_by_name("buffer"); //滤镜输出缓冲区，滤镜处理完后输出的数据都会放在buffersink中，是一个特殊的filter const AVFilter *buffersink = avfilter_get_by_name("buffersink"); AVFilterInOut *outputs = avfilter_inout_alloc(); AVFilterInOut *inputs = avfilter_inout_alloc(); AVRational time_base = fmt_ctx->streams[video_stream_index]->time_base; enum AVPixelFormat pix_fmts[] = {AV_PIX_FMT_YUV420P, AV_PIX_FMT_GRAY8, AV_PIX_FMT_NONE}; //创建filter图，会包含本次使用到的所有过滤器 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. */ snprintf(args, sizeof(args), "video_size=%dx%d:pix_fmt=%d:time_base=%d/%d:pixel_aspect=%d/%d", dec_ctx->width, dec_ctx->height, dec_ctx->pix_fmt, time_base.num, time_base.den, dec_ctx->sample_aspect_ratio.num, dec_ctx->sample_aspect_ratio.den); //创建过滤器实例并将其添加到现有graph中 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; } /* 缓冲视频接收器: 终止过滤器链 */ 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; } /* * Set the endpoints for the filter graph. The filter_graph will * be linked to the graph described by filters_descr. */ /* * The buffer source output must be connected to the input pad of * the first filter described by filters_descr; since the first * filter input label is not specified, it is set to "in" by * default. */ outputs->name = av_strdup("in"); outputs->filter_ctx = buffersrc_ctx; outputs->pad_idx = 0; outputs->next = NULL; /* * The buffer sink input must be connected to the output pad of * the last filter described by filters_descr; since the last * filter output label is not specified, it is set to "out" by * default. */ inputs->name = av_strdup("out"); inputs->filter_ctx = buffersink_ctx; inputs->pad_idx = 0; inputs->next = NULL; //将由字符串描述的图形添加到图形中 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; } //保存YUV数据 static int save_frame(AVFrame *filt_frame, FILE *out){ av_log(NULL, AV_LOG_DEBUG, "do_frame %d\n",filt_frame->format); if(filt_frame->format==AV_PIX_FMT_YUV420P){ av_log(NULL, AV_LOG_ERROR, "save 1 frame\n"); for(int i=0;i
          
           height;i++){ fwrite(filt_frame->data[0]+filt_frame->linesize[0]*i,1,filt_frame->width,out); } for(int i=0;i
           
            height/2;i++){ fwrite(filt_frame->data[1]+filt_frame->linesize[1]*i,1,filt_frame->width/2,out); } for(int i=0;i
            
             height/2;i++){ fwrite(filt_frame->data[2]+filt_frame->linesize[2]*i,1,filt_frame->width/2,out); } } fflush(out); return 0; } int main(int argc, char **argv) { int ret; AVPacket packet; AVFrame *frame; AVFrame *filt_frame; FILE *out = NULL; const char *filter_desc="movie=my_logo.png[wm];[in][wm]overlay=5:5[out]"; //左上角绘制一个logo图片 //"drawbox=30:10:64:64:red";//x= 30,y=10,/Users/liuwei/Desktop/test.mp4"; const char* outfile = "/Users/liuwei/Desktop/new_test.yuv"; av_log_set_level(AV_LOG_DEBUG); frame = av_frame_alloc(); filt_frame = av_frame_alloc(); if (!frame || !filt_frame) { perror("Could not allocate frame"); exit(1); } out = fopen(outfile, "wb"); if(!out){ av_log(NULL, AV_LOG_ERROR, "Failed to open yuv file!\n"); exit(-1); } if ((ret = open_input_file(filename)) <0) goto end; if ((ret = init_filters(filter_desc)) <0) goto end; /* read all packets */ while (1) { // 1 if ((ret = av_read_frame(fmt_ctx, &packet)) <0) break; if (packet.stream_index == video_stream_index) { //2 ret = avcodec_send_packet(dec_ctx, &packet); if (ret <0) { av_log(NULL, AV_LOG_ERROR, "Error while sending a packet to the decoder\n"); break; } while (ret >= 0) { //3 ret = avcodec_receive_frame(dec_ctx, frame); if (ret == AVERROR(EAGAIN) || ret == AVERROR_EOF) { break; } else if (ret <0) { av_log(NULL, AV_LOG_ERROR, "Error while receiving a frame from the decoder\n"); goto end; } frame->pts = frame->best_effort_timestamp; /*4 push the decoded frame into the filtergraph */ if (av_buffersrc_add_frame_flags(buffersrc_ctx, frame, AV_BUFFERSRC_FLAG_KEEP_REF) <0) { av_log(NULL, AV_LOG_ERROR, "Error while feeding the filtergraph\n"); break; } /* pull filtered frames from the filtergraph */ while (1) { //5 ret = av_buffersink_get_frame(buffersink_ctx, filt_frame); if (ret == AVERROR(EAGAIN) || ret == AVERROR_EOF) break; if (ret <0) goto end; save_frame(filt_frame,out); av_frame_unref(filt_frame); } av_frame_unref(frame); } } av_packet_unref(&packet); } end: avfilter_graph_free(&filter_graph); avcodec_free_context(&dec_ctx); avformat_close_input(&fmt_ctx); av_frame_free(&frame); av_frame_free(&filt_frame); if (ret <0 && ret != AVERROR_EOF) { fprintf(stderr, "Error occurred: %s\n", av_err2str(ret)); exit(1); } exit(0); } 
            
           
          
         
        
       
      
     
    
   
  

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代码会将一个MP4文件在左上角添加一个图片后输出为yuv文件，这个图片如果背景是透明的就是水印啦（主要是懒得做透明背景图片）。

"drawbox=30:10:64:64:red";x= 30,y=10,width=64,height=64,color=red, 绘制一个红色正方形

`"scale=iw*2:ih*2"`视频缩放，iw 表示输入视频的宽，ih表示输入视频的高。*2 表示放大两倍,如果是/2表示缩小两倍

`"crop=320:240:0:0"`视频裁剪，crop=width:height : x : y，其中 width 和 height 表示裁剪后的尺寸，x:y 表示裁剪区域的左上角坐标

还有很多filter可以使用，并且可以实现自定义filter。

原文链接

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