FFmpeg 向视频中添加文字

原文地址：http://www.cnblogs.com/wanggang123/p/6707985.html

FFmpeg支持添加文字功能，具体如何将文字叠加到视频中的每一张图片，FFmpeg调用了文字库FreeSerif.ttf。当我们

用到ffmpeg 添加文字功能时 我们需要先下载改文字库，下载地址是http://www.fonts2u.com/free-serif.font，这算是

前期准备工作。准备工作完成以后，我来介绍下Ffmpeg实现视频文件添加文字功能的基本流程，流程图如下图所示：

　　　　　　图1. Ffmpeg 向视频添加文字流程

Ffmpeg 以Filter的方式添加文字，下面给出具体的代码。

1. 打开视频文件。

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int OpenInput(char *fileName) {     context = avformat_alloc_context();     context->interrupt_callback.callback = interrupt_cb;     AVDictionary *format_opts =  nullptr;       int ret = avformat_open_input(&context, fileName, nullptr, &format_opts);     if(ret < 0)     {         return  ret;     }     ret = avformat_find_stream_info(context,nullptr);     av_dump_format(context, 0, fileName, 0);     if(ret >= 0)     {         std::cout <<"open input stream successfully" << endl;     }     return ret; }

2. 初始化 初始化包括输出上下文以及Filter，解码器，编码器四个部分。

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//初始化输出上下文 int OpenOutput(char *fileName) {     int ret = 0;     ret  = avformat_alloc_output_context2(&outputContext, nullptr, "mpegts", fileName);     if(ret < 0)     {         goto Error;     }     ret = avio_open2(&outputContext->pb, fileName, AVIO_FLAG_READ_WRITE,nullptr, nullptr);       if(ret < 0)     {         goto Error;     }       for(int i = 0; i < context->nb_streams; i++)     {         AVStream * stream = avformat_new_stream(outputContext, outPutEncContext->codec);         stream->codec = outPutEncContext;         if(ret < 0)         {             goto Error;         }     }     av_dump_format(outputContext, 0, fileName, 1);     ret = avformat_write_header(outputContext, nullptr);     if(ret < 0)     {         goto Error;     }     if(ret >= 0)         cout <<"open output stream successfully" << endl;     return ret ; Error:     if(outputContext)     {         avformat_close_input(&outputContext);     }     return ret ; }

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//初始化filter<br>int InitFilter(AVCodecContext * codecContext) {     char args[512];     int ret = 0;          AVFilter *buffersrc  = avfilter_get_by_name("buffer");     AVFilter *buffersink = avfilter_get_by_name("buffersink");     AVFilterInOut *outputs = avfilter_inout_alloc();     AVFilterInOut *inputs  = avfilter_inout_alloc();     string  filters_descr ="drawtext=fontfile=D\\\\:FreeSerif.ttf:fontsize=100:text=hello world:x=100:y=100";     enum AVPixelFormat pix_fmts[] = { AV_PIX_FMT_YUV420P, AV_PIX_FMT_YUV420P};       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. */     sprintf_s(args, sizeof(args),         "video_size=%dx%d:pix_fmt=%d:time_base=%d/%d:pixel_aspect=%d/%d",         codecContext->width, codecContext->height, codecContext->pix_fmt,         codecContext->time_base.num, codecContext->time_base.den,         codecContext->sample_aspect_ratio.num, codecContext->sample_aspect_ratio.den);       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;     }       /* buffer video sink: to terminate the filter chain. */     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_YUV420P, AV_OPT_SEARCH_CHILDREN);     if (ret < 0) {         av_log(NULL, AV_LOG_ERROR, "Cannot set output pixel format\n");         goto end;     }       /* 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, filters_descr.c_str(),         &inputs, &outputs, NULL)) < 0)         goto end;       if ((ret = avfilter_graph_config(filter_graph, NULL)) < 0)         goto end;     return ret; end:     avfilter_inout_free(&inputs);     avfilter_inout_free(&outputs);     return ret; }

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//初始化编码器<br>int InitEncoderCodec( int iWidth, int iHeight) {     AVCodec *  pH264Codec = avcodec_find_encoder(AV_CODEC_ID_H264);     if(NULL == pH264Codec)     {         printf("%s", "avcodec_find_encoder failed");         return  -1;     }     outPutEncContext = avcodec_alloc_context3(pH264Codec);     outPutEncContext->gop_size = 30;     outPutEncContext->has_b_frames = 0;     outPutEncContext->max_b_frames = 0;     outPutEncContext->codec_id = pH264Codec->id;     outPutEncContext->time_base.num =context->streams[0]->codec->time_base.num;     outPutEncContext->time_base.den = context->streams[0]->codec->time_base.den;     outPutEncContext->pix_fmt            = *pH264Codec->pix_fmts;     outPutEncContext->width              =  iWidth;     outPutEncContext->height             = iHeight;       outPutEncContext->me_subpel_quality = 0;     outPutEncContext->refs = 1;     outPutEncContext->scenechange_threshold = 0;     outPutEncContext->trellis = 0;     AVDictionary *options = nullptr;     outPutEncContext->flags |= AV_CODEC_FLAG_GLOBAL_HEADER;       int ret = avcodec_open2(outPutEncContext, pH264Codec, &options);     if (ret < 0)     {         printf("%s", "open codec failed");         return  ret;     }     return 1; } <br>//初始化解码器 int InitDecodeCodec(AVCodecID codecId) {     auto codec = avcodec_find_decoder(codecId);     if(!codec)     {         return -1;     }     decoderContext = context->streams[0]->codec;     if (!decoderContext) {         fprintf(stderr, "Could not allocate video codec context\n");         exit(1);     }       if (codec->capabilities & AV_CODEC_CAP_TRUNCATED)         decoderContext->flags |= AV_CODEC_FLAG_TRUNCATED;     int ret = avcodec_open2(decoderContext, codec, NULL);     return ret;   }

源码地址：http://pan.baidu.com/s/1o8Lkozw

视频地址：http://pan.baidu.com/s/1jH4dYN8