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
"); 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
"); 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
"); 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
"); 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