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