Ffmpeg 视频教程 向视频中添加文字

    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;
 
}

 

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posted @   王纲  阅读(9893)  评论(0)  编辑  收藏  举报
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