extern "C" void debugout(const char *fmt,...); 这一句代码什么意思

这段代码是用于声明一个 C 语言的外部函数 debugout。其中 extern "C" 是用来指定函数按照 C 语言的方式进行编译和链接，而不是 C++ 的方式。void 是函数的返回类型，debugout 是函数的名称，const char *fmt 是函数的第一个参数，表示一个指向常量字符的指针，... 表示函数可以接受可变数量的参数。整体上，这段代码的意思是声明了一个函数 debugout，该函数接受一个格式化字符串参数 fmt 和可变数量的参数，并且没有返回值。

相关问题

Ffmpeg 如何为视频加水印，c++纯代码实现，只需要Filter部分代码

### 回答1：
为视频加水印可以使用FFmpeg中的`overlay`过滤器。以下是使用纯C代码实现的示例：

AVFilterContext *buffersrc_ctx;
AVFilterContext *buffersink_ctx;
AVFilterGraph *filter_graph;
AVFilter *buffersrc = avfilter_get_by_name("buffer");
AVFilter *buffersink = avfilter_get_by_name("buffersink");
AVFilterInOut *outputs = avfilter_inout_alloc();
AVFilterInOut *inputs = avfilter_inout_alloc();
const char *filter_descr = "overlay=10:10";
int ret;

filter_graph = avfilter_graph_alloc();
if (!outputs || !inputs || !filter_graph) {
    ret = AVERROR(ENOMEM);
    goto end;
}

// 添加 buffer 过滤器到过滤器图中
ret = avfilter_graph_create_filter(&buffersrc_ctx, buffersrc, "in",
                                    "video_size=1920x1080:pix_fmt=0:time_base=1/25",
                                    NULL, filter_graph);
if (ret < 0) {
    av_log(NULL, AV_LOG_ERROR, "Cannot create buffer source\n");
    goto end;
}

// 添加 buffersink 过滤器到过滤器图中
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;
}

// 设置 filter_graph 的输入输出链
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;

// 添加 filter 到 filter_graph 中
ret = avfilter_graph_parse_ptr(filter_graph, filter_descr, &inputs, &outputs, NULL);
if (ret < 0) {
    goto end;
}

// 链接 filter
ret = avfilter_graph_config(filter_graph, NULL);
if (ret < 0) {
    goto end;
}

end:
avfilter_inout_free(&inputs);
avfilter_inout_free(&outputs);
avfilter_graph_free(&filter_graph);

以上代码将在视频的左上角添加一个10像素的水印。可以通过修改`filter_descr`来调整水印的位置和大小。

### 回答2：
在使用 Ffmpeg 为视频加水印时，可以通过 Filter 部分的代码来实现。

首先，需要引入 Ffmpeg 头文件和相关的库文件：

extern "C" {
#include <libavfilter/avfilter.h>
#include <libavfilter/buffersink.h>
#include <libavfilter/buffersrc.h>
}

#pragma comment(lib, "libavfilter.lib")
#pragma comment(lib, "libavdevice.lib")
#pragma comment(lib, "libavformat.lib")
#pragma comment(lib, "libavcodec.lib")
#pragma comment(lib, "libswscale.lib")

然后，可以定义一个函数来实现添加水印的功能，如下所示：

void addWatermark(const char* inputFileName, const char* watermarkFileName, const char* outputFileName) {
    AVFilterContext* buffersink_ctx;
    AVFilterContext* buffersrc_ctx;
    AVFilterGraph* filter_graph;
    AVFormatContext* format_ctx;
    AVPacket packet;
    int ret;

    // 打开输入文件
    ret = avformat_open_input(&format_ctx, inputFileName, 0, 0);
    if (ret < 0) {
        // 处理打开输入文件失败的情况
        return;
    }

    // 查找流信息
    ret = avformat_find_stream_info(format_ctx, 0);
    if (ret < 0) {
        // 处理查找流信息失败的情况
        avformat_close_input(&format_ctx);
        return;
    }

    // 创建图像过滤器核心
    filter_graph = avfilter_graph_alloc();
    if (!filter_graph) {
        // 处理创建图像过滤器核心失败的情况
        avformat_close_input(&format_ctx);
        return;
    }

    // 打开输入过滤器源（Source）
    const AVFilter* buffersrc = avfilter_get_by_name("buffer");
    buffersrc_ctx = avfilter_graph_alloc_filter(filter_graph, buffersrc, "src");
    if (!buffersrc_ctx) {
        // 处理打开输入过滤器源失败的情况
        avfilter_graph_free(&filter_graph);
        avformat_close_input(&format_ctx);
        return;
    }

    // 设置输入过滤器源的参数
    av_opt_set_int_list(buffersrc_ctx, "pix_fmts", fmts, -1, AV_OPT_SEARCH_CHILDREN);
    av_opt_set_int(buffersrc_ctx, "width", format_ctx->streams[0]->codecpar->width, AV_OPT_SEARCH_CHILDREN);
    av_opt_set_int(buffersrc_ctx, "height", format_ctx->streams[0]->codecpar->height, AV_OPT_SEARCH_CHILDREN);

    // 打开输出过滤器接收器（Sink）
    const AVFilter* buffersink = avfilter_get_by_name("buffersink");
    buffersink_ctx = avfilter_graph_alloc_filter(filter_graph, buffersink, "sink");
    if (!buffersink_ctx) {
        // 处理打开输出过滤器接收器失败的情况
        avfilter_graph_free(&filter_graph);
        avformat_close_input(&format_ctx);
        return;
    }

    // 初始化图像过滤器核心
    ret = avfilter_graph_parse_ptr(filter_graph, filter_desc, &buffersrc_ctx, &buffersink_ctx, NULL);
    if (ret < 0) {
        // 处理初始化图像过滤器核心失败的情况
        avfilter_graph_free(&filter_graph);
        avformat_close_input(&format_ctx);
        return;
    }

    // 链接图像过滤器核心
    ret = avfilter_graph_config(filter_graph, NULL);
    if (ret < 0) {
        // 处理链接图像过滤器核心失败的情况
        avfilter_graph_free(&filter_graph);
        avformat_close_input(&format_ctx);
        return;
    }

    // 读取水印文件
    AVFormatContext* watermark_format_ctx;
    ret = avformat_open_input(&watermark_format_ctx, watermarkFileName, 0, 0);
    if (ret < 0) {
        // 处理读取水印文件失败的情况
        avfilter_graph_free(&filter_graph);
        avformat_close_input(&format_ctx);
        return;
    }

    // 从水印文件中读取数据包
    while (av_read_frame(watermark_format_ctx, &packet) >= 0) {
        // 对水印的数据包进行过滤
        if (packet.stream_index == 0) {
            av_buffersrc_add_frame_flags(buffersrc_ctx, packet.data, AV_BUFFERSRC_FLAG_PUSH);
        }
        av_packet_unref(&packet);
    }

    // 处理输出过滤器接收器（Sink）的输出帧
    while (1) {
        AVFrame* frame = av_frame_alloc();
        ret = av_buffersink_get_frame(buffersink_ctx, frame);
        if (ret < 0) {
            // 处理处理输出过滤器接收器的输出帧失败的情况
            av_frame_unref(frame);
            break;
        }

        // 对输出帧进行处理，例如进行水印贴图
        // ...

        av_frame_unref(frame);
    }

    // 释放资源
    avfilter_graph_free(&filter_graph);
    avformat_close_input(&format_ctx);
    avformat_close_input(&watermark_format_ctx);
}

以上是一个参考的基本代码示例，其中需要替换部分代码来符合实际需求。此外，添加水印的具体处理方法，例如进行水印贴图，需要根据实际情况实现。

c/c++使用ffmpeg库推流本地文件，并使用av_seek_frame实现跳转功能的完整代码

这里是使用ffmpeg库推流本地文件，并使用av_seek_frame实现跳转功能的完整C++代码：

#include <iostream>
#include <string>

extern "C" {
#include <libavformat/avformat.h>
#include <libavutil/mathematics.h>
}

#define STREAM_DURATION 10.0
#define STREAM_FRAME_RATE 25 /* 25 images/s */
#define STREAM_PIX_FMT AV_PIX_FMT_YUV420P /* default pix_fmt */

/* add a video output stream */
static AVStream *add_video_stream(AVFormatContext *oc, enum AVCodecID codec_id) {
    AVCodecContext *c;
    AVStream *st;

    st = avformat_new_stream(oc, NULL);
    if (!st) {
        std::cerr << "Could not allocate stream" << std::endl;
        exit(1);
    }

    c = st->codec;
    c->codec_id = codec_id;
    c->codec_type = AVMEDIA_TYPE_VIDEO;

    /* put sample parameters */
    c->bit_rate = 400000;
    /* resolution must be a multiple of two */
    c->width = 352;
    c->height = 288;
    /* frames per second */
    c->time_base = (AVRational) { 1, STREAM_FRAME_RATE };
    st->time_base = c->time_base;

    c->gop_size = 12; /* emit one intra frame every twelve frames at most */
    c->pix_fmt = STREAM_PIX_FMT;

    /* some formats want stream headers to be separate */
    if (oc->oformat->flags & AVFMT_GLOBALHEADER)
        c->flags |= AV_CODEC_FLAG_GLOBAL_HEADER;

    return st;
}

/* open the output file, and allocate the format context */
static void open_output_file(const std::string &filename, AVFormatContext **oc, AVOutputFormat *fmt) {
    int ret;

    /* allocate the output media context */
    avformat_alloc_output_context2(oc, fmt, NULL, filename.c_str());
    if (!(*oc)) {
        std::cerr << "Could not create output context" << std::endl;
        exit(1);
    }

    /* add the video stream using the default format codecs and initialize the codecs */
    add_video_stream(*oc, (*oc)->oformat->video_codec);

    /* open the output file, if needed */
    if (!((*oc)->oformat->flags & AVFMT_NOFILE)) {
        ret = avio_open(&(*oc)->pb, filename.c_str(), AVIO_FLAG_WRITE);
        if (ret < 0) {
            std::cerr << "Could not open output file" << std::endl;
            exit(1);
        }
    }

    /* write the stream header, if any */
    ret = avformat_write_header(*oc, NULL);
    if (ret < 0) {
        std::cerr << "Error occurred when opening output file" << std::endl;
        exit(1);
    }
}

/* close the output file and free the format context */
static void close_output_file(AVFormatContext *oc) {
    /* write the trailer, if any */
    av_write_trailer(oc);

    /* close the output file */
    if (!(oc->oformat->flags & AVFMT_NOFILE))
        avio_closep(&oc->pb);

    /* free the stream */
    avformat_free_context(oc);
}

/* seek to a specific frame in a video file */
static void seek_to_frame(AVFormatContext *fmt_ctx, int stream_index, int64_t timestamp) {
    int ret;

    /* seek to the timestamp */
    ret = av_seek_frame(fmt_ctx, stream_index, timestamp, AVSEEK_FLAG_BACKWARD);
    if (ret < 0) {
        std::cerr << "Error seeking to timestamp " << timestamp << std::endl;
        exit(1);
    }

    /* flush the codec buffers */
    avcodec_flush_buffers(fmt_ctx->streams[stream_index]->codec);
}

int main(int argc, char **argv) {
    if (argc != 2) {
        std::cerr << "Usage: " << argv[0] << " <output file>" << std::endl;
        return 1;
    }

    AVOutputFormat *fmt;
    AVFormatContext *oc;
    AVPacket pkt;
    int frame_count, i;
    double t, tincr;
    int64_t next_pts;

    /* register all codecs and formats */
    av_register_all();

    /* allocate the output media context */
    fmt = av_guess_format(NULL, argv[1], NULL);
    if (!fmt) {
        std::cerr << "Could not determine output format" << std::endl;
        return 1;
    }
    open_output_file(argv[1], &oc, fmt);

    /* initialize the frame counter */
    frame_count = 0;

    /* initialize the timestamp increment */
    tincr = 2 * M_PI * STREAM_FRAME_RATE / STREAM_DURATION;
    next_pts = 0;

    /* main loop */
    for (i = 0; i < 100; i++) {
        AVStream *st;
        AVCodecContext *c;
        AVRational time_base;
        AVFrame *frame;
        int got_packet = 0;
        int ret;

        /* get the video stream */
        st = oc->streams[0];
        c = st->codec;
        time_base = st->time_base;

        /* allocate a new frame */
        frame = av_frame_alloc();
        if (!frame) {
            std::cerr << "Could not allocate video frame" << std::endl;
            exit(1);
        }

        /* generate synthetic video */
        frame->pts = av_rescale_q(frame_count, time_base, c->time_base);
        frame->format = c->pix_fmt;
        frame->width = c->width;
        frame->height = c->height;
        ret = av_frame_get_buffer(frame, 0);
        if (ret < 0) {
            std::cerr << "Could not allocate frame data" << std::endl;
            exit(1);
        }
        for (int y = 0; y < c->height; y++)
            for (int x = 0; x < c->width; x++)
                frame->data[0][y * frame->linesize[0] + x] = x + y + frame_count * 3;
        for (int y = 0; y < c->height / 2; y++) {
            for (int x = 0; x < c->width / 2; x++) {
                frame->data[1][y * frame->linesize[1] + x] = 128 + y + frame_count * 2;
                frame->data[2][y * frame->linesize[2] + x] = 64 + x + frame_count * 5;
            }
        }

        /* encode the frame */
        av_init_packet(&pkt);
        pkt.data = NULL;
        pkt.size = 0;
        ret = avcodec_encode_video2(c, &pkt, frame, &got_packet);
        if (ret < 0) {
            std::cerr << "Error encoding video frame" << std::endl;
            exit(1);
        }

        /* if the frame was encoded, write it to the file */
        if (got_packet) {
            pkt.stream_index = st->index;
            av_packet_rescale_ts(&pkt, time_base, st->time_base);
            ret = av_interleaved_write_frame(oc, &pkt);
            if (ret < 0) {
                std::cerr << "Error while writing video frame" << std::endl;
                exit(1);
            }
        }

        /* increase the frame count */
        frame_count++;

        /* calculate the next presentation timestamp */
        t = (double)frame_count / STREAM_FRAME_RATE;
        next_pts += (int64_t)(tincr * 1000);
        if (next_pts > (double)av_gettime()) {
            av_usleep(next_pts - av_gettime());
        }

        /* free the frame */
        av_frame_free(&frame);
    }

    /* seek to a specific frame */
    seek_to_frame(oc, 0, 30);

    /* continue encoding frames */
    for (; i < 200; i++) {
        AVStream *st;
        AVCodecContext *c;
        AVRational time_base;
        AVFrame *frame;
        int got_packet = 0;
        int ret;

        /* get the video stream */
        st = oc->streams[0];
        c = st->codec;
        time_base = st->time_base;

        /* allocate a new frame */
        frame = av_frame_alloc();
        if (!frame) {
            std::cerr << "Could not allocate video frame" << std::endl;
            exit(1);
        }

        /* generate synthetic video */
        frame->pts = av_rescale_q(frame_count, time_base, c->time_base);
        frame->format = c->pix_fmt;
        frame->width = c->width;
        frame->height = c->height;
        ret = av_frame_get_buffer(frame, 0);
        if (ret < 0) {
            std::cerr << "Could not allocate frame data" << std::endl;
            exit(1);
        }
        for (int y = 0; y < c->height; y++)
            for (int x = 0; x < c->width; x++)
                frame->data[0][y * frame->linesize[0] + x] = x + y + frame_count * 3;
        for (int y = 0; y < c->height / 2; y++) {
            for (int x = 0; x < c->width / 2; x++) {
                frame->data[1][y * frame->linesize[1] + x] = 128 + y + frame_count * 2;
                frame->data[2][y * frame->linesize[2] + x] = 64 + x + frame_count * 5;
            }
        }

        /* encode the frame */
        av_init_packet(&pkt);
        pkt.data = NULL;
        pkt.size = 0;
        ret = avcodec_encode_video2(c, &pkt, frame, &got_packet);
        if (ret < 0) {
            std::cerr << "Error encoding video frame" << std::endl;
            exit(1);
        }

        /* if the frame was encoded, write it to the file */
        if (got_packet) {
            pkt.stream_index = st->index;
            av_packet_rescale_ts(&pkt, time_base, st->time_base);
            ret = av_interleaved_write_frame(oc, &pkt);
            if (ret < 0) {
                std::cerr << "Error while writing video frame" << std::endl;
                exit(1);
            }
        }

        /* increase the frame count */
        frame_count++;

        /* calculate the next presentation timestamp */
        t = (double)frame_count / STREAM_FRAME_RATE;
        next_pts += (int64_t)(tincr * 1000);
        if (next_pts > (double)av_gettime()) {
            av_usleep(next_pts - av_gettime());
        }

        /* free the frame */
        av_frame_free(&frame);
    }

    /* close the output file and free the format context */
    close_output_file(oc);

    return 0;
}

这个代码会生成一个10秒的视频，并在第30帧处进行跳转，继续生成另外10秒的视频。视频中的图像是随机生成的。你可以根据自己的需求进行修改。