FFmpeg C++实现视频水印

要在视频中添加水印，可以使用 FFmpeg 库中提供的过滤器来实现。以下是一个基本的 C 代码示例，它使用 FFmpeg 库中的过滤器来将文本水印添加到视频中：

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <unistd.h>

#include <libavformat/avformat.h>
#include <libavfilter/avfiltergraph.h>
#include <libavfilter/buffersrc.h>
#include <libavfilter/buffersink.h>

int main(int argc, char **argv) {

    AVFilterContext *buffersrc_ctx;
    AVFilterContext *buffersink_ctx;
    AVFilterGraph *filter_graph;
    int ret;

    if (argc != 3) {
        fprintf(stderr, "Usage: %s <input file> <output file>\n", argv[0]);
        exit(1);
    }

    av_register_all();
    avfilter_register_all();

    AVFormatContext *fmt_ctx = NULL;
    ret = avformat_open_input(&fmt_ctx, argv[1], NULL, NULL);
    if (ret < 0) {
        fprintf(stderr, "Could not open input file '%s'", argv[1]);
        exit(1);
    }

    ret = avformat_find_stream_info(fmt_ctx, NULL);
    if (ret < 0) {
        fprintf(stderr, "Could not find stream information");
        exit(1);
    }

    av_dump_format(fmt_ctx, 0, argv[1], 0);

    AVCodecContext *codec_ctx = NULL;
    int video_stream_index = av_find_best_stream(fmt_ctx, AVMEDIA_TYPE_VIDEO, -1, -1, NULL, 0);
    if (video_stream_index < 0) {
        fprintf(stderr, "Could not find video stream in input file");
        exit(1);
    }

    AVStream *video_stream = fmt_ctx->streams[video_stream_index];
    codec_ctx = video_stream->codec;

    AVCodec *decoder = avcodec_find_decoder(codec_ctx->codec_id);
    if (!decoder) {
        fprintf(stderr, "Failed to find decoder for stream #%u codec ID %d\n", video_stream_index, codec_ctx->codec_id);
        exit(1);
    }

    ret = avcodec_open2(codec_ctx, decoder, NULL);
    if (ret < 0) {
        fprintf(stderr, "Failed to open decoder for stream #%u\n", video_stream_index);
        exit(1);
    }

    AVFrame *frame = av_frame_alloc();
    AVPacket packet;

    av_init_packet(&packet);

    filter_graph = avfilter_graph_alloc();
    char args[512];
    snprintf(args, sizeof(args),
             "drawtext=text='My Watermark':x=(w-text_w)/2:y=(h-text_h)/2:fontfile=/usr/share/fonts/truetype/freefont/FreeSerif.ttf:fontsize=48:fontcolor=white");
    const AVFilter *buffersrc = avfilter_get_by_name("buffer");
    const AVFilter *buffersink = avfilter_get_by_name("buffersink");
    AVFilterInOut *outputs = avfilter_inout_alloc();
    AVFilterInOut *inputs = avfilter_inout_alloc();
    enum AVPixelFormat pix_fmts[] = {AV_PIX_FMT_YUV420P, AV_PIX_FMT_NONE};

    sprintf(args, "video_size=%dx%d:pix_fmt=%d:time_base=%d/%d:pixel_aspect=%d/%d",
            codec_ctx->width, codec_ctx->height, codec_ctx->pix_fmt,
            video_stream->