FFMPEG中有一个类库：libavfilter。该类库提供了各种视音频过滤器。之前一直没有怎么使用过这个类库，最近看了一下它的使用说明，发现还是很强大的，有很多现成的filter供使用，完成视频的处理很方便。在此将它的一个例子基础上完成了一个水印叠加器，并且移植到了VC2010下，方便开发人员学习研究它的使用方法。

该例子完成了一个水印叠加的功能。可以将一张透明背景的PNG图片作为水印叠加到一个视频文件上。

下面直接贴上代码：

/* * 最简单的基于FFmpeg的AVFilter例子（叠加水印）* Simplest FFmpeg AVfilter Example (Watermark)** 雷霄骅 Lei Xiaohua* leixiaohua1020@126.com* 中国传媒大学/数字电视技术* Communication University of China / Digital TV Technology* http://blog.csdn.net/leixiaohua1020* * 本程序使用FFmpeg的AVfilter实现了视频的水印叠加功能。* 可以将一张PNG图片作为水印叠加到视频上。* 是最简单的FFmpeg的AVFilter方面的教程。* 适合FFmpeg的初学者。** This software uses FFmpeg's AVFilter to add watermark in a video file.* It can add a PNG format picture as watermark to a video file.* It's the simplest example based on FFmpeg's AVFilter. * Suitable for beginner of FFmpeg **/
#include "stdafx.h"#define ENABLE_SDL 1
#define ENABLE_YUVFILE 1extern "C"
{
#include "libavcodec/avcodec.h"
#include "libavformat/avformat.h"
#include "libavfilter/avfiltergraph.h"
#include "libavfilter/avcodec.h"
#include "libavfilter/buffersink.h"
#include "libavfilter/buffersrc.h"
#include "libavutil/avutil.h"
#include "libswscale/swscale.h"//SDL
#include "sdl/SDL.h"
#include "sdl/SDL_thread.h"
};const char *filter_descr = "movie=my_logo.png[wm];[in][wm]overlay=5:5[out]";static AVFormatContext *pFormatCtx;
static AVCodecContext *pCodecCtx;
AVFilterContext *buffersink_ctx;
AVFilterContext *buffersrc_ctx;
AVFilterGraph *filter_graph;
static int video_stream_index = -1;
static int64_t last_pts = AV_NOPTS_VALUE;static int open_input_file(const char *filename)
{int ret;AVCodec *dec;if ((ret = avformat_open_input(&pFormatCtx, filename, NULL, NULL)) < 0) {av_log(NULL, AV_LOG_ERROR, "Cannot open input file\n");return ret;}if ((ret = avformat_find_stream_info(pFormatCtx, NULL)) < 0) {av_log(NULL, AV_LOG_ERROR, "Cannot find stream information\n");return ret;}/* select the video stream */ret = av_find_best_stream(pFormatCtx, AVMEDIA_TYPE_VIDEO, -1, -1, &dec, 0);if (ret < 0) {av_log(NULL, AV_LOG_ERROR, "Cannot find a video stream in the input file\n");return ret;}video_stream_index = ret;pCodecCtx = pFormatCtx->streams[video_stream_index]->codec;/* init the video decoder */if ((ret = avcodec_open2(pCodecCtx, dec, NULL)) < 0) {av_log(NULL, AV_LOG_ERROR, "Cannot open video decoder\n");return ret;}return 0;
}static int init_filters(const char *filters_descr)
{char args[512];int ret;AVFilter *buffersrc  = avfilter_get_by_name("buffer");AVFilter *buffersink = avfilter_get_by_name("ffbuffersink");AVFilterInOut *outputs = avfilter_inout_alloc();AVFilterInOut *inputs  = avfilter_inout_alloc();enum PixelFormat pix_fmts[] = { PIX_FMT_GRAY8, PIX_FMT_NONE };AVBufferSinkParams *buffersink_params;filter_graph = avfilter_graph_alloc();/* buffer video source: the decoded frames from the decoder will be inserted here. */_snprintf(args, sizeof(args),"video_size=%dx%d:pix_fmt=%d:time_base=%d/%d:pixel_aspect=%d/%d",pCodecCtx->width, pCodecCtx->height, pCodecCtx->pix_fmt,pCodecCtx->time_base.num, pCodecCtx->time_base.den,pCodecCtx->sample_aspect_ratio.num, pCodecCtx->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");return ret;}/* buffer video sink: to terminate the filter chain. */buffersink_params = av_buffersink_params_alloc();buffersink_params->pixel_fmts = pix_fmts;ret = avfilter_graph_create_filter(&buffersink_ctx, buffersink, "out",NULL, buffersink_params, filter_graph);av_free(buffersink_params);if (ret < 0) {av_log(NULL, AV_LOG_ERROR, "Cannot create buffer sink\n");return ret;}/* 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(filter_graph, filters_descr,&inputs, &outputs, NULL)) < 0)return ret;if ((ret = avfilter_graph_config(filter_graph, NULL)) < 0)return ret;return 0;
}int _tmain(int argc, _TCHAR* argv[])
{int ret;AVPacket packet;AVFrame frame;int got_frame;if (argc != 2) {fprintf(stderr, "Usage: %s file\n", argv[0]);return -1;}avcodec_register_all();av_register_all();avfilter_register_all();if ((ret = open_input_file(argv[1])) < 0)goto end;if ((ret = init_filters(filter_descr)) < 0)goto end;
#if ENABLE_YUVFILEFILE *fp_yuv=fopen("test.yuv","wb+");
#endif
#if ENABLE_SDLSDL_Surface *screen; SDL_Overlay *bmp; SDL_Rect rect;if(SDL_Init(SDL_INIT_VIDEO | SDL_INIT_AUDIO | SDL_INIT_TIMER)) {  printf( "Could not initialize SDL - %s\n", SDL_GetError()); return -1;} screen = SDL_SetVideoMode(pCodecCtx->width, pCodecCtx->height, 0, 0);if(!screen) {  printf("SDL: could not set video mode - exiting\n");  return -1;}bmp = SDL_CreateYUVOverlay(pCodecCtx->width, pCodecCtx->height,SDL_YV12_OVERLAY, screen);
#endif/* read all packets */while (1) {AVFilterBufferRef *picref;if ((ret = av_read_frame(pFormatCtx, &packet)) < 0)break;if (packet.stream_index == video_stream_index) {avcodec_get_frame_defaults(&frame);got_frame = 0;ret = avcodec_decode_video2(pCodecCtx, &frame, &got_frame, &packet);if (ret < 0) {av_log(NULL, AV_LOG_ERROR, "Error decoding video\n");break;}if (got_frame) {frame.pts = av_frame_get_best_effort_timestamp(&frame);/* push the decoded frame into the filtergraph */if (av_buffersrc_add_frame(buffersrc_ctx, &frame) < 0) {av_log(NULL, AV_LOG_ERROR, "Error while feeding the filtergraph\n");break;}/* pull filtered pictures from the filtergraph */while (1) {ret = av_buffersink_get_buffer_ref(buffersink_ctx, &picref, 0);if (ret == AVERROR(EAGAIN) || ret == AVERROR_EOF)break;if (ret < 0)goto end;if (picref) {
#if ENABLE_YUVFILEint y_size=picref->video->w*picref->video->h;fwrite(picref->data[0],1,y_size,fp_yuv);fwrite(picref->data[1],1,y_size/4,fp_yuv);fwrite(picref->data[2],1,y_size/4,fp_yuv);
#endif#if ENABLE_SDLSDL_LockYUVOverlay(bmp);bmp->pixels[0]=picref->data[0];bmp->pixels[2]=picref->data[1];bmp->pixels[1]=picref->data[2];     bmp->pitches[0]=picref->linesize[0];bmp->pitches[2]=picref->linesize[1];   bmp->pitches[1]=picref->linesize[2];SDL_UnlockYUVOverlay(bmp); rect.x = 0;    rect.y = 0;    rect.w = picref->video->w;    rect.h = picref->video->h;    SDL_DisplayYUVOverlay(bmp, &rect); //Delay 40msSDL_Delay(40);
#endifavfilter_unref_bufferp(&picref);}}}}av_free_packet(&packet);}
#if ENABLE_YUVFILEfclose(fp_yuv);
#endif
end:avfilter_graph_free(&filter_graph);if (pCodecCtx)avcodec_close(pCodecCtx);avformat_close_input(&pFormatCtx);if (ret < 0 && ret != AVERROR_EOF) {char buf[1024];av_strerror(ret, buf, sizeof(buf));fprintf(stderr, "Error occurred: %s\n", buf);return -1;}return 0;
}

程序的运行效果如图所示。

需要叠加的水印为一张PNG（透明）图片（在这里是my_logo.png）。

需要叠加的视频为一个普通的FLV格式的视频（在这里是cuc_ieschool.flv）。

程序运行的时候，会通过SDL显示水印叠加的结果，如图所示。此外，也可以将水印叠加后的解码数据输出成文件。

注：SDL显示和输出YUV可以通过程序最前面的宏控制：

#define ENABLE_SDL 1
#define ENABLE_YUVFILE 1

输出的YUV文件如图所示。

SourceForge项目主页：

https://sourceforge.net/projects/simplestffmpegvideofilter/

CSDN项目下载地址：

http://download.csdn.net/detail/leixiaohua1020/7465861

注：由于失误，CSDN上的项目少了一个SDL.dll文件，去SDL官网
http://www.libsdl.org/download-1.2.php
下载一个Runtime Libraries即可

SourceForge上项目已经修正该问题。