(一) ffmpeg filter学习-使用流程

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。需要注意的是，其叠加工作是在解码后的YUV像素数据的基础上完成的。程序支持使用SDL显示叠加后的YUV数据。也可以将叠加后的YUV输出成文件。

流程图

下面附一张使用FFmpeg的libavfilter的流程图。可以看出使用libavfilter还是需要做不少的初始化工作的。但是使用的时候还是比较简单的，就两个重要的函数：av_buffersrc_add_frame()和av_buffersink_get_buffer_ref()。

PS：这张图中只列出了和libavfilter有关的函数和结构体。代码中其它函数可以参考：100行代码实现最简单的基于FFMPEG+SDL的视频播放器（SDL1.x）

代码

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 <stdio.h>  
  
#define __STDC_CONSTANT_MACROS  
  
#ifdef _WIN32  
#define snprintf _snprintf  
//Windows  
extern "C"  
{  
#include "libavcodec/avcodec.h"  
#include "libavformat/avformat.h"  
#include "libavfilter/avfiltergraph.h"  
#include "libavfilter/buffersink.h"  
#include "libavfilter/buffersrc.h"  
#include "libavutil/avutil.h"  
#include "libswscale/swscale.h"  
#include "SDL/SDL.h"  
};  
#else  
//Linux...  
#ifdef __cplusplus  
extern "C"  
{  
#endif  
#include <libavcodec/avcodec.h>  
#include <libavformat/avformat.h>  
#include <libavfilter/avfiltergraph.h>  
#include <libavfilter/buffersink.h>  
#include <libavfilter/buffersrc.h>  
#include <libavutil/avutil.h>  
#include <libswscale/swscale.h>  
#include <SDL/SDL.h>  
#ifdef __cplusplus  
};  
#endif  
#endif  
  
//Enable SDL?  
#define ENABLE_SDL 1  
//Output YUV data?  
#define ENABLE_YUVFILE 1  
  
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 int open_input_file(const char *filename)  
{  
    int ret;  
    AVCodec *dec;  
  
    if ((ret = avformat_open_input(&pFormatCtx, filename, NULL, NULL)) < 0) {  
        printf( "Cannot open input file
");  
        return ret;  
    }  
  
    if ((ret = avformat_find_stream_info(pFormatCtx, NULL)) < 0) {  
        printf( "Cannot find stream information
");  
        return ret;  
    }  
  
    /* select the video stream */  
    ret = av_find_best_stream(pFormatCtx, AVMEDIA_TYPE_VIDEO, -1, -1, &dec, 0);  
    if (ret < 0) {  
        printf( "Cannot find a video stream in the input file
");  
        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) {  
        printf( "Cannot open video decoder
");  
        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 AVPixelFormat pix_fmts[] = { AV_PIX_FMT_YUV420P, AV_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) {  
        printf("Cannot create buffer source
");  
        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) {  
        printf("Cannot create buffer sink
");  
        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_ptr(filter_graph, filters_descr,  
                                    &inputs, &outputs, NULL)) < 0)  
        return ret;  
  
    if ((ret = avfilter_graph_config(filter_graph, NULL)) < 0)  
        return ret;  
    return 0;  
}  
  
  
int main(int argc, char* argv[])  
{  
    int ret;  
    AVPacket packet;  
    AVFrame *pFrame;  
    AVFrame *pFrame_out;  
  
    int got_frame;  
  
    av_register_all();  
    avfilter_register_all();  
  
    if ((ret = open_input_file("cuc_ieschool.flv")) < 0)  
        goto end;  
    if ((ret = init_filters(filter_descr)) < 0)  
        goto end;  
  
#if ENABLE_YUVFILE  
    FILE *fp_yuv=fopen("test.yuv","wb+");  
#endif  
#if ENABLE_SDL  
    SDL_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
", SDL_GetError());   
        return -1;  
    }   
    screen = SDL_SetVideoMode(pCodecCtx->width, pCodecCtx->height, 0, 0);  
    if(!screen) {    
        printf("SDL: could not set video mode - exiting
");    
        return -1;  
    }  
    bmp = SDL_CreateYUVOverlay(pCodecCtx->width, pCodecCtx->height,SDL_YV12_OVERLAY, screen);   
  
    SDL_WM_SetCaption("Simplest FFmpeg Video Filter",NULL);  
#endif  
  
    pFrame=av_frame_alloc();  
    pFrame_out=av_frame_alloc();  
  
    /* read all packets */  
    while (1) {  
  
        ret = av_read_frame(pFormatCtx, &packet);  
        if (ret< 0)  
            break;  
  
        if (packet.stream_index == video_stream_index) {  
            got_frame = 0;  
            ret = avcodec_decode_video2(pCodecCtx, pFrame, &got_frame, &packet);  
            if (ret < 0) {  
                printf( "Error decoding video
");  
                break;  
            }  
  
            if (got_frame) {  
                pFrame->pts = av_frame_get_best_effort_timestamp(pFrame);  
                  
                /* push the decoded frame into the filtergraph */  
                if (av_buffersrc_add_frame(buffersrc_ctx, pFrame) < 0) {  
                    printf( "Error while feeding the filtergraph
");  
                    break;  
                }  
  
                /* pull filtered pictures from the filtergraph */  
                while (1) {  
  
                    ret = av_buffersink_get_frame(buffersink_ctx, pFrame_out);  
                    if (ret < 0)  
                        break;  
  
                    printf("Process 1 frame!
");  
  
                    if (pFrame_out->format==AV_PIX_FMT_YUV420P) {  
#if ENABLE_YUVFILE  
                        //Y, U, V  
                        for(int i=0;i<pFrame_out->height;i++){  
                            fwrite(pFrame_out->data[0]+pFrame_out->linesize[0]*i,1,pFrame_out->width,fp_yuv);  
                        }  
                        for(int i=0;i<pFrame_out->height/2;i++){  
                            fwrite(pFrame_out->data[1]+pFrame_out->linesize[1]*i,1,pFrame_out->width/2,fp_yuv);  
                        }  
                        for(int i=0;i<pFrame_out->height/2;i++){  
                            fwrite(pFrame_out->data[2]+pFrame_out->linesize[2]*i,1,pFrame_out->width/2,fp_yuv);  
                        }  
#endif  
                          
#if ENABLE_SDL  
                        SDL_LockYUVOverlay(bmp);  
                        int y_size=pFrame_out->width*pFrame_out->height;  
                        memcpy(bmp->pixels[0],pFrame_out->data[0],y_size);   //Y  
                        memcpy(bmp->pixels[2],pFrame_out->data[1],y_size/4); //U  
                        memcpy(bmp->pixels[1],pFrame_out->data[2],y_size/4); //V   
                        bmp->pitches[0]=pFrame_out->linesize[0];  
                        bmp->pitches[2]=pFrame_out->linesize[1];     
                        bmp->pitches[1]=pFrame_out->linesize[2];  
                        SDL_UnlockYUVOverlay(bmp);   
                        rect.x = 0;      
                        rect.y = 0;      
                        rect.w = pFrame_out->width;      
                        rect.h = pFrame_out->height;      
                        SDL_DisplayYUVOverlay(bmp, &rect);   
                        //Delay 40ms  
                        SDL_Delay(40);  
#endif  
                    }  
                    av_frame_unref(pFrame_out);  
                }  
            }  
            av_frame_unref(pFrame);  
        }  
        av_free_packet(&packet);  
    }  
#if ENABLE_YUVFILE  
    fclose(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));  
        printf("Error occurred: %s
", buf);  
        return -1;  
    }  
  
    return 0;  
}  

　　

结果

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。

原文链接：http://blog.csdn.net/leixiaohua1020/article/details/29368911