FFMPEG读取关键帧（c++）

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FFMPEG读取关键帧（c++）

设法使用 av_read_frame 获得所有框架，其中逐帧地顺序读取，再用AVFrame-> key_frame判断关键帧，将其进行保存。

主要提取代码如下：

//获得帧图大小      PictureSize = avpicture_get_size(AV_PIX_FMT_BGR24, pCodecCtx->width, pCodecCtx->height);    buf = (uint8_t*)av_malloc(PictureSize);    if (buf == NULL) {        printf("av malloc failed!\n");        system("pause");        exit(1);    }    avpicture_fill((AVPicture *)pFrameRGB, buf, AV_PIX_FMT_BGR24, pCodecCtx->width, pCodecCtx->height);    //设置图像转换上下文      pSwsCtx = sws_getContext(pCodecCtx->width, pCodecCtx->height, pCodecCtx->pix_fmt, pCodecCtx->width, pCodecCtx->height, AV_PIX_FMT_BGR24, SWS_BICUBIC, NULL, NULL, NULL);    i = 0;    while (av_read_frame(pFormatCtx, &packet) >= 0) {        if (packet.stream_index == videoStream) {                       //解码                    avcodec_decode_video2(pCodecCtx, pFrame, &frameFinished, &packet);                  if (frameFinished) {                if (pFrame->key_frame) {                    //转换图像格式，将解压出来的YUV420P的图像转换为BRG24的图像                      sws_scale(pSwsCtx, (const uint8_t* const*)pFrame->data, pFrame->linesize, 0, pCodecCtx->height, pFrameRGB->data, pFrameRGB->linesize);                    //保存为bmp图                      SaveAsBMP(pFrameRGB, pCodecCtx->width, pCodecCtx->height, i, 24);                    i++;                }                           }            av_free_packet(&packet);        }    }

注意① ffmpeg 中的函数 av_read_frame 是用来完成解封装的过程，它会从码流里面提取每一个音频、视频帧，它使用了结构体 AVPacket 来记录每一帧的信息。

AVPacket avpkt;av_init_packet(&avpkt);while (!interrupt) {    int ret = av_read_frame(ic, &avpkt);    if (ret < 0) {        break;    }    // processing}av_free_packet(&avpkt);

每循环一次，就从码流中解封装并且提取了一帧数据，并存放在了 AVPacket 结构体中。

注意② 用 AVPacket 的成员变量stream_index判断Packet 到底是音频还是视频：

int video_stream_idx = av_find_best_stream(ic, AVMEDIA_TYPE_VIDEO, -1, -1, NULL, 0);int audio_stream_idx = av_find_best_stream(ic, AVMEDIA_TYPE_AUDIO, -1, -1, NULL, 0);if (avpkt.stream_index == video_stream_idx) {    LOGD("read a video frame");} else if (avpkt.stream_index == audio_stream_idx) {    LOGD("read audio frame);}

读取视频文件，提取关键帧并保存关键帧代码如下：

#include "stdafx.h"#include <windows.h>#include <WinGDI.h>#include <iostream>#include <iosfwd>#include <fstream>#define __STDC_CONSTANT_MACROSextern "C"{    #include <libavcodec/avcodec.h>//处理原始音频和视频流的解码    #include <libavutil/opt.h>    #include <libavutil/channel_layout.h>    #include <libavutil/common.h>    #include <libavutil/imgutils.h>    #include <libavutil/mathematics.h>    #include <libavutil/samplefmt.h>    #include <libavformat/avformat.h>//处理解析视频文件并将包含在其中的流分离出来    #include <libswscale/swscale.h>    #include <libavutil/imgutils.h>    #include <libavutil/parseutils.h>}#pragma comment(lib,"avcodec.lib")#pragma comment(lib,"avdevice.lib")#pragma comment(lib,"avfilter.lib")#pragma comment(lib,"avformat.lib")#pragma comment(lib,"avutil.lib")#pragma comment(lib,"swscale.lib")#pragma comment(lib,"postproc.lib")#pragma comment(lib,"swresample.lib")using namespace std;//定义BMP文件头   #ifndef _WINGDI_    #define _WINGDI_    typedef struct tagBITMAPFILEHEADER {    WORD    bfType;    DWORD   bfSize;    WORD    bfReserved1;    WORD    bfReserved2;    DWORD   bfOffBits;} BITMAPFILEHEADER, FAR *LPBITMAPFILEHEADER, *PBITMAPFILEHEADER;typedef struct tagBITMAPINFOHEADER {    DWORD      biSize;    LONG       biWidth;    LONG       biHeight;    WORD       biPlanes;    WORD       biBitCount;    DWORD      biCompression;    DWORD      biSizeImage;    LONG       biXPelsPerMeter;    LONG       biYPelsPerMeter;    DWORD      biClrUsed;    DWORD      biClrImportant;} BITMAPINFOHEADER, FAR *LPBITMAPINFOHEADER, *PBITMAPINFOHEADER;#endif      //保存BMP文件的函数    void SaveAsBMP(AVFrame *pFrameRGB, int width, int height, int index, int bpp){    char buf[5] = { 0 };   //bmp头         BITMAPFILEHEADER bmpheader;    BITMAPINFOHEADER bmpinfo;    FILE *fp;    char *filename = new char[255];  //文件存放路径，根据自己的修改         sprintf_s(filename, 255, "%s_%d.bmp", "E:/ffmpeg/keyFrame/", index);    if ((fp = fopen(filename, "wb+")) == NULL) {        printf("open file failed!\n");        return;    }    bmpheader.bfType = 0x4d42;    bmpheader.bfReserved1 = 0;    bmpheader.bfReserved2 = 0;    bmpheader.bfOffBits = sizeof(BITMAPFILEHEADER) + sizeof(BITMAPINFOHEADER);    bmpheader.bfSize = bmpheader.bfOffBits + width*height*bpp / 8;    bmpinfo.biSize = sizeof(BITMAPINFOHEADER);    bmpinfo.biWidth = width;    bmpinfo.biHeight = -height;    bmpinfo.biPlanes = 1;    bmpinfo.biBitCount = bpp;    bmpinfo.biCompression = BI_RGB;    bmpinfo.biSizeImage = (width*bpp + 31) / 32 * 4 * height;    bmpinfo.biXPelsPerMeter = 100;    bmpinfo.biYPelsPerMeter = 100;    bmpinfo.biClrUsed = 0;    bmpinfo.biClrImportant = 0;    fwrite(&bmpheader, sizeof(bmpheader), 1, fp);    fwrite(&bmpinfo, sizeof(bmpinfo), 1, fp);    fwrite(pFrameRGB->data[0], width*height*bpp / 8, 1, fp);    fclose(fp);}int main(){    //printf("%d\n", avcodec_version());    unsigned int i = 0, videoStream = -1;    AVFormatContext *pFormatCtx;    AVCodecContext *pCodecCtx;    AVCodec *pCodec;    AVFrame *pFrame, *pFrameRGB;    struct SwsContext *pSwsCtx;    const char *filename = "E:/ffmpeg/中国合伙人.flv";    int frameFinished;    int PictureSize;    AVPacket packet;    uint8_t *buf;    //注册解码器      av_register_all();    avformat_network_init();    pFormatCtx = avformat_alloc_context();    //AVInputFormat *pInputFormt = av_find_input_format("dshow");      if (avformat_open_input(&pFormatCtx, filename, NULL, NULL) != 0) {        printf("%s\n", "failed");        system("pause");    }    //获取视频流信息      if (avformat_find_stream_info(pFormatCtx, NULL)<0) {        printf("%s\n", "couldn`t find stream info");        system("pause");    }    //获取视频数据      for (int i = 0; i<pFormatCtx->nb_streams; i++)        if (pFormatCtx->streams[i]->codec->codec_type == AVMEDIA_TYPE_VIDEO) {            //AVMEDIA_TYPE_VIDEO            //AV_CODEC_ID_H264            videoStream = i;        }    if (videoStream == -1) {        printf("%s\n", "find video stream failed");        system("pause");        exit(1);    }    pCodecCtx = pFormatCtx->streams[videoStream]->codec;    pCodec = avcodec_find_decoder(pCodecCtx->codec_id);    if (pCodec == NULL) {        printf("%d\n", "avcode find decoder failed!");        system("pause");        exit(1);    }    //打开解码器      if (avcodec_open2(pCodecCtx, pCodec, NULL)<0) {        printf("avcode open failed!\n");        system("pause");        exit(1);    }    //为每帧图像分配内存      pFrame = av_frame_alloc();    pFrameRGB = av_frame_alloc();    if (pFrame == NULL || pFrameRGB == NULL) {        printf("av frame alloc failed!\n");        system("pause");        exit(1);    }    //获得帧图大小      PictureSize = avpicture_get_size(AV_PIX_FMT_BGR24, pCodecCtx->width, pCodecCtx->height);    buf = (uint8_t*)av_malloc(PictureSize);    if (buf == NULL) {        printf("av malloc failed!\n");        system("pause");        exit(1);    }    avpicture_fill((AVPicture *)pFrameRGB, buf, AV_PIX_FMT_BGR24, pCodecCtx->width, pCodecCtx->height);    //设置图像转换上下文      pSwsCtx = sws_getContext(pCodecCtx->width, pCodecCtx->height, pCodecCtx->pix_fmt, pCodecCtx->width, pCodecCtx->height, AV_PIX_FMT_BGR24, SWS_BICUBIC, NULL, NULL, NULL);    i = 0;    while (av_read_frame(pFormatCtx, &packet) >= 0) {        if (packet.stream_index == videoStream) {                       //解码                        avcodec_decode_video2(pCodecCtx, pFrame, &frameFinished, &packet);                  if (frameFinished) {                if (pFrame->key_frame) {                    //转换图像格式，将解压出来的YUV420P的图像转换为BRG24的图像                      sws_scale(pSwsCtx, (const uint8_t* const*)pFrame->data, pFrame->linesize, 0, pCodecCtx->height, pFrameRGB->data, pFrameRGB->linesize);                    //保存为bmp图                      SaveAsBMP(pFrameRGB, pCodecCtx->width, pCodecCtx->height, i, 24);                    i++;                }                           }            av_free_packet(&packet);        }    }    sws_freeContext(pSwsCtx);    av_free(pFrame);    av_free(pFrameRGB);    avcodec_close(pCodecCtx);    avformat_close_input(&pFormatCtx);    printf("关键帧已保存在设置路径！\n");    system("pause");    return 0;}

运行效果：

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