ffmpeg2.8将多媒体文件保存为ppm

基于ffmpeg 2.8 API 的改写

////  main.cpp//  save_video_to_ppm////  Created by meitu on 15/10/15.//  Copyright © 2015年 meitu. All rights reserved.//#ifdef __cplusplusextern "C"{#endif#include "libavcodec/avcodec.h"#include "libavutil/imgutils.h"#include "libavformat/avformat.h"#include "libswscale/swscale.h"#ifdef __cplusplus}#endifstatic void SaveFrame(AVFrame* pFrame, int width, int height, int iFrame){    FILE *pFile;    char szFilename[32];    int y;    //Open file    sprintf(szFilename, "frame%d.ppm", iFrame);    pFile = fopen(szFilename, "wb");    if (pFile == NULL) {        fprintf(stderr, "Could not open the ppm file.\n");        return;    }    //Write header    fprintf(pFile, "P6\n%d %d\n255\n", width, height);    //Write pixel data    for (y = 0; y < height; ++y) {        fwrite(pFrame->data[0] + y*pFrame->linesize[0], 1, width*3, pFile);    }    fclose(pFile);}int main(int argc, char *argv[]){    av_register_all();    AVFormatContext *pFormatCtx = NULL;    //Open video file and allocate format context    //读取文件的头部信息，并且保持这些信息到AVFormatContext中    //如果AVFormatContext是NULL,这个函数将会同时申请一个空间    if (avformat_open_input(&pFormatCtx, argv[1], NULL, NULL) < 0) {        av_log(pFormatCtx, AV_LOG_ERROR, "Could not open file.\n");        return 1;    }    //检查在文件的流的信息    //这个函数为 pFormatCtx-streams填充正确的信息    if (avformat_find_stream_info(pFormatCtx, NULL) < 0) {        av_log(pFormatCtx, AV_LOG_ERROR, "Could not find stream info.\n");        return 1;    }    //输出信息    av_dump_format(pFormatCtx, 0, argv[1], 0);    //找到视频流    int videoStream = 0;    videoStream = av_find_best_stream(pFormatCtx, AVMEDIA_TYPE_VIDEO, -1, -1, NULL, 0);    if (videoStream == -1) {        av_log(pFormatCtx, AV_LOG_ERROR, "Could not find stream index.\n");        return 1;    }    AVCodecContext *pCodecCtx = NULL;    pCodecCtx = pFormatCtx->streams[videoStream]->codec;    AVCodec *pCodec = NULL;    pCodec =avcodec_find_decoder(pCodecCtx->codec_id);    if (pCodec == NULL) {        av_log(pCodec, AV_LOG_ERROR, "Could not find decoder.\n");        return 1;    }    //open codec    if (avcodec_open2(pCodecCtx, pCodec, NULL) < 0) {        av_log(pCodecCtx, AV_LOG_ERROR, "Could open decoder.\n");        return 1;    }    AVFrame *pFrameRGB = NULL;    pFrameRGB = av_frame_alloc();    if (!pFrameRGB) {        av_log(pFrameRGB , AV_LOG_ERROR, "Could allocate frame.\n");        return 1;    }    uint8_t *buffer;    int numBytes = 0;    /*        之前我们申请了一个 帧 对象，当转换的时候，我们仍然需要一个地方来放置原始的数据。        我们使用avpicture_get_size来获取大小，然后av_malloc申请大小        avpicture_fill将申请的帧和我们新申请的内存结合起来     *///    numBytes = avpicture_get_size(PIX_FMT_RGB24, pCodecCtx->width, pCodecCtx->height);//    buffer = (uint8_t *)av_malloc(numBytes);//    avpicture_fill((AVPicture*)pFrameRGB, buffer, PIX_FMT_RGB24, pCodecCtx->width, pCodecCtx->height);    //使用av_image_alloc代替上面注释的三行代码    av_image_alloc(pFrameRGB->data, pFrameRGB->linesize, pCodecCtx->width, pCodecCtx->height, PIX_FMT_RGB24, 1);    //接下来，读入整个视频流，然后把它解码成帧，最后转换格式并且保存    int frameFinished;    AVPacket pkt;    //用来存储解码后的原始数据    AVFrame *pFrame = av_frame_alloc();    int i = 0;    auto img_convert_ctx = sws_getContext(pCodecCtx->width, pCodecCtx->height, pCodecCtx->pix_fmt, pCodecCtx->width, pCodecCtx->height, PIX_FMT_RGB24, SWS_BILINEAR, NULL, NULL, NULL);    while (av_read_frame(pFormatCtx, &pkt) >= 0) {        //Is this a packet from the video stream?        if (pkt.stream_index == videoStream) {            //Decode video frame            //packet -----> frame            avcodec_decode_video2(pCodecCtx, pFrame, &frameFinished, &pkt);            if (frameFinished) {                sws_scale(img_convert_ctx, (const uint8_t* const*)pFrame->data, pFrame->linesize, 0, pCodecCtx->height, (uint8_t *const *)pFrameRGB->data, pFrameRGB->linesize);                if( ++i <= 100 )                    SaveFrame(pFrameRGB, pCodecCtx->width, pCodecCtx->height, i);            }            av_free_packet(&pkt);        }    }    sws_freeContext(img_convert_ctx);    //free the rgb image    //av_free(buffer);    av_free(pFrameRGB);    //free the yuv frame    av_free(pFrame);    //close the codec    avcodec_close(pCodecCtx);    //close the video file    avformat_close_input(&pFormatCtx);    return 0;}

一些具体的解释请看参考文献

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