FFmpeg视频解码为逐帧数据

/************************************************************************ * Copyright(c) 2012 Yang Xian * All rights reserved. * * File: VideoDecode.cpp * Brief: 视频解码，并把解码后的RGB视频帧保存 * Version: 1.0 * Author: Yang Xian * Email: yang_xian521@163.com * Date: 2012/06/28 * History: ************************************************************************/ #include <stdio.h> extern "C" { #include <libavcodec/avcodec.h> #include <libavformat/avformat.h> #include <libswscale/swscale.h> }; 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) 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); // Close file fclose(pFile); } int main(int argc, char *argv[]) { AVFormatContext *pFormatCtx; int i, videoStream; AVCodecContext *pCodecCtx; AVCodec *pCodec; AVFrame *pFrame; AVFrame *pFrameRGB; AVPacket packet; int frameFinished; int numBytes; uint8_t *buffer; struct SwsContext *img_convert_ctx; if(argc < 2) { printf("Please provide a movie file\n"); return -1; } // Register all formats and codecs // 初始化ffmpeg库 av_register_all(); // Open video file if(av_open_input_file(&pFormatCtx, argv[1], NULL, 0, NULL)!=0) return -1; // Couldn't open file // Retrieve stream information // 查找文件的流信息 if(av_find_stream_info(pFormatCtx)<0) return -1; // Couldn't find stream information // Dump information about file onto standard error // dump只是一个调试函数，输出文件的音、视频流的基本信息：帧率、分辨率、音频采样等等 dump_format(pFormatCtx, 0, argv[1], 0); // Find the first video stream // 遍历文件的流，找到第一个视频流，并记录流的编码信息 videoStream=-1; for(i=0; i<pFormatCtx->nb_streams; i++) { if(pFormatCtx->streams[i]->codec->codec_type==CODEC_TYPE_VIDEO) { videoStream=i; break; } } if(videoStream==-1) return -1; // Didn't find a video stream // Get a pointer to the codec context for the video stream // 得到视频流编码的上下文指针 pCodecCtx=pFormatCtx->streams[videoStream]->codec; // construct the scale context, conversing to PIX_FMT_RGB24 // 根据编码信息设置渲染格式 img_convert_ctx = sws_getContext(pCodecCtx->width, pCodecCtx->height, pCodecCtx->pix_fmt, pCodecCtx->width, pCodecCtx->height, PIX_FMT_RGB24, SWS_BICUBIC, NULL, NULL, NULL); if(img_convert_ctx == NULL) { fprintf(stderr, "Cannot initialize the conversion context!\n"); // exit(1); return -1; } // Find the decoder for the video stream // 在库里面查找支持该格式的解码器 pCodec=avcodec_find_decoder(pCodecCtx->codec_id); if(pCodec==NULL) { fprintf(stderr, "Unsupported codec!\n"); return -1; // Codec not found } // Open codec // 打开解码器 if(avcodec_open(pCodecCtx, pCodec)<0) return -1; // Could not open codec // Allocate video frame // 分配一个帧指针，指向解码后的原始帧 pFrame=avcodec_alloc_frame(); // Allocate an AVFrame structure // 分配一个帧指针，指向存放转换成rgb后的帧 pFrameRGB=avcodec_alloc_frame(); if(pFrameRGB==NULL) return -1; // Determine required buffer size and allocate buffer numBytes=avpicture_get_size(PIX_FMT_RGB24, pCodecCtx->width, pCodecCtx->height); buffer=(uint8_t *)av_malloc(numBytes*sizeof(uint8_t)); // buffer = new uint8_t[numBytes]; // Assign appropriate parts of buffer to image planes in pFrameRGB // Note that pFrameRGB is an AVFrame, but AVFrame is a superset // of AVPicture // 给pFrameRGB帧附加上分配的内存 avpicture_fill((AVPicture *)pFrameRGB, buffer, PIX_FMT_RGB24, pCodecCtx->width, pCodecCtx->height); // Read frames and save first five frames to disk i=0; while(av_read_frame(pFormatCtx, &packet)>=0) // 读取一个帧 { // Is this a packet from the video stream? if(packet.stream_index==videoStream) { // Decode video frame // 解码该帧 avcodec_decode_video(pCodecCtx, pFrame, &frameFinished, packet.data, packet.size); // Did we get a video frame? if(frameFinished) { // Convert the image from its native format to RGB // img_convert((AVPicture *)pFrameRGB, PIX_FMT_RGB24, // (AVPicture*)pFrame, pCodecCtx->pix_fmt, pCodecCtx->width, // pCodecCtx->height); // 把该帧转换成rgb // 如果只提取关键帧，加上这句 // if (pFrame->key_frame == 1) sws_scale(img_convert_ctx, pFrame->data, pFrame->linesize, 0, pCodecCtx->height, pFrameRGB->data, pFrameRGB->linesize); // Save the frame to disk // 保存前5帧 if(++i<=5) { // char pic[200]; // sprintf(pic,"pic%d.bmp",i); // av_create_bmp(pic, pFrameRGB->data[0], pCodecCtx->width, pCodecCtx->height, 24); SaveFrame(pFrameRGB, pCodecCtx->width, pCodecCtx->height, i); } } } // Free the packet that was allocated by av_read_frame // 释放读取的帧内存 av_free_packet(&packet); } // 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 av_close_input_file(pFormatCtx); return 0; }