基于FFMPEG的视频解码

#include <stdio.h>
#include <cv.h>
#include <highgui.h>
#include <cvaux.h>


extern "C"
{
#include <libavcodec/avcodec.h>
#include <libavformat/avformat.h>
#include <libswscale/swscale.h>
};


const char *fileName = "D:\\video\\1.avi";

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;

int myDecodec(const char *fileName)
{
    // Register all formats and codecs
    // 初始化ffmpeg库
    av_register_all();

    // Open video file
    if(av_open_input_file(&pFormatCtx, fileName, NULL, 0, NULL)!=0)
    //  return -1; // 
    printf("Couldn't open 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
    printf("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, fileName, 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
    printf("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;

    IplImage *img = cvCreateImage(cvSize(pCodecCtx->width,pCodecCtx->height),8,3);

    // 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);
    */
    img_convert_ctx = sws_getContext(pCodecCtx->width,pCodecCtx->height, pCodecCtx->pix_fmt, 
            img->width, img->height, PIX_FMT_BGR24,SWS_BILINEAR, 0, 0, 0);

    if(img_convert_ctx == NULL)
    {
        fprintf(stderr, "Cannot initialize the conversion context!\n");
//      exit(1);
//      return -1;
        printf("Cannot initialize the conversion context!");
    }

    // 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
        printf("Codec not found");
    }
    // Open codec
    // 打开解码器
    if(avcodec_open(pCodecCtx, pCodec)<0)
    //  return -1; // Could not open codec
    printf("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;
    printf("Could not get frame !");

    // 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); 

                int linesize[4] = { img->widthStep, 0, 0, 0 };
                sws_scale(img_convert_ctx, pFrame->data, pFrame->linesize, 0, pCodecCtx->height,
                    (uint8_t **) & (img->imageData), linesize);

                /*cvSaveImage("img.bmp",image);*/
                // Save the frame to disk
                // 保存前5帧
                //if(++i<=15)
                //{
                //  /*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);
                //}
            }
        }

        cvShowImage("image",img);
        cvWaitKey(1);

        //---------------------  processing  -------------------




        // 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;
}

int main(){
    int err = myDecodec(fileName);
}
基于FFMPEG的视频解码

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