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);
}