FFMpeg学习笔记(2)

一个将视频流中帧转为BMP图片的例子.

代码如下：

#include "stdafx.h"
#include <string>
using namespace std;
#include <Windows.h>

extern "C"
{
#include "libavcodec/avcodec.h"
#include "libavformat/avformat.h"
#include "libswscale/swscale.h"
#pragma comment(lib, "avcodec.lib")
#pragma comment(lib, "avutil.lib")
#pragma comment(lib, "avformat.lib")
#pragma comment(lib, "swscale.lib")
}

string GetFilePath(string strFileName)
{
	char szPath[MAX_PATH];
	GetModuleFileNameA(NULL,szPath,MAX_PATH);
	char* pEnd = strrchr(szPath,'\\');
	*(pEnd+1) = '\0';
	string strPath = szPath;
	return strPath + strFileName;
}

void SaveFrameBMP(AVFrame* pFrame,int width,int height,int iFrame)  
{
	// 位图文件头  
	BITMAPFILEHEADER bmpheader;   
	BITMAPINFO bmpinfo;   
	int nBit = 24;
	int nSize = width*height*nBit/8;

	bmpheader.bfType = ('M' <<8)|'B';   
	bmpheader.bfReserved1 = 0;   
	bmpheader.bfReserved2 = 0;   
	bmpheader.bfOffBits = sizeof(BITMAPFILEHEADER) + sizeof(BITMAPINFOHEADER);   
	bmpheader.bfSize = bmpheader.bfOffBits + nSize;  

	bmpinfo.bmiHeader.biSize = sizeof(BITMAPINFOHEADER);   
	bmpinfo.bmiHeader.biWidth = width;   
	bmpinfo.bmiHeader.biHeight = 0-height;   
	bmpinfo.bmiHeader.biPlanes = 1;   
	bmpinfo.bmiHeader.biBitCount = nBit;   
	bmpinfo.bmiHeader.biCompression = BI_RGB;   
	bmpinfo.bmiHeader.biSizeImage = 0;   
	bmpinfo.bmiHeader.biXPelsPerMeter = 100;   
	bmpinfo.bmiHeader.biYPelsPerMeter = 100;   
	bmpinfo.bmiHeader.biClrUsed = 0;   
	bmpinfo.bmiHeader.biClrImportant = 0;  
	//
	char szFilename[32];
	sprintf_s(szFilename,sizeof(szFilename),"frame%d.BMP",iFrame);
	string strFrameName = GetFilePath(szFilename);
	FILE* pFile = NULL;
	fopen_s(&pFile,strFrameName.c_str(),"wb");
	if(pFile == NULL)
		return;
	fwrite(&bmpheader,sizeof(BITMAPFILEHEADER),1,pFile);   
	fwrite(&bmpinfo.bmiHeader,sizeof(BITMAPINFOHEADER),1,pFile);  
	fwrite(pFrame->data[0],nSize,1,pFile);
	fclose(pFile);  
}

int _tmain(int argc, _TCHAR* argv[])
{
	string strFileName = GetFilePath("test.mp4");
	//初始化，注册所有基于FFMpeg的编码器
	av_register_all();
	//打开视频流文件，获取头
	AVFormatContext* pFormatCtx = NULL;
	if(avformat_open_input(&pFormatCtx,strFileName.c_str(),NULL,NULL) != 0)
	{
		printf("av_open_input_file error.");
		return -1;
	}
	//获取视频流信息
	if(av_find_stream_info(pFormatCtx) < 0)
	{
		printf("av_find_stream_info error.");
		return -1;
	}
	//获取其他信息
	av_dump_format(pFormatCtx,0,strFileName.c_str(),0);
	//查找视频流
	int nVideoStream =-1;
	for(unsigned int i = 0;i < pFormatCtx->nb_streams;i++)
	{
		if(pFormatCtx->streams[i]->codec->codec_type == AVMEDIA_TYPE_VIDEO) 
		{
			nVideoStream = i;
			break;
		}
	}
	if(nVideoStream == -1)
	{
		printf("nVideoStream == -1 error.");
		return -1; // Didn't find a video stream
	}
	//获取视频流信息指针
	AVCodecContext* pCodecCtx = pFormatCtx->streams[nVideoStream]->codec;
	//查找视频流解码器
	AVCodec* pCodec = avcodec_find_decoder(pCodecCtx->codec_id);
	if(pCodec == NULL)
	{
		printf("avcodec_find_decoder error.");
		return -1; // Codec not found
	}
	//打开解码器
	if(avcodec_open(pCodecCtx,pCodec) < 0)
	{
		printf("avcodec_open error.");
		return -1;
	}
	//
	int nCount = 0;
	//用于保存解码前的视频数据帧
	AVFrame* pFrame = avcodec_alloc_frame();
	//用于保存解码后的视频数据帧
	AVFrame* pFrameRGB = avcodec_alloc_frame();
	int numBytes = avpicture_get_size(AV_PIX_FMT_RGB24,pCodecCtx->width,pCodecCtx->height);
	uint8_t* buffer = (uint8_t*)av_malloc(numBytes*sizeof(uint8_t));
	avpicture_fill((AVPicture *)pFrameRGB,buffer,AV_PIX_FMT_RGB24,pCodecCtx->width, pCodecCtx->height);
	//用于解码后数据格式转换
	SwsContext* pSwsCtx = sws_getContext(pCodecCtx->width,pCodecCtx->height,pCodecCtx->pix_fmt,pCodecCtx->width,pCodecCtx->height,AV_PIX_FMT_RGB24,SWS_BICUBIC,NULL, NULL, NULL);
	AVPacket packet;
	while(av_read_frame(pFormatCtx,&packet)>=0) 
	{
		//当前读取的数据流是否为视频流数据
		if(packet.stream_index == nVideoStream) 
		{
			//是否一帧已经完成
			int frameFinished;
			//解码视频流数据
			avcodec_decode_video2(pCodecCtx,pFrame,&frameFinished,&packet);   //
			if(frameFinished) 
			{ //视频流转换
				sws_scale(pSwsCtx,pFrame->data,pFrame->linesize,0,pCodecCtx->height,pFrameRGB->data, pFrameRGB->linesize);
				if(nCount <= 5)
				{
					SaveFrameBMP(pFrameRGB,pCodecCtx->width,pCodecCtx->height,nCount);
				}
				++nCount;
			}
		}
		av_free_packet(&packet);
	}
	//释放
	sws_freeContext(pSwsCtx);
	av_free(buffer);
	av_free(pFrameRGB);
	av_free(pFrame);
	avcodec_close(pCodecCtx);
	av_close_input_file(pFormatCtx);
	return 0;
}