采用FFmpeg解帧，并保持到JPG格式文件
其实研究这个的目的主要是今后给Java项目使用。好久没看C了，公司业务大部分都是编解码视频的，带着一股冲动研究了一下。懂得了一点皮毛。
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首先下载ffmpeg的开发包以及依赖包，当然也可以下载源码。
http://ffmpeg.zeranoe.com/builds/
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其次为了编码为JPEG格式的图片，需要下载Independent JPEG Group
http://www.ijg.org/files/jpegsr9.zip
下载IJG后，需要对源码进行编译，生成静态库，
本人是使用VS2010编译的，其中含有install.txt文件讲述了怎么讲make file文件转换为VS工程文件，使用下面命令可以做到：
NMAKE /f makefile.vc ?setup-v10
其中会遇到windows环境变量中没有NMAKE?的问题，还有Win32.Mak找不到的问题。
1、找到nmake.exe配一下环境变量
2、在makefile.vc文件中找到Win32.Mak，将相应路径添加上，如：
!include <C:\Program Files\Microsoft SDKs\Windows\v7.0A\Include\Win32.Mak>
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#include <math.h>#include <windows.h>#include <libavutil/opt.h>#include <libavcodec/avcodec.h>#include <libavutil/channel_layout.h>#include <libavutil/common.h>#include <libavutil/imgutils.h>#include <libavutil/mathematics.h>#include <libavutil/samplefmt.h>#include <libavformat/avformat.h>#include <libswscale/swscale.h>#include <jpeglib.h>#include <setjmp.h>#define inline __inline#define snprintf _snprintf#define INBUF_SIZE 4096#define AUDIO_INBUF_SIZE 20480#define AUDIO_REFILL_THRESH 4096#pragma comment (lib, "Ws2_32.lib") #pragma comment (lib, "avcodec.lib")#pragma comment (lib, "avdevice.lib")#pragma comment (lib, "avfilter.lib")#pragma comment (lib, "avformat.lib")#pragma comment (lib, "avutil.lib")#pragma comment (lib, "swresample.lib")#pragma comment (lib, "swscale.lib") #pragma comment(lib, "jpeg.lib")static void SaveFrame(AVFrame *pFrame, int width, int height, int iFrame);static void yuv420p_save(AVFrame *pFrame, int width, int height, int iFrame);static void bmp_save(AVFrame *pFrame, int width, int height, int iFrame);static void saveFrame_jpg(uint8_t *pRGBBuffer, int iFrame, int width, int height);int main(int argc, char **argv){AVFormatContext *pFormatCtx = NULL;char *fileName = "E:\\aa.rm";int i,videoStream;AVCodecContext *pCodecCtx;AVCodec *pCodec;AVFrame *pFrame;AVFrame *pFrameRGB;int numBytes;uint8_t *buffer;AVPacket packet;int frameFinished;struct SwsContext *img_convert_ctx = NULL; av_register_all();if(avformat_open_input(&pFormatCtx, fileName, NULL, NULL)!=0){printf("can not open");return -1;}if(avformat_find_stream_info(pFormatCtx, NULL) < 0){printf("can not find");return -1;}av_dump_format(pFormatCtx, -1, fileName, 0);videoStream = -1;for (i=0;i<pFormatCtx->nb_streams;i++){if( pFormatCtx->streams[i]->codec->codec_type == AVMEDIA_TYPE_VIDEO){videoStream = i;break;}}if ( videoStream == -1 ){printf("not find videoStream");return -1;}pCodecCtx = pFormatCtx->streams[videoStream]->codec;pCodec = avcodec_find_decoder(pCodecCtx->codec_id);if ( pCodec == NULL ){return -1;}if( avcodec_open2(pCodecCtx, pCodec, NULL) < 0 ){return -1;}pFrame = av_frame_alloc();if( pFrame == NULL ){return -1;}pFrameRGB = av_frame_alloc();if( pFrameRGB == NULL ){return -1;}numBytes = avpicture_get_size(PIX_FMT_BGR24, pCodecCtx->width, pCodecCtx->height);buffer = av_malloc(numBytes);avpicture_fill((AVPicture *)pFrameRGB, buffer, PIX_FMT_BGR24, pCodecCtx->width, pCodecCtx->height);img_convert_ctx = sws_getCachedContext(img_convert_ctx, pCodecCtx->width, pCodecCtx->height,pCodecCtx->pix_fmt, pCodecCtx->width, pCodecCtx->height, PIX_FMT_RGB24, SWS_BICUBIC, NULL, NULL, NULL);i = 0;while( av_read_frame(pFormatCtx, &packet) >= 0 ){if( packet.stream_index == videoStream ){avcodec_decode_video2(pCodecCtx, pFrame, &frameFinished, &packet);if ( frameFinished ){if (!img_convert_ctx ){fprintf(stderr, "Cannot initialize sws conversion context\n");exit(1);}sws_scale(img_convert_ctx, (const uint8_t* const*)pFrame->data, pFrame->linesize, 0, pCodecCtx->height,pFrameRGB->data, pFrameRGB->linesize);if(i++<5){//SaveFrame(pFrameRGB, pCodecCtx->width, pCodecCtx->height, i);//yuv420p_save(pFrameRGB, pCodecCtx->width, pCodecCtx->height, i);//bmp_save(pFrameRGB, pCodecCtx->width, pCodecCtx->height, i);saveFrame_jpg(pFrameRGB->data[0], i, pCodecCtx->width, pCodecCtx->height);}}}if(i > 5){break;}}av_free_packet(&packet);av_free(buffer);av_free(pFrame);av_free(pFrameRGB);avcodec_close(pCodecCtx);avformat_close_input(&pFormatCtx); return 0;}static void SaveFrame(AVFrame *pFrame, int width, int height, int iFrame){FILE *pFile;char szFilename[32];int y;sprintf(szFilename, "frame%d.jpg", iFrame);pFile = fopen(szFilename, "wb");if( !pFile ){return;}fprintf(pFile, "P6\n%d %d\n255\n", width, height);for ( y=0; y<height; y++ ){fwrite(pFrame->data[0] + y * pFrame->linesize[0], 1, width * 3, pFile);}fclose(pFile);}static void yuv420p_save(AVFrame *pFrame, int width, int height, int iFrame){int i = 0;FILE *pFile;char szFilename[32];int height_half = height / 2, width_half = width / 2;int y_wrap = pFrame->linesize[0];int u_wrap = pFrame->linesize[1];int v_wrap = pFrame->linesize[2];unsigned char *y_buf = pFrame->data[0];unsigned char *u_buf = pFrame->data[1];unsigned char *v_buf = pFrame->data[2];sprintf(szFilename, "frame%d.jpg", iFrame);pFile = fopen(szFilename, "wb");//save yfor (i = 0; i < height; i++)fwrite(y_buf + i * y_wrap, 1, width, pFile);fprintf(stderr, "===>save Y success\n");//save ufor (i = 0; i < height_half; i++)fwrite(u_buf + i * u_wrap, 1, width_half, pFile);fprintf(stderr, "===>save U success\n");//save vfor (i = 0; i < height_half; i++)fwrite(v_buf + i * v_wrap, 1, width_half, pFile);fprintf(stderr, "===>save V success\n");fflush(pFile);fclose(pFile);}static void bmp_save(AVFrame *pFrame, int width, int height, int iFrame){BITMAPFILEHEADER bmpheader;BITMAPINFO bmpinfo;int y = 0;FILE *pFile;char szFilename[32];unsigned char *y_buf = pFrame->data[0];sprintf(szFilename, "frame%d.bmp", iFrame);pFile = fopen(szFilename, "wb");bmpheader.bfReserved1 = 0;bmpheader.bfReserved2 = 0;bmpheader.bfOffBits = sizeof(BITMAPFILEHEADER) + sizeof(BITMAPINFOHEADER);bmpheader.bfSize = bmpheader.bfOffBits + width*height*24/8;bmpinfo.bmiHeader.biSize = sizeof(BITMAPINFOHEADER);bmpinfo.bmiHeader.biWidth = width;bmpinfo.bmiHeader.biHeight = -height;bmpinfo.bmiHeader.biPlanes = 1;bmpinfo.bmiHeader.biBitCount = 24;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;fwrite(&bmpheader, sizeof(BITMAPFILEHEADER), 1, pFile);fwrite(&bmpinfo.bmiHeader, sizeof(BITMAPINFOHEADER), 1, pFile);fwrite(pFrame->data[0], width*height*24/8, 1, pFile);/*for(y=0; y<height; y++){fwrite(pFrame->data[0] + y*pFrame->linesize[0], 1, width*3, pFile);}*///fflush(pFile);fclose(pFile);}static void saveFrame_jpg(uint8_t *pRGBBuffer, int iFrame, int width, int height){struct jpeg_compress_struct cinfo;struct jpeg_error_mgr jerr;char szFilename[1024];int row_stride;FILE *fp;JSAMPROW row_pointer[1]; // 一行位图cinfo.err = jpeg_std_error(&jerr);jpeg_create_compress(&cinfo);sprintf(szFilename, "test%d.jpg", iFrame);//图片名字为视频名+号码fp = fopen(szFilename, "wb");if(fp == NULL) return;jpeg_stdio_dest(&cinfo, fp);cinfo.image_width = width; // 为图的宽和高，单位为像素 cinfo.image_height = height;cinfo.input_components = 3; // 在此为1,表示灰度图， 如果是彩色位图，则为3 cinfo.in_color_space = JCS_RGB; //JCS_GRAYSCALE表示灰度图，JCS_RGB表示彩色图像jpeg_set_defaults(&cinfo); jpeg_set_quality (&cinfo, 80, 1);jpeg_start_compress(&cinfo, TRUE);row_stride = cinfo.image_width * 3;//每一行的字节数,如果不是索引图,此处需要乘以3// 对每一行进行压缩while (cinfo.next_scanline < cinfo.image_height) {row_pointer[0] = &(pRGBBuffer[cinfo.next_scanline * row_stride]);jpeg_write_scanlines(&cinfo, row_pointer, 1);}jpeg_finish_compress(&cinfo);jpeg_destroy_compress(&cinfo);fclose(fp);}?
最后，将相应的lib和dll给链接上，以及头文件给添加好，应该没问题。
后续思考方向为如何添加自己的解码器，比如海康大华的SDK接入，封装dll给Java调用，希望更上一层楼吧。
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