使用ffmpeg进行图像格式转换以及图像缩放/sws_scale/linux/c++/c/rgb-yuv420

  利用ffmpeg进行图像数据格式的转换以及图片的缩放应用中，主要用到了swscale.h文件中的三个函数，分别是：

      struct SwsContext *sws_getContext(int srcW, int srcH, enum AVPixelFormat srcFormat,
                               int dstW, int dstH, enum AVPixelFormat dstFormat,
                               int flags, SwsFilter *srcFilter,
                               SwsFilter *dstFilter, const double *param);

      int sws_scale(struct SwsContext *c, const uint8_t *const srcSlice[],

                     const int srcStride[], int srcSliceY, int srcSliceH,
                   uint8_t *const dst[], const int dstStride[]);

      void sws_freeContext(struct SwsContext *swsContext);

  sws_getContext函数可以看做是初始化函数，它的参数定义分别为：

      int srcW，int srcH 为原始图像数据的高和宽；

      int dstW，int dstH 为输出图像数据的高和宽；

      enum AVPixelFormat srcFormat 为输入和输出图片数据的类型；eg：AV_PIX_FMT_YUV420、PAV_PIX_FMT_RGB24；

      int flags 为scale算法种类；eg：SWS_BICUBIC、SWS_BICUBLIN、SWS_POINT、SWS_SINC；

      SwsFilter *srcFilter ，SwsFilter *dstFilter，const double *param 可以不用管，全为NULL即可；

  sws_scale函数则为执行函数，它的参数定义分别为：

      struct SwsContext *c 为sws_getContext函数返回的值；

      const uint8_t *const srcSlice[]，uint8_t *const dst[] 为输入输出图像数据各颜色通道的buffer指针数组；

      const int srcStride[]，const int dstStride[] 为输入输出图像数据各颜色通道每行存储的字节数数组；     

      int srcSliceY 为从输入图像数据的第多少列开始逐行扫描，通常设为0；

      int srcSliceH 为需要扫描多少行，通常为输入图像数据的高度；

  sws_freeContext函数为结束函数，它的参数即为sws_getContext函数返回的值；

  示例代码：rgb24_2_rgb24/1600*1200—352*288

//.h

#ifndef INT64_C#define INT64_C#define UINT64_C#endifextern "C"{#include "libswscale/swscale.h"}struct ImgInfo{    unsigned int height;    unsigned int width;    unsigned long bufferSize;    unsigned char *bufferPtr;}rawDate;

//.cpp

    int nSrcH = rawData.height;  //1200    int nSrcW = rawData.width;   //1600    int nDstH = RESIZED_HIGHT;   //258    int nDstW = RESIZED_WIDTH;   //352    uint8_t *pSrcBuff[3] = {rawData.bufferPtr, rawData.bufferPtr  + nSrcW * nSrcH, rawData.bufferPtr  + nSrcW * nSrcH * 2};    uint8_t *pDstBuff[3] = {pResizedData->bufferPtr, pResizedData->bufferPtr + nDstW * nDstH, pResizedData->bufferPtr + nDstW * nDstH * 2};           int nSrcStride[3];    int nDstStride[3];        for (int i=0; i<3; i++)    {    nSrcStride[i] = nSrcW * 3;    nDstStride[i] = nDstW * 3;    }        SwsContext*m_pSwsContext;        m_pSwsContext = sws_getContext(nSrcW, nSrcH, AV_PIX_FMT_RGB24,                                  nDstW, nDstH, AV_PIX_FMT_RGB24,                                  SWS_SINC,                                   NULL, NULL, NULL);                                      if (NULL == m_pSwsContext)     {    printf("ffmpeg get context error!\n");    return false;    }        sws_scale(m_pSwsContext, pSrcBuff,              nSrcStride, 0, nSrcH,              pDstBuff, nDstStride);                  sws_freeContext(m_pSwsContext);

示例代码：rgb24_2_yuv420/1600*1200—352*288

//.cpp

    int nSrcH = rawData->height;   //1200    int nSrcW = rawData->width;    //1600    int nDstH = RESIZED_HIGHT;    //288    int nDstW = RESIZED_WIDTH;    //352    uint8_t *pSrcBuff[3] = {rawData->bufferPtr, rawData->bufferPtr  + nSrcW * nSrcH, rawData->bufferPtr  + nSrcW * nSrcH * 2};    uint8_t *pDstBuff[3] = {resizedYuvData->bufferPtr, resizedYuvData->bufferPtr + nDstW * nDstH, resizedYuvData->bufferPtr + nDstW * nDstH * 5 / 4};           int nSrcStride[3];    int nDstStride[3];        for (int i=0; i<3; i++)    {    nSrcStride[i] = nSrcW * 3;    }        nDstStride[0] = nDstW;    nDstStride[1] = nDstW / 2;    nDstStride[2] = nDstW / 2;        SwsContext*m_pSwsContext;        m_pSwsContext = sws_getContext(nSrcW, nSrcH, AV_PIX_FMT_RGB24,                                  nDstW, nDstH, AV_PIX_FMT_YUV420P,                                  SWS_SINC,                                   NULL, NULL, NULL);                                      if (NULL == m_pSwsContext)     {    printf("ffmpeg get context error!\n");    return false;    }        sws_scale(m_pSwsContext, pSrcBuff,              nSrcStride, 0, nSrcH,              pDstBuff, nDstStride);                  sws_freeContext(m_pSwsContext);