ffmpeg 对图像数据格式以及图片缩放

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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_FAST_BILINEAR，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

[cpp] view plain copy    #ifndef INT64_C      #define INT64_C      #define UINT64_C      #endif      extern "C"      {      #include "libswscale/swscale.h"      }      struct ImgInfo      {          unsigned int height;          unsigned int width;          unsigned long bufferSize;          unsigned char *bufferPtr;      }rawDate;

//.cpp

[cpp] view plain copy    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[cpp] view plain copy    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);

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