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

转自：http://blog.csdn.net/skys_broyal/article/details/10337147

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

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#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

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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

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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);