AVFrame的data和linesize：

YUV: linesize[0] =  width + padding size(16+16),linesize[1]=linesize[0]/2

        data[0],data[1],data[2]分别代表yuv 

RGB: linesize[0] = width*pixel_size  for RGB
        data[0]为packet rgb

AVFrame* pFrame;                   // Frame  
AVCodecContext* pContext;          // Codec Context 
int nUsedBytes = avcodec_decode_video(pContext, pFrame,  &nFrame, pSrcBuffer, nSrcLength); 
if(nUsedBytes > 0) 
{ 
    AVFrame  out_pic; 
    SwsContext* img_convert_ctx = sws_getContext(pContext->width, pContext->height
, pContext->pix_fmt, nDestW, nDestH,(PixelFormat)PIX_FMT_BGR24,SWS_BICUBIC, NULL, NULL, NULL); 
    if(img_convert_ctx != NULL) 
    { 
        if(avpicture_alloc((AVPicture *)&out_pic, PIX_FMT_RGB24, nDestW, nDestH)>=0) 
        { 
            pFrame->data[0] = pFrame->data[0]+pFrame->linesize[0]*(pContext->height-1); 
            pFrame->data[1] = pFrame->data[1]+pFrame->linesize[0]*pContext->height/4-1; 
       pFrame->data[2] = pFrame->data[2]+pFrame->linesize[0]*pContext->height/4-1; 
            pFrame->linesize[0] *= -1; 
            pFrame->linesize[1] *= -1; 
       pFrame->linesize[2] *= -1; 
       sws_scale(img_convert_ctx, pFrame->data, pFrame->linesize, 0, pContext->height
, out_pic.data, out_pic.linesize); 
            avpicture_free((AVPicture *)&out_pic); 
        } 
        sws_freeContext(img_convert_ctx); 
    } 
}