ffmpeg：sws_scale在RGB到YUV420转换期间在平面V中返回错误的值

Question

I am trying to use sws_scale to transform an image from RGB to YUV420P. The code I use in C++ is the following:

SwsContext *swscontext = sws_getContext(current_width,
                                        current_height,
                                        PIX_FMT_RGB24,
                                        current_width,
                                        current_height,
                                        PIX_FMT_YUV420P,
                                        SWS_FAST_BILINEAR,
                                        NULL,
                                        NULL,
                                        NULL);
const int srcstride[3] = {current_width * 3, 0, 0};
BYTE *data_pos[3] = {data, NULL, NULL};
BYTE *dest[3] = {yuv,
                yuv + current_width * current_height,
                yuv + (current_width * current_height) 
                    + ((current_width * current_height) / 2)};
const int dststride[3] = {current_width, current_width / 2, current_width / 2};
sws_scale(swscontext, data_pos, srcstride, 0, current_height,
          dest, dststride);

The Y and U planes are encoded properly but the V plane is completely written with the value 0x80 I wonder if I am doing anything wrong.

Answer 1

I still have no idea of why it works, but this solved the problem:

BYTE *dest[3] = {yuv,
                 yuv + current_width * current_height,
                 yuv + (current_width * current_height) 
                     + ((current_width >> 1) * (current_height >> 1))};

Semantically they are the same, so I will leave this question open in case someone come up with an explanation.