AVI Generated From D3D11_MAPPED_SUBRESOURCE->pData is Blank - c++

Question

I have a simple C++ application on Windows that is using DirectX to capture the screen to a bitmap vector, stored in format like this, based on WinDesktopDup sample here :
struct Bitmap {
int Width = 0;
int Height = 0;
std::vector<uint8_t> Buf;
};
I am trying to write a collection of this captures to a video file. I am trying to write to an AVI file using Windows APIs
The Visual Studio 2019 project is here
An AVI file is being generated, but it's blank and while seems to be valid, playing in Windows 11's media player, and VLC, and doesn't have any content just black screens.
The screen capture is being performed on has a resolution of 3840 x 2160. Each frame is taking about 33 MB of RAM, which is not very efficient but at this stage my goal is to get something that works. I am running as x64 and have plenty of free memory.
After the AVI header in file, the file is just full of 0 byte values:
The main section of code here:
#include "stdafx.h"
#include "WinDesktopDup.h"
#include "WriteAVI.h"
int main()
{
WinDesktopDup desktopDup;
desktopDup.Initialize();
desktopDup.CaptureNext();
const int numberOfBitmaps = 60;
const int frameRatePerSecond = 2;
Bitmap bmp[numberOfBitmaps];
for (int i = 0; i < numberOfBitmaps; i++)
{
bmp[i].Width = desktopDup.Latest.Width;
bmp[i].Height = desktopDup.Latest.Height;
bmp[i].Buf.resize(desktopDup.Latest.Buf.size());
}
int counter = 0;
bool done = false;
while (!done)
{
printf("Capturing frame %i / %i\r\n", counter, numberOfBitmaps);
desktopDup.CaptureNext();
std::copy(desktopDup.Latest.Buf.begin(), desktopDup.Latest.Buf.end(), bmp[counter].Buf.begin());
counter++;
if (counter >= numberOfBitmaps)
{
counter = 0;
done = true;
}
//if <some event triggered> done = true;
Sleep(1000 / frameRatePerSecond);
}
printf("Writing to AVI ...\r\n");
// dump bitmaps to video
wchar_t fileName[] = L"C:\\support\\test.avi";
CAVIFile aviFile(fileName, desktopDup.Latest.Width, desktopDup.Latest.Height);
BITMAPINFO inf;
memset(&inf, 0, sizeof(inf));
inf.bmiHeader.biSize = sizeof(inf.bmiHeader);
inf.bmiHeader.biWidth = desktopDup.Latest.Width;
inf.bmiHeader.biHeight = -desktopDup.Latest.Height;
inf.bmiHeader.biPlanes = 1;
inf.bmiHeader.biBitCount = 32;
inf.bmiHeader.biCompression = BI_RGB;
void* bits = nullptr;
HDC srcDC = GetWindowDC(NULL);
for (int i = 0; i < numberOfBitmaps; i++)
{
HBITMAP dib = CreateDIBSection(srcDC, &inf, 0, &bits, nullptr, 0);
memcpy(bits, bmp[i].Buf.data(), bmp[i].Width * bmp[i].Height * 4);
for (int j = 0; j < (15 / frameRatePerSecond); j++)
{
aviFile.AddFrame(dib);
}
DeleteObject(dib);
}
DeleteObject(srcDC);
}