[c++] Fastest method of screen capturing on Windows

I want to write a screencasting program for the Windows platform, but am unsure of how to capture the screen. The only method I'm aware of is to use GDI, but I'm curious whether there are other ways to go about this, and, if there are, which incurs the least overhead? Speed is a priority.

The screencasting program will be for recording game footage, although, if this does narrow down the options, I'm still open for any other suggestions that fall out of this scope. Knowledge isn't bad, after all.

Edit: I came across this article: Various methods for capturing the screen. It has introduced me to the Windows Media API way of doing it and the DirectX way of doing it. It mentions in the Conclusion that disabling hardware acceleration could drastically improve the performance of the capture application. I'm curious as to why this is. Could anyone fill in the missing blanks for me?

Edit: I read that screencasting programs such as Camtasia use their own capture driver. Could someone give me an in-depth explanation on how it works, and why it is faster? I may also need guidance on implementing something like that, but I'm sure there is existing documentation anyway.

Also, I now know how FRAPS records the screen. It hooks the underlying graphics API to read from the back buffer. From what I understand, this is faster than reading from the front buffer, because you are reading from system RAM, rather than video RAM. You can read the article here.

This is what I use to collect single frames, but if you modify this and keep the two targets open all the time then you could "stream" it to disk using a static counter for the file name. - I can't recall where I found this, but it has been modified, thanks to whoever!

void dump_buffer()
{
   IDirect3DSurface9* pRenderTarget=NULL;
   IDirect3DSurface9* pDestTarget=NULL;
     const char file[] = "Pickture.bmp";
   // sanity checks.
   if (Device == NULL)
      return;

   // get the render target surface.
   HRESULT hr = Device->GetRenderTarget(0, &pRenderTarget);
   // get the current adapter display mode.
   //hr = pDirect3D->GetAdapterDisplayMode(D3DADAPTER_DEFAULT,&d3ddisplaymode);

   // create a destination surface.
   hr = Device->CreateOffscreenPlainSurface(DisplayMde.Width,
                         DisplayMde.Height,
                         DisplayMde.Format,
                         D3DPOOL_SYSTEMMEM,
                         &pDestTarget,
                         NULL);
   //copy the render target to the destination surface.
   hr = Device->GetRenderTargetData(pRenderTarget, pDestTarget);
   //save its contents to a bitmap file.
   hr = D3DXSaveSurfaceToFile(file,
                              D3DXIFF_BMP,
                              pDestTarget,
                              NULL,
                              NULL);

   // clean up.
   pRenderTarget->Release();
   pDestTarget->Release();
}

I wrote a class that implemented the GDI method for screen capture. I too wanted extra speed so, after discovering the DirectX method (via GetFrontBuffer) I tried that, expecting it to be faster.

I was dismayed to find that GDI performs about 2.5x faster. After 100 trials capturing my dual monitor display, the GDI implementation averaged 0.65s per screen capture, while the DirectX method averaged 1.72s. So GDI is definitely faster than GetFrontBuffer, according to my tests.

I was unable to get Brandrew's code working to test DirectX via GetRenderTargetData. The screen copy came out purely black. However, it could copy that blank screen super fast! I'll keep tinkering with that and hope to get a working version to see real results from it.

i myself do it with directx and think it's as fast as you would want it to be. i don't have a quick code sample, but i found this which should be useful. the directx11 version should not differ a lot, directx9 maybe a little more, but thats the way to go

With Windows 8, Microsoft introduced the Windows Desktop Duplication API. That is the officially recommended way of doing it. One nice feature it has for screencasting is that it detects window movement, so you can transmit block deltas when windows get moved around, instead of raw pixels. Also, it tells you which rectangles have changed, from one frame to the next.

The Microsoft example code is pretty complex, but the API is actually simple and easy to use. I've put together an example project which is much simpler than the official example:

https://github.com/bmharper/WindowsDesktopDuplicationSample

Docs: https://docs.microsoft.com/en-gb/windows/desktop/direct3ddxgi/desktop-dup-api

Microsoft official example code: https://code.msdn.microsoft.com/windowsdesktop/Desktop-Duplication-Sample-da4c696a

I wrote a video capture software, similar to FRAPS for DirectX applications. The source code is available and my article explains the general technique. Look at http://blog.nektra.com/main/2013/07/23/instrumenting-direct3d-applications-to-capture-video-and-calculate-frames-per-second/

Respect to your questions related to performance,

• DirectX should be faster than GDI except when you are reading from the frontbuffer which is very slow. My approach is similar to FRAPS (reading from backbuffer). I intercept a set of methods from Direct3D interfaces.

• For video recording in realtime (with minimal application impact), a fast codec is essential. FRAPS uses it's own lossless video codec. Lagarith and HUFFYUV are generic lossless video codecs designed for realtime applications. You should look at them if you want to output video files.

• Another approach to recording screencasts could be to write a Mirror Driver. According to Wikipedia: When video mirroring is active, each time the system draws to the primary video device at a location inside the mirrored area, a copy of the draw operation is executed on the mirrored video device in real-time. See mirror drivers at MSDN: http://msdn.microsoft.com/en-us/library/windows/hardware/ff568315(v=vs.85).aspx.

I use d3d9 to get the backbuffer, and save that to a png file using the d3dx library:

    IDirect3DSurface9 *surface ;

    // GetBackBuffer
    idirect3ddevice9->GetBackBuffer(0, 0, D3DBACKBUFFER_TYPE_MONO, &surface ) ;

    // save the surface
    D3DXSaveSurfaceToFileA( "filename.png", D3DXIFF_PNG, surface, NULL, NULL ) ;

    SAFE_RELEASE( surface ) ;

To do this you should create your swapbuffer with

d3dpps.SwapEffect = D3DSWAPEFFECT_COPY ; // for screenshots.

(So you guarantee the backbuffer isn't mangled before you take the screenshot).

A few things I've been able to glean: apparently using a "mirror driver" is fast though I'm not aware of an OSS one.

Why is RDP so fast compared to other remote control software?

Also apparently using some convolutions of StretchRect are faster than BitBlt

http://betterlogic.com/roger/2010/07/fast-screen-capture/comment-page-1/#comment-5193

And the one you mentioned (fraps hooking into the D3D dll's) is probably the only way for D3D applications, but won't work with Windows XP desktop capture. So now I just wish there were a fraps equivalent speed-wise for normal desktop windows...anybody?

(I think with aero you might be able to use fraps-like hooks, but XP users would be out of luck).

Also apparently changing screen bit depths and/or disabling hardware accel. might help (and/or disabling aero).

https://github.com/rdp/screen-capture-recorder-program includes a reasonably fast BitBlt based capture utility, and a benchmarker as part of its install, which can let you benchmark BitBlt speeds to optimize them.

VirtualDub also has an "opengl" screen capture module that is said to be fast and do things like change detection http://www.virtualdub.org/blog/pivot/entry.php?id=290

You can try the c++ open source project WinRobot @git, a powerful screen capturer

CComPtr<IWinRobotService> pService;
hr = pService.CoCreateInstance(__uuidof(ServiceHost) );

//get active console session
CComPtr<IUnknown> pUnk;
hr = pService->GetActiveConsoleSession(&pUnk);
CComQIPtr<IWinRobotSession> pSession = pUnk;

// capture screen
pUnk = 0;
hr = pSession->CreateScreenCapture(0,0,1280,800,&pUnk);

// get screen image data(with file mapping)
CComQIPtr<IScreenBufferStream> pBuffer = pUnk;

Support :

• UAC Window
• Winlogon
• DirectShowOverlay

For C++ you can use: http://www.pinvoke.net/default.aspx/gdi32/BitBlt.html
This may hower not work on all types of 3D applications/video apps. Then this link may be more useful as it describes 3 different methods you can use.

Old answer (C#):
You can use System.Drawing.Graphics.Copy, but it is not very fast.

A sample project I wrote doing exactly this: http://blog.tedd.no/index.php/2010/08/16/c-image-analysis-auto-gaming-with-source/

I'm planning to update this sample using a faster method like Direct3D: http://spazzarama.com/2009/02/07/screencapture-with-direct3d/

And here is a link for capturing to video: How to capture screen to be video using C# .Net?

In my Impression, the GDI approach and the DX approach are different in its nature. painting using GDI applies the FLUSH method, the FLUSH approach draws the frame then clear it and redraw another frame in the same buffer, this will result in flickering in games require high frame rate.

1. WHY DX quicker? in DX (or graphics world), a more mature method called double buffer rendering is applied, where two buffers are present, when present the front buffer to the hardware, you can render to the other buffer as well, then after the frame 1 is finished rendering, the system swap to the other buffer( locking it for presenting to hardware , and release the previous buffer ), in this way the rendering inefficiency is greatly improved.
2. WHY turning down hardware acceleration quicker? although with double buffer rendering, the FPS is improved, but the time for rendering is still limited. modern graphic hardware usually involves a lot of optimization during rendering typically like anti-aliasing, this is very computation intensive, if you don't require that high quality graphics, of course you can just disable this option. and this will save you some time.

I think what you really need is a replay system, which I totally agree with what people discussed.

EDIT: I can see that this is listed under your first edit link as "the GDI way". This is still a decent way to go even with the performance advisory on that site, you can get to 30fps easily I would think.

From this comment (I have no experience doing this, I'm just referencing someone who does):

HDC hdc = GetDC(NULL); // get the desktop device context
HDC hDest = CreateCompatibleDC(hdc); // create a device context to use yourself

// get the height and width of the screen
int height = GetSystemMetrics(SM_CYVIRTUALSCREEN);
int width = GetSystemMetrics(SM_CXVIRTUALSCREEN);

// create a bitmap
HBITMAP hbDesktop = CreateCompatibleBitmap( hdc, width, height);

// use the previously created device context with the bitmap
SelectObject(hDest, hbDesktop);

// copy from the desktop device context to the bitmap device context
// call this once per 'frame'
BitBlt(hDest, 0,0, width, height, hdc, 0, 0, SRCCOPY);

// after the recording is done, release the desktop context you got..
ReleaseDC(NULL, hdc);

// ..delete the bitmap you were using to capture frames..
DeleteObject(hbDesktop);

// ..and delete the context you created
DeleteDC(hDest);

I'm not saying this is the fastest, but the BitBlt operation is generally very fast if you're copying between compatible device contexts.

For reference, Open Broadcaster Software implements something like this as part of their "dc_capture" method, although rather than creating the destination context hDest using CreateCompatibleDC they use an IDXGISurface1, which works with DirectX 10+. If there is no support for this they fall back to CreateCompatibleDC.

To change it to use a specific application, you need to change the first line to GetDC(game) where game is the handle of the game's window, and then set the right height and width of the game's window too.

Once you have the pixels in hDest/hbDesktop, you still need to save it to a file, but if you're doing screen capture then I would think you would want to buffer a certain number of them in memory and save to the video file in chunks, so I will not point to code for saving a static image to disk.

DXGI Desktop Capture

Project that captures the desktop image with DXGI duplication. Saves the captured image to the file in different image formats (*.bmp; *.jpg; *.tif).

This sample is written in C++. You also need some experience with DirectX (D3D11, D2D1).

What the Application Can Do

• If you have more than one desktop monitor, you can choose.
• Resize the captured desktop image.
• Choose different scaling modes.
• You can show or hide the mouse icon in the output image.
• You can rotate the image for the output picture, or leave it as default.

Screen Recording can be done in C# using VLC API. I have done a sample program to demonstrate this. It uses LibVLCSharp and VideoLAN.LibVLC.Windows libraries. You could achieve many more features related to video rendering using this cross platform API.

For API documentation see: LibVLCSharp API Github

using System;
using System.IO;
using System.Reflection;
using System.Threading;
using LibVLCSharp.Shared;

namespace ScreenRecorderNetApp
{
    class Program
    {
        static void Main(string[] args)
        {
            Core.Initialize();

            using (var libVlc = new LibVLC())
            using (var mediaPlayer = new MediaPlayer(libVlc))
            {
                var media = new Media(libVlc, "screen://", FromType.FromLocation);
                media.AddOption(":screen-fps=24");
                media.AddOption(":sout=#transcode{vcodec=h264,vb=0,scale=0,acodec=mp4a,ab=128,channels=2,samplerate=44100}:file{dst=testvlc.mp4}");
                media.AddOption(":sout-keep");

                mediaPlayer.Play(media);
                Thread.Sleep(10*1000);
                mediaPlayer.Stop();
            }
        }
    }
}

I realize the following suggestion doesn't answer your question, but the simplest method I have found to capture a rapidly-changing DirectX view, is to plug a video camera into the S-video port of the video card, and record the images as a movie. Then transfer the video from the camera back to an MPG, WMV, AVI etc. file on the computer.