Fastest method of screen capturing on Windows

Question

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

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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

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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

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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

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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

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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

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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

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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

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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

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You can try the c   open source project WinRobot  git  a powerful screen capturer   CComPtr lt IWinRobotService gt  pService  hr   pService CoCreateInstance   uuidof ServiceHost        get active console session CComPtr lt IUnknown gt  pUnk  hr   pService- gt GetActiveConsoleSession  amp pUnk   CComQIPtr lt IWinRobotSession gt  pSession   pUnk      capture screen pUnk   0  hr   pSession- gt CreateScreenCapture 0 0 1280 800  amp pUnk       get screen image data with file mapping  CComQIPtr lt IScreenBufferStream gt  pBuffer   pUnk    Support     UAC Window Winlogon DirectShowOverlay

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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- gt GetRenderTarget 0   amp pRenderTarget         get the current adapter display mode       hr   pDirect3D- gt GetAdapterDisplayMode D3DADAPTER DEFAULT  amp d3ddisplaymode          create a destination surface     hr   Device- gt CreateOffscreenPlainSurface DisplayMde Width                           DisplayMde Height                           DisplayMde Format                           D3DPOOL SYSTEMMEM                            amp pDestTarget                           NULL        copy the render target to the destination surface     hr   Device- gt GetRenderTargetData pRenderTarget  pDestTarget        save its contents to a bitmap file     hr   D3DXSaveSurfaceToFile file                                D3DXIFF BMP                                pDestTarget                                NULL                                NULL          clean up     pRenderTarget- gt Release       pDestTarget- gt Release

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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

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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      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  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

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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

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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

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