[FFmpeg-trac] #11599(ffmpeg:new): `gdigrab` Screen Capture Causes Cursor Flickering and Focus Loss on Windows (Multi-Monitor)

[FFmpeg]

#11599: `gdigrab` Screen Capture Causes Cursor Flickering and Focus Loss on Windows
(Multi-Monitor)
--------------------------------+--------------------------------------
             Reporter:  Evgene  |                     Type:  defect
               Status:  new     |                 Priority:  critical
            Component:  ffmpeg  |                  Version:  git-master
             Keywords:          |               Blocked By:
             Blocking:          |  Reproduced by developer:  1
Analyzed by developer:  1       |
--------------------------------+--------------------------------------
 **Environment**
 - **OS**: Windows 11 Enterprise LTSC (Build 22000)
 - **FFmpeg Version**: Custom build `N-119502-g12b853530a-20250515`
 (`libavdevice 62.0.100`)
 - **Hardware**: Multi-monitor setup, high-resolution displays
 - **Reproducible**: Yes, with provided command

 ---

 ### **Steps to Reproduce**
 0. **Version**
 ```
 > ffmpeg -version
 ffmpeg version N-119502-g12b853530a-20250515 Copyright (c) 2000-2025 the
 FFmpeg developers
 built with gcc 14.2.0 (crosstool-NG 1.27.0.18_7458341)
 configuration: --prefix=/ffbuild/prefix --pkg-config-flags=--static --pkg-
 config=pkg-config --cross-prefix=x86_64-w64-mingw32- --arch=x86_64
 --target-os=mingw32 --enable-gpl --enable-version3 --disable-debug
 --enable-shared --disable-static --disable-w32threads --enable-pthreads
 --enable-iconv --enable-zlib --enable-libfribidi --enable-gmp --enable-
 libxml2 --enable-lzma --enable-fontconfig --enable-libharfbuzz --enable-
 libfreetype --enable-libvorbis --enable-opencl --disable-libpulse
 --enable-libvmaf --disable-libxcb --disable-xlib --enable-amf --enable-
 libaom --enable-libaribb24 --enable-avisynth --enable-chromaprint
 --enable-libdav1d --enable-libdavs2 --enable-libdvdread --enable-libdvdnav
 --disable-libfdk-aac --enable-ffnvcodec --enable-cuda-llvm --enable-frei0r
 --enable-libgme --enable-libkvazaar --enable-libaribcaption --enable-
 libass --enable-libbluray --enable-libjxl --enable-libmp3lame --enable-
 libopus --enable-librist --enable-libssh --enable-libtheora --enable-
 libvpx --enable-libwebp --enable-libzmq --enable-lv2 --enable-libvpl
 --enable-openal --enable-liboapv --enable-libopencore-amrnb --enable-
 libopencore-amrwb --enable-libopenh264 --enable-libopenjpeg --enable-
 libopenmpt --enable-librav1e --enable-librubberband --enable-schannel
 --enable-sdl2 --enable-libsnappy --enable-libsoxr --enable-libsrt
 --enable-libsvtav1 --enable-libtwolame --enable-libuavs3d --disable-libdrm
 --enable-vaapi --enable-libvidstab --enable-vulkan --enable-libshaderc
 --enable-libplacebo --enable-libvvenc --enable-libx264 --enable-libx265
 --enable-libxavs2 --enable-libxvid --enable-libzimg --enable-libzvbi
 --extra-cflags=-DLIBTWOLAME_STATIC --extra-cxxflags= --extra-libs=-lgomp
 --extra-ldflags=-pthread --extra-ldexeflags= --cc=x86_64-w64-mingw32-gcc
 --cxx=x86_64-w64-mingw32-g++ --ar=x86_64-w64-mingw32-gcc-ar
 --ranlib=x86_64-w64-mingw32-gcc-ranlib --nm=x86_64-w64-mingw32-gcc-nm
 --extra-version=20250515
 libavutil      60.  2.100 / 60.  2.100
 libavcodec     62.  3.101 / 62.  3.101
 libavformat    62.  0.102 / 62.  0.102
 libavdevice    62.  0.100 / 62.  0.100
 libavfilter    11.  0.100 / 11.  0.100
 libswscale      9.  0.100 /  9.  0.100
 libswresample   6.  0.100 /  6.  0.100

 Exiting with exit code 0
 ```

 ```
 > systeminfo | findstr /B /C:"OS Name" /B /C:"OS Version"
 OS Name:                   Microsoft Windows 11 Enterprise LTSC
 OS Version:                10.0.22000 N/A Build 22000
 ```



 1. **Command**:
 ```shell
 ffmpeg \
   -loglevel level+info \
   -y \
   -framerate 10 \
   -threads 4 \
   -fflags nobuffer \
   -avioflags direct \
   -probesize 32 \
   -analyzeduration 0 \
   -f gdigrab \
   -i desktop \
   -map 0:v \
   -f rawvideo \
   -pix_fmt rgb24 \\.\pipe\ffmpeg_video
 ```

 2. **Actions During Capture**:
    - Move cursor rapidly across secondary monitor.
    - Attempt to select text or drag UI elements (e.g., in a text editor).

 3. **Result**:
    - Visible cursor flickering.
    - Intermittent loss of focus during interactions (e.g., text selection
 resets).

 ---

 ### **Root Cause**
 The `gdigrab` device in FFmpeg’s `avdevice` library forcibly repositions
 the cursor during frame capture[^1]. On multi-monitor/high-DPI systems,
 this introduces a race condition:
 - FFmpeg moves the cursor to capture its position/sprite.
 - Windows UI thread fails to restore the cursor quickly enough, causing
 flickering and focus instability.

 ---

 ### **Workaround (Verified)**
 **Patch `avdevice-62.dll`**:
    Modify the library to **skip cursor repositioning** during capture.
 Tools like x64dbg or Ghidra can be used to:
    - Locate the cursor position update logic in `gdigrab`’s capture loop.
    - NOP (disable) instructions that call `SetCursorPos()` or equivalent
 Win32 APIs.

 ---

 ### **Proposed Upstream Fix**
 1. **FFmpeg Code Change**:
    In `libavdevice/gdigrab.c`, modify the cursor handling logic to:
    ```c
    // Replace physical cursor movement with position caching
    static void capture_cursor(...) {
        // GetCursorPos(&cursor_pos);  // <-- Remove this
        // SetCursorPos(cursor_pos.x, cursor_pos.y);  // <-- Remove this
        // Draw cursor sprite on frame using cached position
    }
    ```

 2. **Alternative**: Modify `-draw_mouse 0` flag to avoid mouse
 interaction.

 ---

 ### **References**
 [^1]: [FFmpeg gdigrab Cursor Flicker Discussion
 (2020)](https://stackoverflow.com/questions/34023630)
 [^2]: [Previous conversation](https://ffmpeg.org/pipermail/ffmpeg-
 devel/2019-December/255101.html)
-- 
Ticket URL: <https://trac.ffmpeg.org/ticket/11599>
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