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trajectory-recorder-cpp

C++20 scaffold for recording synchronized gameplay trajectories as video frames plus input state streams for downstream reinforcement-learning dataset conversion.

Software stack

  • Conan for package management
  • Meson and Ninja for builds
  • GStreamer for capture
  • SDL3 for input
  • Protobuf for action serialization
  • OpenCV for offline replay
  • FTXUI for TUI
  • yaml-cpp for mapping config IO

Layout

  • include/ public headers
  • src/ implementation and CLI entrypoints
  • protos/ protobuf schema and Meson generation rules
  • tests/ no-dependency unit tests for binary framing helpers
  • specs/ product and implementation specs
  • scripts/build.ps1 helper to run Conan, Meson, and tests

Dependency installation

Windows

Build

Prerequisites on Windows:

  • Conan available on PATH
  • Meson and Ninja available on PATH
  • A working C++20 compiler toolchain
  • GStreamer development/runtime packages installed
  • ViGEmBus installed if you want to record with gamepad forwarding enabled or run the virtual gamepad bridge sample

The build helper links GStreamer directly from an existing Windows installation root instead of relying on pkg-config-derived linker flags for the GStreamer libraries.

If GStreamer is installed at C:\Program Files\gstreamer\1.0\msvc_x86_64, pass that root explicitly:

./scripts/build.ps1 -GStreamerRoot 'C:\Program Files\gstreamer\1.0\msvc_x86_64'

The helper exports:

  • GSTREAMER_1_0_ROOT_X86_64
  • PATH += <GStreamerRoot>\bin
  • PKG_CONFIG_PATH += <GStreamerRoot>\lib\pkgconfig

If GStreamer is installed somewhere else, pass the root explicitly:

./scripts/build.ps1 -GStreamerRoot D:\path\to\gstreamer\1.0\msvc_x86_64

Open a Developer Powershell for VS 20XX (shell with compiler toolchain installed)

Then run:

./scripts/build.ps1

The helper rebuilds Conan-managed dependencies to match the active MSVC runtime, build type, and C++20 setting when needed, and it uses the Conan-provided protoc.

Fast Rebuild

If builddir already exists from a successful ./scripts/build.ps1 run, you can do an incremental rebuild without rerunning Conan or Meson reconfiguration.

Open a Developer PowerShell for VS and run:

meson compile -C builddir

If you also want to rerun the test suite after the incremental rebuild:

meson test -C builddir --print-errorlogs

Use ./scripts/build.ps1 again when dependencies, Conan settings, GStreamer location, or Meson configuration have changed.

Clean Build Files

To remove the default build output directory created by the helper script:

Remove-Item -Recurse -Force builddir

To remove Conan-generated temporary and build files created by conan install, delete the generated files from the build directory:

Remove-Item -Recurse -Force builddir

If you want to clear Conan's local cache artifacts as well, use:

conan remove "*" --confirm

This removes all cached Conan packages and metadata from your local Conan cache, so the next build will resolve and rebuild dependencies from scratch.

Usage

After building, run the executables:

  • record_session [output_dir] [session_name]
  • validate_recording <session_dir|sessions_root>
  • map_actions <game-actions.yaml> [action-mapping.yaml] [--profile-name <name>] [--resume-from <existing.yaml>] [--max-combo-buttons <n>]
  • virtual_gamepad_bridge
  • convert_dataset <capture.mp4> <sync.csv> <actions.bin>

Record Game Sesion

record_session now supports pre-recording capture selection:

  • --monitor <id> selects a monitor by the one-based ID shown in the selector
  • --window <title> selects a titled window by case-insensitive substring match
  • --verbose prints each recorded input snapshot to stdout as it is written
  • if neither flag is provided, an FTXUI-based selector opens before recording starts

Examples:

.\builddir\record_session.exe .\data test_session --monitor 1
.\builddir\record_session.exe .\data test_session --window "Notepad"
.\builddir\record_session.exe .\data test_session --monitor 1 --verbose

When running record_session.exe from PowerShell on Windows, use a Developer PowerShell and make sure the GStreamer runtime bin directory is on PATH. If Windows cannot load the GStreamer DLLs, the process can exit before main() starts and you will see no program output. The recorder also pumps SDL input events on the main thread. If that polling is moved to a worker thread, SDL 3 can raise assertion popups on Windows. record_session now also creates a virtual Xbox 360 controller through ViGEmBus and forwards the tracked physical gamepad into it while it logs actions.bin. If a game should see only the forwarded virtual controller, hide the physical device separately with HidHide or equivalent tooling before you start recording.

Example:

$env:GSTREAMER_1_0_ROOT_X86_64 = 'C:\Program Files\gstreamer\1.0\msvc_x86_64'
$env:PATH = "$env:GSTREAMER_1_0_ROOT_X86_64\bin;$env:PATH"

.\builddir\record_session.exe .\data test_session

If you want to rebuild and then run in the same shell:

./scripts/build.ps1
$env:PATH = "C:\Program Files\gstreamer\1.0\msvc_x86_64\bin;$env:PATH"
.\builddir\record_session.exe .\data test_session

Validate Recording

validate_recording validates one recorded session or scans a directory containing multiple session folders.

Examples:

.\builddir\validate_recording.exe .\data\test_session
.\builddir\validate_recording.exe .\data --json
.\builddir\validate_recording.exe .\data --csv
.\builddir\validate_recording.exe .\data\test_session --mode step

The validator currently:

  • checks for required files: capture.mp4, sync.csv, actions.bin
  • parses sync.csv and actions.bin
  • reports timing, dead-period, idle-gap, and input-frequency statistics
  • supports summary, JSON, CSV, and text-based step-through modes

Virtual Gamepad Bridge

virtual_gamepad_bridge is a Windows-only integration sample for ViGEmClient. Its goal is to test whether the gamepad forwarding used while recording a game session works correctly. It opens the first SDL gamepad it can see, creates a virtual Xbox 360 controller through ViGEmBus, and forwards live input changes into that virtual device.

Requirements:

  • ViGEmBus must be installed before running the sample
  • if you want a game to see only the virtual controller, hide the physical controller separately with HidHide or equivalent tooling

Run it from a Developer PowerShell after building:

.\builddir\virtual_gamepad_bridge.exe
.\builddir\virtual_gamepad_bridge.exe --max-forward-log-lines-per-second 60

The sample prints basic lifecycle status plus rate-limited forwarded button logs in the form <physical_gamepad_id>.<button> -> <virtual_gamepad_id>.<button>. The default cap is 30 printed lines per second, and --max-forward-log-lines-per-second <n> lets you raise or lower that limit. It exits on Ctrl+C.

Gamepad Mapping

map_actions builds a per-user mapping between raw gamepad inputs and in-game action IDs defined in a YAML game definition file.

Examples:

.\builddir\map_actions.exe .\configs\game-actions.yaml
.\builddir\map_actions.exe .\configs\game-actions.yaml .\profiles\action-mapping.yaml --profile-name "steam-deck"
.\builddir\map_actions.exe .\configs\game-actions.yaml .\profiles\action-mapping.yaml --resume-from .\profiles\action-mapping.yaml
.\builddir\map_actions.exe .\configs\game-actions.yaml .\profiles\action-mapping.yaml --max-combo-buttons 3
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