Loop Finder for foobar2000

foo_loop_finder is a beat-grid loop editor for foobar2000 v2 x64. It is designed for finding musical loops visually and, later, auditioning synchronized drum patterns over them.

Current scope

• Display-ready waveform peak/RMS reduction
• Manual BPM and rhythmic grid calculation
• Configurable grid offset and subdivisions
• Free or beat-division snapping with draggable IN/OUT points
• Editable 20-300 BPM and robust four-tap tempo entry
• Beat, subdivision and emphasized bar overlays
• Per-track grid and marker persistence
• Opt-in seek-based Loop transport, always disabled on startup and track changes
• Platform-independent core with unit tests
• Installable x64 foobar2000 component registration
• Default UI panel with current title, playback state and entire-track waveform
• Smooth playback cursor, click-to-seek, wheel zoom and drag navigation
• Cancellable background decoding and an eight-track in-memory waveform cache

The native component registers Loop Finder 0.1.0 and provides a Loop Finder Default UI element. The panel displays the current title, Playing/Paused/Stopped state, analysis status, waveform and playback cursor, plus the rhythmic editor. The visible Loop control now seeks from OUT to IN after a normal forward crossing. It uses ordinary foobar2000 seeks, so an audible boundary gap or click is expected until the later buffered M7 design.

Editor controls:

• Enter BPM from 20 through 300 (decimals such as 92.5 are supported).
• Press Tap or Ctrl+T four or more times for rolling-median tap tempo.
• Enter grid phase in milliseconds; negative finite offsets are supported.
• Select free placement, 1 beat, 1/2, 1/4, 1/8 or 1/16 beat snapping.
• Use Set IN / Set OUT at the playback cursor or drag marker lines.
• Inspect loop time, seconds, beats and meaningful whole-bar duration.
• Arm Loop (seek-based) to audition the selected region.
• Seek manually inside to re-arm, or outside to leave playback there until it is observed inside the loop again.

Waveform interactions:

• Click the waveform to seek when foobar2000 reports the track as seekable.
• Turn the mouse wheel over the waveform to zoom around the pointer, up to 64x.
• Drag horizontally to navigate a zoomed view.
• Drag an IN or OUT marker line to edit it; marker hits take priority over pan.
• Double-click to restore the whole-track overview.

The static waveform is rendered to one off-screen layer. The grid is composed into a separate cached presentation layer, while the two lightweight marker lines and playback cursor are drawn over that cache. Marker edits therefore do not rebuild the grid, waveform analysis or waveform bitmap. During ordinary playback, redraws occur only when the cursor crosses a display pixel and affect only its old and new strips. Analysis format waveform-v2 retains up to 262,144 bins so zoomed views do not have to enlarge low-resolution overview data.

When a pan rebuild is needed, the last completed layer remains visible until the replacement is ready and is then copied to the panel in one operation.

Analysis is intentionally limited to decoder-supported local tracks with a positive known duration. Remote, unsupported, zero-length and unknown-length sources show Analysis unavailable and do not affect playback. The waveform cache is memory-only and is cleared when the panel/component session ends. Editor metadata is stored separately through foobar2000's per-track index, keyed by path and subsong. It never writes audio tags or saves the active Loop flag; orphaned records expire after 26 weeks.

Windows build

The build requires Windows, Visual Studio Build Tools 2022 with the Desktop development with C++ workload, and the official foobar2000 SDK 2025-03-07. The Visual Studio IDE, WTL, and ATL are not required.

Extract the SDK contents into external\foobar2000-sdk so the layout is:

external\foobar2000-sdk\
├── foobar2000\
│   ├── SDK\
│   ├── shared\
│   └── foobar2000_component_client\
└── pfc\

From a regular PowerShell terminal in the repository root, run:

.\build.ps1 -Clean

To keep the SDK elsewhere, pass its extracted root:

.\build.ps1 -Clean -FoobarSdkPath "D:\path\to\SDK-2025-03-07"

The script discovers and initializes Build Tools, builds and tests the CMake core in the generator-specific build\vs2022-x64 directory, builds the native MSBuild project, and creates these installable outputs:

build\native\Release\foo_loop_finder.dll
build\foo_loop_finder.fb2k-component

Install the package using foobar2000 → File → Preferences → Components → Install, apply the change, and restart when prompted. The package is a ZIP-compatible archive with foo_loop_finder.dll at its root.

To show the panel, enable Default UI layout editing, add Loop Finder from the Playback Information group, and disable layout editing again.

See docs/BUILD_WINDOWS.md for requirements, troubleshooting, direct MSBuild usage, and all artifact paths.

SDK-independent core build

The platform-independent library and tests can still be built without the foobar2000 SDK:

cmake -S . -B build\core
cmake --build build\core
ctest --test-dir build\core --output-on-failure

Roadmap

1. Complete M5 transport and boundary-jitter acceptance in foobar2000
2. Add automatic BPM/beat detection in M6
3. Add buffered/crossfaded looping in M7
4. Add synchronized Boom bap, Funk, Rock and Jazz drum DSP