OpenDrop VJ

A 4-deck Milkdrop VJ instrument built on libprojectM: GPU compositor, MIDI/OSC/Ableton Link control, NDI in/out, and a phone remote control, packaged as a native Rust/egui desktop app.

This is the native rewrite. The previous Electron/SvelteKit web app lives on the legacy-web branch.

Features

• 4 decks with crossfader, playlists, snapshots, and a preset browser backed by libprojectM
• Beat detection, per-slot LFO, and beat-triggered modulation
• Live Time/Q-var parameter injection into the running preset
• Compositor: blend modes, luma/color keying, text and sprite overlays, strobe
• Control surfaces: MIDI (learn-based mapping), OSC, a phone remote control served over WebSocket, and optional Ableton Link
• Output: NDI in/out, v4l2loopback, OBS WebSocket scene control, Twitch/Kick chat
• Cloud presets and shareable set links
• Local video clip playback and camera capture via ffmpeg

Screenshots

Building

cargo build --workspace

NDI SDK (build-time dependency)

Building this workspace, including just the io or app crate (app depends on io), needs the NDI SDK (headers + libs) present at build time, not only at runtime: grafton-ndi uses bindgen in its build.rs, which makes it a real build dependency rather than a runtime dlopen.

Two versioned files bridge this machine's Arch packaging: ndi-sdk-shim/ (symlinks under include/lib/x86_64-linux-gnu to the pacman ndi-sdk package's system locations) and .cargo/config.toml (points NDI_SDK_DIR at ndi-sdk-shim when the shell doesn't already export it). See the comment at the top of .cargo/config.toml for the full workaround.

On another machine or SDK layout (the standard NewTek installer, a different distro): either export your own NDI_SDK_DIR before building, or replace/remove ndi-sdk-shim/ and the [env] entry in .cargo/config.toml accordingly. The SDK itself is available from ndi.video.

This requirement (NDI SDK plus a libprojectm dev package) applies to every build machine, Windows included; see packaging/windows/README.md for the platform-specific setup there.

Known limitation: NDI discovery

NDI network discovery (enumerating NDI sources published on the local network in the UI) depends on an Avahi daemon running on the host. The distributed AppImage can't bundle a system daemon, so this limitation is accepted rather than worked around. The app runs normally without it; automatic NDI source discovery just won't be available, while direct access by URL or IP address still works.

Ableton Link (optional, GPL)

Ableton Link support (io::link / the Link panel) is disabled by default: it's neither compiled nor linked into the binary produced by a standard cargo build.

Reason: this support is built on rusty_link, a Rust binding to Ableton's official C++ Link library, distributed under GPL-2.0-or-later. Unlike LGPL, GPL has no permissive dynamic-linking clause, so linking rusty_link, static or dynamic, puts the whole resulting binary under GPL-2.0-or-later.

To enable it explicitly:

cargo build --features opendrop-app/link

(opendrop-app is the binary crate's package name, declared in app/Cargo.toml, not its directory name app/.)

A binary built with this feature must be treated as GPL-2.0-or-later as a whole, not under this project's default license. It must stay out of any binary packaged or distributed by default; the link feature is for local/optional builds that knowingly accept that license contamination.

ffmpeg (runtime dependency)

Two features shell out to ffmpeg, which must be on PATH at runtime (nothing links against it at build time):

• v4l2loopback output (io::v4l2loopback): the compositor writes its RGBA frames into a v4l2loopback device.
• Video panel (io::video_capture): local clip decoding and camera capture, in the other direction: ffmpeg writes raw RGBA frames to its stdout, and the app uploads them as a GL texture.

Without ffmpeg, both panels show an error and the rest of the app runs normally. Video clips themselves aren't bundled; see app/assets/video-loops/README.md.

Native file dialog (rfd)

The CloudPresets (ui::cloud_presets, Upload button) and Video (ui::video, "+ Video" button) panels use rfd for a native file picker. On Linux, rfd's default backend (features xdg-portal + async-std, not gtk3) goes through xdg-desktop-portal via D-Bus (ashpd), so no GTK3 library is needed at build or link time. At runtime, this backend does need an xdg-desktop-portal service (plus a portal implementation, e.g. xdg-desktop-portal-gtk/-kde/-hyprland) running in the session; without it, the Upload button silently fails to open a picker rather than failing the build.

Packaging

• Linux: AppImage, via packaging/appimage/build-appimage.sh.
• Windows: portable zip, via packaging/windows/build-portable.ps1. See packaging/windows/README.md for the vcpkg/projectM setup this depends on.

License

MIT, except the optional link feature above, which is GPL-2.0-or-later when enabled.