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Omniform is a Tauri v2 desktop application. The Rust backend handles all process management, file I/O, archive extraction, and network downloads; the React frontend renders the UI and communicates with the backend exclusively through Tauri’s IPC bridge — there is no HTTP server, no WebSocket, and no shared memory between the two layers. Every action the user takes in the UI (adding a URL, picking a folder, cancelling a download) is translated into either a Tauri command call or a state update driven by an incoming Tauri event.

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High-level overview

Rust backend

Located in src-tauri/src/. Three modules:
  • lib.rs — app entry point. Registers all five Tauri commands, initialises the four plugins (shell, dialog, fs, clipboard-manager), creates the DownloadRegistry shared state, and ensures the binary directory exists on startup.
  • dependencies.rs — manages the automatic download and installation of yt-dlp and ffmpeg. Checks whether the binaries are present, fetches them from their respective sources if not, extracts archives in-memory, sets executable permissions on Unix, and emits deps://status events throughout.
  • downloads.rs — spawns yt-dlp as a child process for each download. Streams stdout line by line to parse progress output, emits download://progress events in real time, emits download://info after a pre-flight --dump-json call, and emits download://done or download://error on completion.

React frontend

Located in src/. Three layers:
  • App.tsx — root shell. Manages the output directory state, calls get_default_output_dir on mount, triggers ensure_dependencies if either tool is missing, and renders the three main UI sections.
  • useDownloadQueue hook — the central state manager. Invokes all Tauri commands and subscribes to all Tauri events. Owns the items array (the queue) and the deps status object. All other components receive state and callbacks from this hook.
  • Components — UrlForm collects the URL, format, and quality from the user; QueueItem renders a single download row with its progress bar, title, and action buttons; DependencyBanner shows yt-dlp/ffmpeg setup status and a Retry button if setup failed.

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IPC flow

The following trace shows the complete lifecycle of a single download, from the user clicking the Add button to the file appearing on disk: 
User submits URL in UrlForm
  → useDownloadQueue.addDownload(url, format, quality, outputDir)
      → makeId() generates a unique download ID
      → setItems() adds a new DownloadItem with status "queued"
      → invoke("start_download", { id, url, format, quality, outputDir })

Rust: lib.rs → downloads::start_download()
  → emits "download://progress" { status: "fetching-info" }
  → runs yt-dlp --dump-json to fetch title/thumbnail
  → emits "download://info" { id, title, thumbnail }
  → spawns yt-dlp child process for the real download
  → stores child in DownloadRegistry (keyed by id)
  → streams stdout, parses OMNIFORM_PROGRESS lines
  → emits "download://progress" { id, progress, speed, eta, status }
      (status transitions: "fetching-info" → "downloading" → "converting" → "done")
  → on success: emits progress { status: "done", progress: 100 }, then "download://done" { id, outputPath }
  → on non-zero exit with stderr: emits "download://error" { id, message }
  → on non-zero exit with empty stderr (cancelled): no error event emitted

Frontend: useDownloadQueue event listeners
  → listen("download://info")     → setItems() updates title and thumbnail
  → listen("download://progress") → setItems() updates progress, speed, eta, status
  → listen("download://done")     → setItems() sets status "done", progress 100
  → listen("download://error")    → setItems() sets status "error", errorMessage
  → React re-renders QueueItem with latest state

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Tauri commands

All five commands are registered in lib.rs via tauri::generate_handler! and are callable from the frontend with invoke().

check_dependencies

Returns a DependencyStatus object ({ ytDlpReady, ffmpegReady, downloading, message }) reflecting whether the yt-dlp and ffmpeg binaries currently exist on disk. This is a synchronous check — no network call is made. Called once on mount by useDownloadQueue.

ensure_dependencies

Downloads any missing binaries. Emits deps://status events during the process so the frontend can show progress. If both binaries are already present, it emits a single status event and returns immediately. This is the async command triggered by DependencyBanner and by App.tsx on startup.

get_default_output_dir

Returns the system Downloads folder path (falling back to the home directory) as a string. Used by App.tsx to pre-populate the output directory on first launch.

start_download

Accepts { id, url, format, quality, outputDir }. Runs a pre-flight yt-dlp --dump-json call, then spawns the full download process. Registers the child process in the DownloadRegistry so it can be cancelled. Emits the full sequence of download:// events until the process exits.

cancel_download

Accepts { id }. Looks up the child process in the DownloadRegistry by ID, calls kill() on it, and removes it from the registry. Once the command resolves, the frontend sets the item’s status to "cancelled".

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Event system

The Rust backend emits Tauri events that the frontend listens to via listen(). All event payloads include the download id so the frontend can match events to the correct queue item. Full payload type definitions are covered in the Events reference.
EventEmitted byPayload summary
download://infodownloads.rs{ id, title, thumbnail } — video title and thumbnail URL, fetched before the download starts
download://progressdownloads.rs{ id, progress, speed, eta, status } — numeric percent, speed string, ETA string, and a DownloadStatus string
download://donedownloads.rs{ id, outputPath } — the output directory path when the download and any conversion are complete
download://errordownloads.rs{ id, message } — the stderr output from yt-dlp when the process exits with a non-zero status
deps://statusdependencies.rs{ ytDlpReady, ffmpegReady, downloading, message } — emitted at each stage of the yt-dlp/ffmpeg setup flow

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Tauri plugin permissions

Permissions are declared in src-tauri/capabilities/default.json and apply to the main window. The app requests the minimum set of capabilities needed for its features:
PermissionWhy it is needed
core:defaultBase Tauri core permissions required by all apps
dialog:allow-openPowers the “Output folder” picker button — opens the native OS directory chooser
fs:allow-read-fileAllows the frontend to read files via the fs plugin if needed
fs:allow-write-fileAllows the frontend to write files via the fs plugin if needed
fs:scope-download-recursiveGrants the fs plugin access to the system Downloads directory tree
fs:scope-home-recursiveGrants the fs plugin access to the user’s home directory tree
shell:allow-openAllows QueueItem to open the output folder in the native file manager when a download finishes
clipboard-manager:allow-read-textAllows the app to read the clipboard so it can auto-populate the URL field when the user copies a link

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Download ID system

Each download is identified by a unique string ID generated entirely in the frontend before the start_download command is called: 
function makeId(): string {
  return `${Date.now()}-${Math.random().toString(36).slice(2, 9)}`;
}
The ID is passed as a parameter to start_download and is echoed back verbatim in the payload of every download:// event. This allows the useDownloadQueue hook to map incoming events to the correct item in the items array without any additional coordination — the Rust backend treats the ID as an opaque string and never generates or modifies it. The DownloadRegistry in downloads.rs uses this same ID as the key in its HashMap<String, Arc<Mutex<Child>>>, which is how cancel_download finds the right child process to kill.

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