Preferences

The Preferences window contains application-level settings (not per-project settings).

Opening Preferences

Enable hardware acceleration toggles the saved preference value and applies immediately to source preview playback.
The setting is persisted across launches and available via MCP automation.
Implementation: When enabled, the GStreamer pipeline builds the glsinkbin path for higher performance; when disabled, it uses the software-based gtk4paintablesink path.
Does not change export behavior.

Program monitor playback priority controls how playback trades off smoothness vs precision:
- Smooth (default): favors continuity and lower stutter during active playback.
- Balanced: middle ground.
- Accurate: favors precise seeks/frame placement.
The setting is persisted across launches.
MCP automation:
- get_preferences returns playback_priority.
- set_playback_priority updates the mode.

Enable occlusion-based decode skip: when enabled, clips fully hidden behind an opaque full-frame overlay (e.g. a B-roll clip covering the main track) skip video decoding and effects processing. This significantly reduces CPU/GPU load during multi-track playback.
Enable continuous decoders: reuses existing decoder slots at boundary crossings when adjacent clips share the same source file. This eliminates the teardown/rebuild overhead and can reduce boundary latency by up to 75%.
Real-time preview toggle: allows switching between prioritized real-time playback (dropping frames if needed) and frame-accurate playback (slowing down if needed to show every frame).
These settings are persistent and recommended for complex projects with many overlapping tracks.

Proxy preview mode generates lightweight proxy files for smoother preview playback with large/high-bitrate media:
- Off (default): uses original source media.
- Half Res: generates half-resolution H.264 proxies.
- Quarter Res: generates quarter-resolution H.264 proxies.
When Proxy mode is Off, UltimateSlice now auto-enables proxies during heavy live-preview regions (3+ overlapping video tracks) to keep playback responsive, then returns to original media when overlap drops below that threshold.
Auto-enabled proxy scale follows current preview pressure: Half-res by default, Quarter-res when preview quality is reduced to Quarter.
Proxy files are transcoded in the background via ffmpeg and stored in .ultimateslice_proxies/ next to the source files.
A yellow progress bar appears at the bottom of the window during proxy generation.
Changing the proxy size (e.g. from Half Res to Quarter Res) automatically invalidates existing proxies and re-generates them at the new resolution.
LUT-baked proxies: when a LUT is assigned to a clip via the Inspector, a new proxy is generated for that clip with the LUT baked in, so the preview reflects the color grade. Removing the LUT regenerates a plain (ungraded) proxy.
Export always uses original full-resolution media regardless of proxy mode.
The setting is persisted across launches.
MCP automation:
- get_preferences returns proxy_mode.
- set_proxy_mode updates the mode and re-generates proxies as needed.

Preview quality scales down the compositor output resolution for preview playback:
- Auto: adapts quality to the current Program Monitor canvas size.
- Full (default): renders at project resolution (e.g. 1920×1080).
- Half: halves both dimensions (e.g. 960×540) — 4× fewer pixels, significantly less memory and CPU.
- Quarter: quarters both dimensions (e.g. 480×270) — 16× fewer pixels, best for low-memory devices.
Reduced preview quality keeps the same framing as Full quality: the full composed frame is scaled to fit the monitor (no top-left cropping).
Takes effect immediately — no restart required.
Export always uses full project resolution regardless of this setting.
Combine with Proxy preview mode for maximum performance on constrained hardware: Quarter-res proxies + Quarter preview quality minimizes both decode and compositing cost.
The setting is persisted across launches.
MCP automation:
- get_preferences returns preview_quality.
- set_preview_quality updates the quality level (auto, full, half, quarter).

Show timeline preview controls video thumbnail rendering in the timeline:
- Enabled (default): show the regular thumbnail strip across each visible video clip.
- Disabled: only show start/end thumbnails for each visible video clip.
Show audio waveforms on video clips draws a color-coded waveform overlay on the lower portion of video clips in the timeline.
Use these options to balance visual feedback and thumbnail-generation workload on heavy media/projects.
The settings are persisted across launches.

GTK renderer controls which graphics backend GTK uses to draw the application window:
- Auto (default): let GTK decide (usually Vulkan on supported systems).
- Cairo (Software): CPU-based rendering — uses no GPU memory at all. Best for devices with limited GPU memory that see VK_ERROR_OUT_OF_DEVICE_MEMORY errors.
- OpenGL: moderate GPU memory usage — a good middle ground.
- Vulkan: explicit Vulkan rendering — highest quality, highest GPU memory usage.
Requires a restart to take effect (the renderer is selected before GTK initializes).
Export is unaffected — it always uses ffmpeg regardless of the renderer setting.
The setting is persisted across launches.
MCP automation:
- get_preferences returns gsk_renderer.
- set_gsk_renderer updates the mode (restart required to apply).

Enable MCP socket server allows AI agents to connect to this running instance via a Unix domain socket.
When enabled, UltimateSlice listens at $XDG_RUNTIME_DIR/ultimateslice-mcp.sock.
The toggle takes effect immediately — no restart required.
Only one agent can be connected at a time; additional connections are rejected.
Agents using the .mcp.json ultimate-slice-attach server entry connect via --mcp-attach, which bridges stdio to the socket.
The setting is persisted across launches.

get_preferences: returns current application preferences.
set_hardware_acceleration: toggles hardware acceleration.
set_playback_priority: sets Program Monitor playback priority (smooth, balanced, accurate).
set_source_playback_priority: sets Source Monitor playback priority.
set_proxy_mode: sets proxy preview mode (off, half_res, quarter_res).
set_preview_quality: sets compositor preview quality (auto, full, half, quarter).
set_gsk_renderer: sets GTK renderer backend (restart required).
set_realtime_preview: enables or disables real-time preview optimizations.