Glossary

ABR. Adaptive bitrate. The controller that moves the encoder’s target bitrate to match what the connection can carry. On by default in smooth mode.

Admission. The check that decides whether a GPU can take a new session. Needs a free encode slot and enough free GPU memory.

Agent. See node agent.

App. A catalog entry a user can launch: content, a container specification and a launch command. Classified as a game, a desktop or a launcher.

AV1. A modern video codec. Saves 40 to 50 percent of H.264’s bitrate at equivalent quality, and Chrome can decode it everywhere thanks to a software fallback.

Constrained baseline. The H.264 profile browser sessions are clamped to, because Chrome’s WebRTC receiver cannot decode High profile from any encoder.

Control plane. The Go service holding accounts, the API, signaling and the scheduler. Backed by Postgres. Holds no per-host GPU state.

Device. A browser Quasar has seen a user log in from, along with the decode capabilities it measured. Used to avoid sending a codec the client cannot play.

Diagnostic bundle. A bounded window of a session’s metrics, events, clock alignment and an automated verdict. The thing to attach to a bug report.

DMABuf. The Linux mechanism that lets the compositor hand a frame to the VA-API encoder without copying it through system memory.

Encode slot. A unit of concurrent encoding capacity on a GPU. The real reservation in admission control.

Entitlement. The grant that decides whether an app appears in a user’s library. Granted to everyone or to named users.

Enrollment token. The shared secret a node agent presents on first contact. After a successful enrollment the agent uses its own stored node secret instead.

FEC. Forward error correction. Adds redundancy so lost packets can be reconstructed. Off by default and not recommended for browser clients.

GOP. Group of pictures. The interval between keyframes. Defaults to 60 frames.

H.264. The baseline video codec. Decodes everywhere. Every quality tier ends in an H.264 rung.

HEVC. Also called H.265. Saves 30 to 40 percent over H.264, but Chrome only decodes it with operating system hardware support, so effectively macOS and Windows only. The catalog calls it hevc and the wire calls it h265.

Home root. The directory on a host where managed home directories live. Must be the same path on every host, and genuinely shared storage if saves are to follow users between machines.

Host. A machine running the node agent. Owns GPUs and runs sessions.

ICE. The WebRTC mechanism for discovering a network path between two peers. A session stuck at “checking” means ICE found no working path.

Intra refresh. Replacing periodic keyframes with a rolling wave of intra-coded blocks. Vulkan encoder only, and needs a patched image.

Launch profile. An ordered list of stream profiles, best first. This is what a user picks, and what “1080p60” means in the interface.

Library provider. A source of games that can be discovered automatically. Steam is the only one that exists today.

Managed home. A user’s persistent directory for one app. Single writer, which is why only one session per user per app can run at a time.

Node agent. The Rust program on every GPU host. Owns the GPUs, runs the compositor and encoder, launches app containers.

NVENC. NVIDIA’s hardware encoder.

Placement. Choosing which host runs a session. Governed by QUASAR_PLACEMENT_POLICY.

Playout buffer. The client-side jitter buffer. Adapts to how evenly frames arrive. Uneven arrival forces a bigger buffer, and the buffer is latency.

Presentation interval variation. The standard deviation of the gap between displayed frames. The number that matches perceived stutter. Below 12 ms is healthy, above 18 ms is visible.

Render node. The DRM device the compositor and encoder use, under /dev/dri. Prefer a /dev/dri/by-path/ name, because the numbered names can move between reboots.

Rung. One stream profile inside a launch profile.

Runtime preset. A reusable container specification several apps can share.

Session. One user, one app, one host, one connection.

Signaling. The exchange over /v1/signal that lets a browser and a node agent find each other before they connect directly.

STUN and TURN. Standard WebRTC mechanisms for NAT traversal and relaying. A normal Quasar install uses neither: media takes a direct route between the browser and the GPU host, which means a LAN or a VPN.

Stream profile. One concrete encode rung: codec, resolution, frame rate, bitrate and eligibility thresholds. Users never see these.

VA-API. The video acceleration interface used for AMD and Intel encoding.

Vulkan encoder. The Vulkan Video encode path. Auto-detection selects it by default on AMD and NVIDIA; Quasar’s universal agent image carries its patched H.264, HEVC, and AV1 elements.

Wayland compositor. The gst-wayland-display element that gives a game something to render into and produces the frames that get encoded.

WebRTC. The browser technology carrying video, audio and input between the client and the GPU host.

Zero copy. Moving a frame from the compositor to the encoder without a trip through system memory. How the VA and NVENC paths are built.