Timeliner is a C++ library that provides a timeline playback runtime designed to be dropped into game engines, 3D software, and other real-time applications. Think of it as the sequencing brain behind cinematics, cutscenes, procedural animations, or any system where "things happen at specific times along a track."

Timeline-based playback is one of those problems that seems trivial until you actually try to build it. You quickly run into gnarly edge cases:

• Scrubbing backward through events that had side effects when played forward
• Variable playback rates, pauses, and time dilation
• Nested timelines and sub-sequences with their own local time
• Deterministic behavior across frame rates for networked or replay scenarios
• Efficient event lookup when you have thousands of keyframes

Most game engines ship their own timeline systems (Unreal's Sequencer, Unity's Timeline, Godot's AnimationPlayer), but they're deeply coupled to the host engine. A standalone, engine-agnostic C++ library for timeline playback is genuinely useful — you can integrate it into custom engines, DCC tool plugins (Maya, Blender, Houdini), VFX pipelines, or even non-graphics applications like audio sequencers and simulation frameworks.

The zero-star status suggests this is very early, but the framing in the description is precise and mature — the author clearly understands the problem domain and the value of keeping the runtime decoupled from any specific rendering or gameplay system.

Who benefits: Custom engine developers, indie game studios building their own tooling, technical artists writing DCC plugins, and anyone building sequencing-heavy applications who doesn't want to reinvent playback state management from scratch. Also anyone learning how a robust playback runtime should be architected — a clean reference implementation is worth its weight in gold.