HelloWorld: Enabling Socially Interactive Characters in Video World Models

Liangyang Ouyang^1,2, Ruicong Liu², Xuangeng Chu², Kaipeng Zhang², Yoichi Sato¹

¹The University of Tokyo    ²Alaya Lab

HelloWorld is a video world model that enables social interaction with in-world characters. With a single button press (F), users can prompt the on-screen character to respond toward the camera, e.g., turning to the viewer, waving, nodding, or speaking a short greeting, while maintaining high-quality scene and camera-trajectory reconstruction.

• Self-distillation training: the base video generation model is finetuned on data synthesized by itself, containing both social interactions and camera motion, so it learns camera-pose conditioning without degrading interaction quality.
• Training-free temporal control: at inference, a temporal cross-attention mask localizes the character's response to the F-press window.
• HelloWorldBench: a 400-sample benchmark with three social interaction metrics (ActAcc, TimeAcc, GazeDev) alongside three conventional metrics.

Paper

📄 HelloWorld.pdf

Demo Video

▶️ HelloWorld.mp4

Code & Benchmark

Coming soon.

Contact

For questions, please contact oyly@iis.u-tokyo.ac.jp or liangyang.ouyang@shanda.com.