A paid course platform where lessons alternated between video and interactive programs. It shipped three course series. Its flagship machine-learning course took the site down on launch day.
Capsule artwork for the flagship course, The Birth of an AI.
Role
Core business logic and API design; JavaScript-to-TypeScript migration; performance and memory; interaction nodes and motion design; internal animation tooling
Team
Dehydration Culture, interactive video team. The platform was a team build; see My role.
Timeline
Platform launched December 2019. Joined 2020, left 2022. Future development halted December 2021.
Outcome
3 course series shipped. ¥49 flagship course with a launch-day outage. Player framework later open-sourced as Recative.
01 · The product
Playground launched in December 2019 as a paid platform for interactive video courses. In each lesson, video segments and interactive programs alternate: the video explains an idea, and the program lets the learner operate on it. The courses were made for a Chinese-speaking audience, so the screenshots on this page show the original interface. I joined the team in 2020 and worked on the platform until 2022.
Three course series shipped on the platform:
Released December 2020
Twelve chapters, from recognizing handwritten digits to training a neural network. Two years in development. Priced at ¥49 with a one-yuan trial chapter. Later released on Steam.
Flagship course · 12 chapters
Cryptography course
Cryptography taught through interactive cipher machines, from classical ciphers to modern encryption. Later released on Steam.
Steam release
Early access
Statistical inference taught as an interactive story. Released as an early-access episode. As development wound down, a scaled-down complete version was later given free to existing paying users. The cover states the course’s stance: do not trust intuition, and do not stop thinking.
Early access · Episode 102 · The thinking
The audience was people who want to learn through video without staying passive: they want to participate, to practice, and to progress along a smooth learning curve.
Interactivity had two jobs. Tasks and puzzles inside the lesson deepen comprehension. Conversational UI and real-time data collection show how the learner is progressing while the lesson runs.
Content-production tools can be mapped on two axes, complexity and user engagement. Slide tools sit low on both, game engines sit high on both. Interactive video sits in the empty middle: higher engagement than slides, lower production complexity than game-engine content.
03 · The craft
Each of these three decisions began as a flaw that users could see. The full technical history is on the blog, from 2022 and in Chinese.
Early lessons switched from video to interaction through a visible modal window. The rebuilt player uses the video’s last frame as the first scene of the interaction, with the same audio continuing underneath. The cut is hard to notice even when you know where it is. My boss did not notice it the first time he watched.
Preloading every video at once crashed AMD graphics drivers and left users with a black screen. The fix was a rework of the loading lifecycle plus a resource manager with priority tags. Where waiting could not be removed, it was filled: the player detects the GPU, then plays a three-part WebGL animation while assets load. Later changelogs describe the result in product terms: users saw a loading indicator less often during playback.
Mobile support came late, and the first mobile builds ran hot. A colleague joked that the phone ran hotter than Genshin Impact. The fix was a frame-rate request system behind one interface: 60 frames per second while something moves, 15 when idle, back to 60 the moment the user interacts. The overheating reports stopped.
04 · The interactions
From The Birth of an AI. The team worked from static visual designs; turning them into working interactive programs, and designing the motion inside them, was engineer work. Every course was a team production. Screenshots show the shipped Mandarin interface.
05 · Reception
2020-12-17
The Birth of an AI launches. Launch-day traffic takes the site down; the team tells users that engineers are fixing it around the clock.
¥49 / ¥1
Full course price, with a one-yuan trial chapter. A retail partnership with Digital Lychee followed in March 2021.
¥500,000+
Revenue by the end of launch month.
2 years
Development time of the flagship course.
Coverage included The Paper, Tencent News, 36Kr and Appinn. A sixteen-minute excerpt circulated on Bilibili, and a public evaluation thread on Zhihu collected both praise and detailed criticism. Both completed courses were later released on Steam. Official update posts thanked beta testers by name, and tester feedback shaped each content update.
06 · User response
The course was reviewed publicly, including a long evaluation thread on Zhihu. The feedback reached the team and shaped later updates.
07 · My role
The platform was a team build: I set the architecture, built the business logic that crossed teams, and did some interface and product design; most of the development was done by colleagues. The night the largest architecture change shipped, the main user flow had zero bugs. It was the first time in my two years there.