--- title: Replit — We Built a Video Rendering Engine by Lying to... description: Replit built a video rendering engine that captures arbitrary web pages as deterministic MP4 videos by virtualizing browser time. The system injects a... canonical: https://daily.dev/posts/replit-we-built-a-video-rendering-engine-by-lying-to-the-browser-about-what-time-it-is-8jyaegwtp twitter:card: summary_large_image twitter:site: @dailydotdev og:type: website og:site_name: daily.dev og:title: Replit — We Built a Video Rendering Engine by Lying to the Browser About What Time It Is | daily.dev og:description: Replit built a video rendering engine that captures arbitrary web pages as deterministic MP4 videos by virtualizing browser time. The system injects a... og:url: https://daily.dev/posts/replit-we-built-a-video-rendering-engine-by-lying-to-the-browser-about-what-time-it-is-8jyaegwtp og:image: https://api.daily.dev/og/posts/8JyAeGwTp.png og:image:alt: Replit — We Built a Video Rendering Engine by Lying to the Browser About What Time It Is og:image:width: 1200 og:image:height: 630 og:locale: en --- > ## Documentation Index > Fetch the complete documentation index at: https://daily.dev/llms.txt > Use this file to discover all available pages before exploring further. # Replit — We Built a Video Rendering Engine by Lying to the Browser About What Time It Is **[Hacker News](https://daily.dev/sources/hn)** · 9 min read · 0 upvotes · 0 comments ## Summary Replit built a video rendering engine that captures arbitrary web pages as deterministic MP4 videos by virtualizing browser time. The system injects a ~1,200-line JavaScript shim that replaces setTimeout, setInterval, requestAnimationFrame, Date, and performance.now() with a fake clock that advances only when the renderer says so. Additional challenges solved include: a compositor warmup loop to prevent Chrome's internal buffers from going stale, a five-layer video element pipeline (MutationObserver → FFmpeg transcoding → mp4box.js demuxing → WebCodecs decoding → canvas rendering), and audio capture via monkey-patching Web Audio API entry points to intercept playback intent rather than recording speaker output. The system disables OffscreenCanvas for determinism, includes SSRF protection for untrusted URLs, and runs single-flight to avoid resource contention. The approach is inspired by the open-source WebVideoCreator project but was rewritten in TypeScript with modern Puppeteer and adapted for Replit's cloud infrastructure. An open-source release is planned. ## Full article daily.dev links to this article rather than hosting it. Read it at the original source: ## Similar posts on daily.dev - [How we built a free video editor that never uploads your files](https://daily.dev/posts/how-we-built-a-free-video-editor-that-never-uploads-your-files-iog9cmrlm) · Medium · 17 upvotes · 1 comments --- Tags: [#webdev](https://daily.dev/tags/webdev), [#backend](https://daily.dev/tags/backend), [#crawling](https://daily.dev/tags/crawling) [View this post on daily.dev](https://daily.dev/posts/replit-we-built-a-video-rendering-engine-by-lying-to-the-browser-about-what-time-it-is-8jyaegwtp) ```json {"@context":"https://schema.org","@graph":[{"@type":"Organization","@id":"https://daily.dev/#organization","name":"daily.dev","url":"https://daily.dev","logo":{"@type":"ImageObject","url":"https://daily.dev/apple-touch-icon.png","width":180,"height":180},"sameAs":["https://twitter.com/dailydotdev","https://github.com/dailydotdev","https://www.linkedin.com/company/daily-dev-ltd"]},{"@type":"WebSite","@id":"https://daily.dev/#website","url":"https://daily.dev","name":"daily.dev","publisher":{"@id":"https://daily.dev/#organization"},"potentialAction":{"@type":"SearchAction","target":{"@type":"EntryPoint","urlTemplate":"https://daily.dev/search?q={search_term_string}"},"query-input":"required name=search_term_string"}}]} {"@context":"https://schema.org","@type":"TechArticle","headline":"Replit — We Built a Video Rendering Engine by Lying to the Browser About What Time It Is","url":"https://daily.dev/posts/replit-we-built-a-video-rendering-engine-by-lying-to-the-browser-about-what-time-it-is-8jyaegwtp","mainEntityOfPage":{"@type":"WebPage","@id":"https://daily.dev/posts/replit-we-built-a-video-rendering-engine-by-lying-to-the-browser-about-what-time-it-is-8jyaegwtp"},"datePublished":"2026-03-03T13:59:45.703Z","dateModified":"2026-03-03T14:00:13.449Z","description":"Replit built a video rendering engine that captures arbitrary web pages as deterministic MP4 videos by virtualizing browser time. The system injects a...","image":"https://media.daily.dev/image/upload/f_auto,q_auto/v1/posts/e760d9ddd5564d1877f61a8404a1dd01?_a=AQAEuop","thumbnailUrl":"https://media.daily.dev/image/upload/f_auto,q_auto/v1/posts/e760d9ddd5564d1877f61a8404a1dd01?_a=AQAEuop","isAccessibleForFree":true,"articleSection":"Hacker News","inLanguage":"en","publisher":{"@type":"Organization","name":"daily.dev","url":"https://daily.dev","logo":{"@type":"ImageObject","url":"https://daily.dev/apple-touch-icon.png","width":180,"height":180}},"author":{"@type":"Organization","name":"Hacker News","logo":"https://media.daily.dev/image/upload/t_logo,f_auto/v1/logos/hn","url":"https://daily.dev/sources/hn"},"commentCount":0,"discussionUrl":"https://daily.dev/posts/replit-we-built-a-video-rendering-engine-by-lying-to-the-browser-about-what-time-it-is-8jyaegwtp","interactionStatistic":[{"@type":"InteractionCounter","interactionType":{"@type":"LikeAction"},"userInteractionCount":0},{"@type":"InteractionCounter","interactionType":{"@type":"CommentAction"},"userInteractionCount":0}],"keywords":"webdev,backend,crawling","timeRequired":"PT9M"} {"@context":"https://schema.org","@type":"BreadcrumbList","itemListElement":[{"@type":"ListItem","position":1,"name":"Home","item":"https://daily.dev"},{"@type":"ListItem","position":2,"name":"Hacker News","item":"https://daily.dev/sources/hn"},{"@type":"ListItem","position":3,"name":"Replit — We Built a Video Rendering Engine by Lying to the Browser About What Time It Is"}]} ```