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0021. One export engine: the player in Chrome ​

Supersedes 0015 and the "chosen per file" part of 0019. The export is the player again, as 0007 first said.

Context ​

After 0019 the export had two picture engines. Node drew most files on the CPU (the plan and painter on skia, overlays through Satori, FFmpeg encoders from node-av); headless Chrome drew files with <Three>, <Motion>, motion blur or declared shaders, through the real player. Every feature had to be built twice or refused in one engine: Satori read a subset of CSS, skia had no WebGL, a WOFF2 font worked in one and not the other, and the docs carried a list of what --engine node left out. The layout check measured overlays with Satori, so it could disagree with what the export drew. The parity suites existed only to keep the two from drifting apart.

Remotion renders in a browser too (screenshots of a Chrome page, encoded by FFmpeg). Diffusion Studio has one engine, in the browser, and runs it under Puppeteer on a server. Neither keeps a second renderer.

Decision ​

  • Chrome draws every export. renderVideo, renderStill and checkLayout all open the export page; the Node picture path (frame pipeline, overlay plane, workers) and its dependencies (skia-canvas, satori, node-av, @mediabunny/server and its patch) are gone. engine, --engine, --workers, --speed and --software are removed; --tabs renders pieces on several pages of one browser.
  • The sound is mixed in the page. The same mixPlan runs there, over PCM that WebCodecs decodes. Chrome encodes Opus; AAC and MP3 go through Mediabunny's WebAssembly encoders (Chrome for Testing ships neither), and WAV is PCM. Node copies the encoded soundtrack into the file beside the joined pictures, or writes it alone for MP3 and WAV.
  • What Chrome encodes. MP4 holds H.264 or AV1, WebM holds VP9 or AV1. ProRes, HEVC, VP8 and .mov are dropped.
  • The layout check draws each overlay alone in the page (the others hidden), captures it and reads its ink, so it measures what the export draws.
  • The export downloads its browser. The first export downloads Chrome for Testing (milestone 157, the one CI tests) into ~/.cache/cutcraft/browsers with @puppeteer/browsers; cutcraft browser install does it ahead of time and CUTCRAFT_CHROMIUM names another binary. playwright-core is a dependency, not an optional peer.
  • Smart copy stays, for VP9 into VP9, with the overlay check now in the kit and player rather than in the Node overlay plane.

Consequences ​

  • One engine: what the preview draws is what the export draws, including any CSS in a <Layer>, WOFF2 fonts, shaders and overlay effects. The "left out in the Node export" warnings and their docs are gone.
  • Every export needs Chrome: about one download per machine, and a few seconds to start it per export.
  • Without a GPU, Chrome draws on the CPU (SwiftShader for WebGL). Files the Node engine drew fast (plain cuts at 111 fps on a 4-core Linux runner) are slower now. The export-speed page, which compared the Node engine with Remotion and Diffusion Studio, was removed for "How the export works" (docs/guide/export-architecture.md). --copy and --tabs are the levers meanwhile.
  • The tests that render live in the browser suite (test:browser), which CI runs in the e2e job with the downloaded Chrome; pnpm test keeps the parts that need no browser. The tests read exports back with ffmpeg and ffprobe.

Alternatives ​

Keeping Node for the files it can draw: the speed stays, and so does every feature built twice. Moving Node to a GPU canvas (skia-canvas with GPU, or headless WebGL in Node): still a second renderer to keep equal to the player. Screenshots and FFmpeg as Remotion does: slower than capturing in the page with drawElementImage and encoding with WebCodecs, and FFmpeg comes back as a dependency.

MIT licensed.