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ErickWendel/semana-javascript-expert08
JS Expert Week 8.0 - 🎥Pre processing videos before uploading in the browser 😏
A workshop repo from a Brazilian JavaScript educator covering in-browser video pre-processing using WebCodecs, MP4Box.js, and Web Workers before upload. Each lesson folder (aula01, aula02) is a self-contained snapshot of the codebase at that point in the course, so the repo is really a tutorial artifact rather than a reusable library.
Uses WebCodecs API correctly — demuxing MP4 via MP4Box.js, feeding decoded frames to a canvas renderer in a Worker, and muxing output WebM chunks, which is the right architecture for keeping the main thread unblocked. The lesson-by-lesson folder structure makes it easy to diff what changed between sessions. The server-side upload handler in aula02 shows how to stream multipart chunks without buffering the whole file in memory. Vendoring mp4box.0.5.2.js and webm-writer2.js means the demo runs without a build step.
This is course material, not production code — the checklist in the README is still full of unchecked items (360p/720p encoding, audio track handling, WebM duration bug) and the challenges are explicitly left for students. Browser support for WebCodecs is still Chromium-only; Firefox and Safari users get nothing, and there's no fallback or detection. The vendored mp4box is pinned to 0.5.2 from 2021 and is just dropped as a script file with no way to update it short of manually replacing it. Audio is completely ignored in the pipeline, so any video with audio comes out silent.