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Vanilagy/mp4-muxer
MP4 multiplexer in pure TypeScript with support for WebCodecs API, video & audio.
A pure TypeScript MP4 muxer built around the WebCodecs API, letting you write MP4 files in the browser without native dependencies. It's now deprecated — the author has moved on to Mediabunny, which supersedes it entirely.
The deprecation notice is honest and immediate, with a migration guide and clear pointers to the successor. The source is small and readable — six files in src/ covering box writing, muxing, and output targets. No native deps, works in-browser with WebCodecs. The prebuilt artifacts in build/ mean you can drop it in without a bundler.
Deprecated and unmaintained as of late 2025 — any bug you hit stays a bug. No test harness worth mentioning, just two HTML test pages. There is no streaming demux or remux path — write-only. If you're starting fresh, there is no reason to pick this over Mediabunny.