Developer builds browser-only MOV to MP4 converter that never uploads your file

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A developer has released movconverter, an open-source TypeScript library that converts MOV files to MP4 entirely within the browser, with no server uploads or file size restrictions. The tool exploits the fact that MOV and MP4 share the same underlying file format ancestry, meaning iPhone and Mac footage — already encoded in compatible H.264/HEVC and AAC formats — can be converted by rewriting metadata rather than re-encoding media. For less common cases involving PCM audio or ProRes video, the library falls back to WebCodecs or lazily loaded WebAssembly for transcoding. A free web interface is available at movtomp4.net, where users can drop in a file and complete the conversion locally without leaving the browser tab. The library also performs a preflight check before conversion, informing users in advance whether their file will be processed losslessly in seconds or require a slower audio transcode.

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