mp4‑stream is a Node.js library that provides streaming‑style encoding and decoding of MP4 files. It lets developers treat an MP4 as a sequence of “boxes,” emitting events for each box and offering APIs to ignore, stream, or fully decode its contents, as well as to construct new boxes and write media data on the fly. The package is aimed at JavaScript developers who need to process or generate MP4 video/audio data in a memory‑efficient, pipe‑compatible way.