mp4craft

TypeScript-first, zero-dependency MP4 muxer designed for the browser.

What is mp4craft?

mp4craft takes pre-encoded video and audio samples and writes them into a valid MP4 file. It covers every codec and every container layout the format defines for the web, with zero runtime dependencies.

import { ArrayBufferTarget, Mp4Muxer } from 'mp4craft'

const target = new ArrayBufferTarget()
const muxer = new Mp4Muxer({
  target,
  fastStart: 'in-memory',
  video: { codec: 'avc', width: 1280, height: 720, description: avccBytes },
})

muxer.addVideoChunk(encodedChunk)
await muxer.finalize()

const mp4 = new Uint8Array(target.buffer)

Features

• Video codecs: AVC, HEVC, VP9, AV1
• Audio codecs: AAC-LC, Opus, MP3, FLAC, integer PCM
• Container layouts: progressive, in-memory fast start, fragmented
• Targets: ArrayBufferTarget, StreamTarget, or a custom Target
• WebCodecs-native, with a raw-sample API for Node.js encoders
• Zero runtime dependencies

Installation

npm install mp4craft
# or
pnpm add mp4craft
# or
yarn add mp4craft

Quick start

Mux video with audio

import { Mp4Muxer, ArrayBufferTarget } from 'mp4craft'

const muxer = new Mp4Muxer({
  target: new ArrayBufferTarget(),
  fastStart: 'in-memory',
  video: { codec: 'avc', width: 1280, height: 720, description: avccBytes },
  audio: { codec: 'aac', channels: 2, sampleRate: 48000, description: aacBytes },
})

for (const videoChunk of encodedVideoChunks) {
  muxer.addVideoChunk(videoChunk)
}
for (const audioChunk of encodedAudioChunks) {
  muxer.addAudioChunk(audioChunk)
}

await muxer.finalize()

Stream to disk with backpressure

import { Mp4Muxer, StreamTarget } from 'mp4craft'
import { createWriteStream } from 'node:fs'
import { once } from 'node:events'

const writeStream = createWriteStream('output.mp4')

const target = new StreamTarget({
  onData: async ({ data }) => {
    if (!writeStream.write(data)) {
      await once(writeStream, 'drain')
    }
  },
  onFinish: () =>
    new Promise<void>((resolve, reject) => {
      writeStream.end((error?: Error | null) => (error ? reject(error) : resolve()))
    }),
})

const muxer = new Mp4Muxer({
  target,
  fastStart: 'in-memory',
  video: { codec: 'avc', width: 1920, height: 1080, description: avccBytes },
})

for (const rawSample of encodedVideoSamples) {
  muxer.addVideoSample(rawSample)
}
await muxer.finalize()

Fragmented MP4 for live streaming

import { Mp4Muxer, StreamTarget } from 'mp4craft'

const muxer = new Mp4Muxer({
  target: new StreamTarget({
    onData: ({ data }) => sourceBuffer.appendBuffer(data),
  }),
  fastStart: 'fragmented',
  video: { codec: 'avc', width: 1280, height: 720, description: avccBytes },
})

Documentation

Visit the Docs for comprehensive guides, examples and API documentation.

Playground

Visit the Playground to see mp4craft in action.

License

mp4craft is open-source software licensed under the MIT License.