@audio/decode-mp4

Decode the audio track of MP4, MOV, M4A, M4V and 3GP files to PCM float samples. A pure-JS ISO BMFF demuxer that skips the video track and routes the audio (AAC, ALAC, MP3, FLAC, Opus, AC-3, DTS, AMR, PCM) to the matching codec package, loaded on demand.

import decode, { decoder } from '@audio/decode-mp4'

let { channelData, sampleRate } = await decode(mp4Bytes)

let dec = await decoder()
let head = await dec.decode(chunk1)   // Promise on the chunk that completes the track header
let more = dec.decode(chunk2)         // synchronous from then on
let tail = await dec.flush()
dec.free()

Codecs

| Sample entry | Codec | Decoded by | |---|---|---| | mp4a (esds object type 0x40, 0x66–0x68) | AAC-LC, HE-AAC v1/v2 | @audio/decode-aac | | alac | Apple Lossless | @audio/decode-aac (pure JS) | | mp4a (0x69, 0x6B), .mp3 | MP3 | @audio/decode-mp3 | | fLaC | FLAC | @audio/decode-flac | | Opus | Opus | @audio/decode-opus | | samr, sawb | AMR-NB, AMR-WB | @audio/decode-amr | | sowt, twos, in24, in32, fl32, fl64, lpcm, ipcm, fpcm, raw , NONE | PCM 8–32 bit int, 32/64 bit float, either endianness | built in | | ulaw, alaw | G.711 | built in | | ac-3, mp4a (0xA5) | AC-3 | @audio/decode-ac3 | | dtsc, dtsh, dtsl, dtse, mp4a (0xA9) | DTS (core) | @audio/decode-dts | | ec-3, mp4a (0xA6) | E-AC-3 (Dolby Digital Plus) | @audio/decode-eac3 |

TrueHD tracks throw an error naming the codec. Fragmented MP4 (ISO/IEC 14496-12 §8.8, moof+mdat after an empty-table moov) streams fragment by fragment, holding only the bytes not yet read. QuickTime sound descriptions v0, v1 and v2 are handled, including wave-wrapped configs and enda endianness flags. When moov follows mdat (typical of camera and QuickTime output) the file is buffered until the header arrives.

Codec packages are imported dynamically, which is unavailable inside an AudioWorklet — decode in the main thread or a Worker.

API

decode(src: Uint8Array | ArrayBuffer): Promise<AudioData>

Decode a complete file.

decoder(): Promise<MP4Decoder>

Streaming decoder. decode(chunk) returns AudioData, or a Promise of it on the chunk that completes the track header while the codec module loads. flush() returns remaining samples and throws if no audio track was found. free() releases codec resources.

AudioData

{ channelData: Float32Array[], sampleRate: number }

License

ॐ · MIT. Codec packages carry their own licenses.