ISOBMFF Audio

isobmff-audio is a library that wraps audio into the ISO Base Media File Format (MPEG-4 Part 12) (commonly referred to as Fragmented MP4 or fmp4).

• API
  • ISOBMFFAudioWrapper
    • Takes in audio (MP3, AAC, OGG Flac, or OGG Opus) and outputs fragmented ISOBMFF
• Demo
  • React application that demonstrates ISOBMFFAudioWrapper being used to support the MediaSource Extensions API with icecast-metadata-js
  • Checkout the demo here!

---

API

ISOBMFFAudioWrapper

https://github.com/eshaz/isobmff-audio/tree/master/src/ISOBMFFAudioWrapper.js

A class that takes in audio (MP3, AAC, OGG Flac, or OGG Opus) and outputs fragmented ISOBMFF.

Usage

1. To use ISOBMFFAudioWrapper, create a new instance of the class by passing in the mimetype of your audio data.

   Note: For directly converting from an HTTP response, use the mimetype contained in the Content-Type header

    import ISOBMFFAudioWrapper from "isobmff-audio";
    
    const headers = myHTTPResponse.headers;
    const mimeType = headers.get('Content-Type');
    
    const fmp4Wrapper = new ISOBMFFAudioWrapper(mimeType);
    

2. To wrap audio into ISOBMFF, pass in the raw audio data into the instance's .iterator(). Iterate over this iterator using a for ...of or for await...of loop. Repeat this step until all audio data has been read.

    const audioData = response.body;
    
    for (const fMP4 of fmp4Wrapper.iterator(audioData)) {
      // Do something with the wrapped data
    }
    

• ISOBMFFAudioWrapper will store any partial data until a full audio frame can be appended as ISOBMFF.

  Note: Any data that does not conform to the instance's mimetype will be discarded.

• Once enough data has been received to form at least 4 complete audio frames, and 1022 bytes of audio data, the initial segment will be returned along with a movie fragment containing the audio data. These values are user configurable using the options parameter in the constructor.

  • 1st Iteration

    "initial segment"
    --ftyp [file type]
    --moov [movie]
    "fragment"
    --moof [movie fragment]
    --mdat [audio data]
    

• Subsequent iterations will only return movie fragments.

  • nth Iteration

    "fragment"
    --moof [movie fragment]
    --mdat [audio data]
    

Methods

const wrapper = new ISOBMFFAudioWrapper("audio/mpeg", {minFramesPerFragment: 2, minBytesPerFragment: 576});

• constructor
  • Creates a new instance of ISOMBFFAudioWrapper that can be used to wrap audio for a given mimetype.
  • Parameters:
    • mimetype required Format of the audio to wrap into ISOBMFF
      • MP3 - audio/mpeg
      • AAC - audio/aac, audio/aacp
      • FLAC - audio/flac
      • Ogg FLAC - application/ogg, audio/ogg
      • Ogg Opus - application/ogg, audio/ogg
    • options optional
      • options.minFramesPerFragment optional Minimum audio frames to store before returning a fragment
        • Accepts an integer greater than 0
        • Defaults to 4
      • options.minBytesPerFragment optional Minimum audio bytes to store before returning a fragment
        • Accepts an integer greater than 0
        • Defaults to 1022
• wrapper.iterator(data)
  • Returns an Iterator that can be used in a for ...of loop to return ISOBMFF
  • Parameters:
    • data Uint8Array of audio data to wrap
• wrapper.mimeType
  • Getter that returns the mimeType of the wrapped audio data
    • For OGG, the codec is embedded in the first OGG page. This returns audio/mp4;codecs="flac,opus before that first page is read.
  • Examples:
    • MP3 - audio/mp4;codecs="mp3"
    • AAC - audio/mp4;codecs="mp4a.40.2"
    • FLAC - audio/mp4;codecs="flac"
    • OPUS - audio/mp4;codecs="opus"

---

Demo

isobmff-audio is used in the demo for icecast-metadata-js to allow for Icecast metadata support in Firefox (mp3, aac, flac) and Chrome (flac) by wrapping the streaming audio in ISOBMFF so it can be used with the MediaSource API.

https://github.com/eshaz/icecast-metadata-js/tree/master/src/demo

View the live demo here: https://eshaz.github.io/icecast-metadata-js/