trynoice/november

Various tests we performed to achieve gapless transition between two or more MP3 tracks in modern browsers.

Noice November

Various tests we performed to achieve gapless transition between two or more MP3 tracks in modern browsers.

What did we try?

Howler.js

Branch: https://github.com/trynoice/november/tree/test/howler

Howler.js supports playback using both the HTML5 Media Elements and Web Audio API. However, Howler.js doesn't have a built-in playlist API. Creating a rudimentary playlist API on top of Howler.js resulted in failure using both playback methods.

Gapless-5

Gapless-5 uses both HTML5 Media Elements and Web Audio API. It uses HTML5 Media Elements to start playback as soon as enough data is available and seamlessly switches it to Web Audio once it finishes loading the resource. It, however, didn't provide a gapless transition when moving from one playlist item to another.

HTML5 Audio API

Branch: https://github.com/trynoice/november/tree/test/html5-audio

It is a high-level audio API available in modern browsers. Since it is high level, its callbacks lag, and thus, we cannot use them to implement a seamless switch between two tracks.

To work around this issue, we buffered two HTMLAudioElements together. We used timeupdate events on the first track to pause it about 350 milliseconds before it ended and play the next (already buffered). It effectively produced a seamless transition between the two audios in Google Chrome but didn't work for Firefox, Microsoft Edge or the Chromium instance running on Chromecast v1.

Reference: https://stackoverflow.com/questions/7330023/gapless-looping-audio-html5

Web Audio API

Branch: https://github.com/trynoice/november/tree/test/web-audio-api

It is the lowest level audio API available in the browser. Its first limitation is that it doesn't support data streaming. It only supports decoding the entire resource at once. Since our MP3s are usually longer than a minute, holding decoded PCM data in memory wouldn't work since we want to play multiple tracks at once.

To overcome this limitation, we turned to aurora.js. The project seemed dead, but we forked the relevant repositories and made it work for WAV. However, we couldn't make its MP3 decoder work. Starting and stopping audio decoding at our will is another issue we couldn't resolve.

It is the closest we came to achieve gapless playback. We used aurora.js to decode the WAV file chunk by chunk. We then used the Web Audio API to queue decoded PCM chunks in an AudioContext. When a resource finished buffering, we moved on to the next one in the playlist and repeated the process.

Media Source Extensions

Branch: https://github.com/trynoice/november/tree/test/mse

We segmented input MP3 files into several chunks, like HLS/DASH. However, MP3 only worked with MSE in Chromium based browsers, and it didn't provide seamless transition from one chunk to the next.

We also tried FMP4 with AAC codec. It didn't work when we wrote two different media items to the same source buffer.

License

GNU GPL v3

White Noise icon by Juraj Sedlák