Can WebM Files Have Multiple Audio Tracks?

This article explores the technical capabilities of the WebM file format regarding multiple audio tracks. While the WebM specification natively supports hosting more than one audio stream within a single container, real-world implementation is heavily dictated by web browser compatibility and media player support. Below, we break down how WebM handles multiple audio tracks, the underlying technology, and the current limitations you might face when deploying them online.

The Technical Structure of WebM

The WebM container is based on the Matroska (MKV) profile. Because it inherits this architecture, WebM is inherently capable of multiplexing (muxing) several tracks into a single file. This means you can technically package a video track alongside:

Language Dubs: English, Spanish, and Japanese audio tracks in the same file.
Audio Descriptions: A dedicated track for visually impaired users.
Director’s Commentary: An alternative secondary audio track.

The underlying audio codecs typically used in WebM—such as Opus and Vorbis—work perfectly fine when multiple instances are multiplexed together.

Browser and Player Compatibility Challenges

While creating a multi-track WebM file is straightforward using tools like FFmpeg, playing it back smoothly on the web is a different story. HTML5 video players and standard web browsers have uneven support for multi-audio containers.

Platform/Browser	Multi-Audio Support Status	Behavior
Google Chrome / Edge	Partial / Limited	Usually plays the first audio track by default; switching requires custom JavaScript.
Mozilla Firefox	Native Support	Offers a track selection interface in the native player controls.
Safari	Poor	Limited WebM support overall; multi-track handling is unreliable.
VLC Media Player	Full Support	Desktop media players handle multi-track WebM flawlessly.

Implementing Multi-Audio WebM on the Web

If you want to use a single WebM file with multiple audio tracks on a website, relying on the browser’s default HTML5 video controls is usually not enough. To ensure a good user experience, developers typically utilize the AudioTrackList API via JavaScript.

// Example of detecting and switching tracks via JavaScript
const video = document.querySelector('video');

if (video.audioTracks && video.audioTracks.length > 1) {
    // Disable the first track, enable the second track
    video.audioTracks[0].enabled = false;
    video.audioTracks[1].enabled = true;
}

Note: Because browser support for the audioTracks property is still inconsistent across the web ecosystem, many developers choose alternative methods. Instead of packaging multiple tracks into one WebM file, they stream separate audio files and sync them using JavaScript, or adopt advanced streaming protocols like DASH (Dynamic Adaptive Streaming over HTTP) or HLS.