mp3 support on Firefox MediaSourceExtension

Question

I'm looking into implementing adaptive and progressive audio streaming in the browser, with no plugins. MSE is the HTML5 API I was waiting for, available in FF 42, but it seems that the audio format support in Firefox is not there?... mp3 audio is not working when using the MSE APIs.

Here's a code snippet:

var mediaSource = new window.MediaSource();
var audioSourceBuffer;

mediaSource.addEventListener('sourceopen', function (e) {
    try {
        var mimeType = "audio/mpeg";
        audioSourceBuffer = mediaSource.addSourceBuffer(mimeType);
    } catch (e) {
        log('Exception calling addSourceBuffer', e);
        return;
    }
}

I get a NotSupportedError exception when calling addSourceBuffer.

Doesn't Firefox support mp3? from MDN list of supported formats (https://developer.mozilla.org/en-US/docs/Web/HTML/Supported_media_formats) it implies that mp3 support should be there if the OS supports it - and the OS I am testing on (OSX) does support it.

Any help appreciated!

Answer 1

OK, so I was able to figure it out with the kind help of Mozilla engineers working on Media Source Extension.

The first key thing to note on MSE (Media Source Extension) is that it does not necessarily support all media formats supported by the browser's Audio Element. To illustrate this, although Firefox will play mp3 file when fed directly to the browser or directly to an Audio element, it will not play the same mp3 file if you feed it into a media source buffer.

Now, which media format are actually supported by Firefox' MSE implementation? the answer is that as of Firefox 42 only fMP4 (Fragmented MP4) is supported by default. webm is also supported, but not by default and your users will have to turn it on manually through Firefox' about:config page. The fMP4 mimeType to feed the Media Source object when creating a new buffer is: audio/mp4; codecs="mp4a.40.2"

And if you're wondering what the heck is fMP4, it is a standard which is part of the MPEG-4 standard, more specifically part 12: "ISO Base Media File Format (ISOBMFF) using non-multiplexed audio/video". Look it up if you're interested in more details.

From my experience fMP4 is supported across all major browsers and OS - which makes fMP4 a good format candidate for adaptive and progressive streaming.

HTH!