Firefox Beta 15 supports the new Opus audio format

Firefox Beta logo

Firefox 15 (now in the Beta channel) supports the Opus audio format, via the Opus reference implementation.

What is it?

Opus is a completely free audio format that was recently approved for publication as a standards-track RFC by the IETF. Opus files can play in Firefox Beta today.

Opus audio codec logo

Opus offers these benefits:

  • Better compression than MP3, Ogg, or AAC formats
  • Good for both music and speech
  • Dynamically adjustable bitrate, audio bandwidth, and coding delay
  • Support for both interactive and pre-recorded applications

Why Should I care?

First, Opus is free software, free for everyone, for any purpose. It’s also an IETF standard. Both the encoder and decoder are free, including the fixed-point implementation (for mobile devices). These aren’t toy demos. They’re the best we could make, ready for serious use.

We think Opus is an incredible new format for web audio. We’re working hard to convince other browsers to adopt it, to break the logjam over a common <audio> format.

The codec is a collaboration between members of the IETF Internet Wideband Audio Codec working group, including Mozilla, Microsoft, Xiph.Org, Broadcom, Octasic, and others.

We designed it for high-quality, interactive audio (VoIP, teleconference) and will use it in the upcoming WebRTC standard. Opus is also best-in-class for live streaming and static file playback. In fact, it is the first audio codec to be well-suited for both interactive and non-interactive applications.

Opus is as good or better than basically all existing lossy audio codecs, when competing against them in their sweet spots, including:

General audio codecs (high latency, high quality)
  • MP3
  • AAC (all flavors)
  • Vorbis
Speech codecs (low latency, low quality)
  • G.729
  • AMR-NB
  • AMR-WB (G.722.2)
  • Speex
  • iSAC
  • iLBC
  • G.722.1 (all variants)
  • G.719

And none of those codecs have the versatility to support all the use cases that Opus does.

Listening tests show that:

That’s a lot of bandwidth saved. It’s also much more flexible.

Opus can stream:

  • narrowband speech at bitrates as low as 6 kbps
  • fullband music at rates of 256 kbps per channel

At the higher of those rates, it is perceptually lossless. It also scales between these two extremes dynamically, depending on the network bandwidth available.

Opus compresses speech especially well. Those same test results (slide 19) show that for fullband mono speech, Opus is almost transparent at 32 kbps. For audio books and podcasts, it’s a real win.

Opus is also great for short files (like game sound effects) and startup latency, because unlike Vorbis, it doesn’t require several kilobytes of codebooks at the start of each file. This makes streaming easier, too, since the server doesn’t have to keep extra data around to send to clients who join mid-stream. Instead, it can send them a tiny, generic header constructed on the fly.

How do I use it in a web page?

Opus works with the <audio> element just like any other audio format.

For example:

 <audio src="ehren-paper_lights-64.opus" controls>

This code in a web page displays an embedded player like this:

Paper Lights by Ehren Starks Creative Commons License

(Requires Firefox 15 or later)

Encoding files

For now, the best way to create Opus files is to use the opusenc tool. You can get source code, along with Mac and Windows binaries, from:

While Firefox 15 is the first browser with native Opus support, playback is coming to gstreamer, libavcodec, foobar2000, and other media players.


Live streaming applications benefit greatly from Opus’s flexibility. You don’t have to decide up front whether you want low bandwidth or high quality, to optimize for voice or music, etc. Streaming servers can adapt the encoding as conditions change—without breaking the stream to the player.

Pre-encoded files can stream from a normal web server. The popular Icecast streaming media server can relay a single, live Opus stream, generated on the fly, to thousands of connected listeners. Opus is supported by the current development version of Icecast.

More Information

To learn more visit, or join us in #opus on

About Timothy B. Terriberry

Timothy B. Terriberry is a long-time volunteer for the Xiph.Org foundation, working on codecs such as Theora, Vorbis, CELT, and Opus. He has been contributing to Mozilla's media support since 2008 and hacking on WebRTC since 2010.

More articles by Timothy B. Terriberry…


  1. Henri Sivonen

    “Better compression than” … “Ogg” should probably say “Vorbis” instead of “Ogg”.

    July 19th, 2012 at 22:33
    1. Bernd

      “Better compression than […] Ogg […] formats” – In the family of “Ogg formats” there is also Speex as a codec that covers some of Opus’ use cases. The sentence just doesn’t mention Vorbis explicitly. But the family name of Vorbis may be more popular anyway…

      July 20th, 2012 at 20:48
  2. Giuseppe Bilotta

    The sample works perfectly in Opera 12 already.

    July 20th, 2012 at 00:05
    1. Style Thing

      this is really good news! the more the better ^^

      July 20th, 2012 at 09:41
    2. Bernd

      I can’t reproduce using Opera 12.00.1467/Presto 2.10.289 or 12.50.1513/Presto 2.11.310 on Ubuntu 11.10 32bit (gst-plugins-bad v0.11.92 installed); heard of somebody else failing, too.
      No word on Opus on official website on Opus codec.

      July 21st, 2012 at 09:45
      1. Bernd

        er – gst-plugins-bad v0.10.23, of course.

        July 21st, 2012 at 10:33
    3. Bernd

      Now that I’ve installed libopus and fixed my GStreamer installation it works for me too.

      So, support is not built in; they use different external backends and support whatever they support, it seems:

      July 24th, 2012 at 06:30
  3. Anonymous

    Any plans to support Opus audio in a video container along with VP8 or similar? Any plans for a new revision of WebM?

    July 20th, 2012 at 15:49
    1. Bernd

      Since the container format of WebM is a subset of Matroska we first need Matroska to work with Opus. That is being worked on:

      July 20th, 2012 at 20:21
  4. Jean-Marc Valin

    At this point, I’m not aware of any plans for Opus in WebM, though we never know. Technically, even if Opus was 50% more efficient than Vorbis, the total saving when counting video wouldn’t be that big. Of course, when we look into a new standard Opus would really make sense. For something like WebM, the main reason I would see to move to Opus would be about convenience, e.g. if there was a use-case for recording webrtc video that’s already encoded with VP8+Opus.

    July 20th, 2012 at 19:16
  5. Wolfgang

    Zeitstempel: 21.07.2012 13:32:21
    Warnung: Medien-Ressource konnte nicht dekodiert werden.
    Zeile: 0

    with Firefox 15.0b1 for me

    July 21st, 2012 at 04:33
  6. bubba

    I’m running Opera 12.00.1467 on Debian testing and the audio clip played OK. I have the base/good/bad/ugly/ffmpeg gstreamer plugins installed.

    July 21st, 2012 at 14:02
  7. Wolfgang Keller

    Unluckily the multichannel test vectors from
    (linked from don’t work. Please fix this bug.

    This said: great job.

    July 21st, 2012 at 16:15
    1. Ralph Giles

      We’ll fix the bug. Multichannel support is scheduled for Firefox 17, and should be out in December. Firefox 15 and 16 only support stereo and mono files.

      July 25th, 2012 at 13:00
  8. PuX

    after reading all this I can understand flexibility is the strong point of this new codec, but why exactly would anyone use this for streaming music instead of any other lossy codec with the objective of making it sound better? why not just go for lossless?

    July 21st, 2012 at 18:07
    1. sear

      For streaming purposes, better sound at lower bitrates is always a good thing. To my knowledge, HE-AAC is considered the streaming gold standard right now. The claim that this codec bests it is great news!

      July 22nd, 2012 at 22:43
    2. Bernd

      Some people sometimes have to meet various bitrate constraints. With internet radio often your server has limited capacity – so with Opus you can serve more people. And users sometimes have internet lines that can’t handle CD-quality FLAC streams.
      And then you sometimes have varying network conditions and you can adapt to these on the fly with Opus.

      Opus creates a lot of new possibilities – and for some people they are useful sometimes. If FLAC is for you, go for it. If you come across constraints like the described ones you may want to remember Opus…

      July 24th, 2012 at 07:08
      1. PuX

        I can see your point. Almost forgot that sometimes internet connection is so bad that it can’t handle 1000 kbps, which would be enough for usual cd-audio quality. So, yeah. If this codec can efficiently adjust the bitrate on the fly, I can see why this is cool.

        July 26th, 2012 at 16:47
        1. panzi

          In what kind of utopia do you live where you have a 1000 kbps connection? 250 kbps is standard here.

          September 11th, 2012 at 17:59
          1. Steve

            I’ve got a 17mbps connection. (Bog standard ADSL2+).

            (aka 2mbps, 2000kbps)

            200kbps is ISDN territority. Dialup is 56kbps.

            I think you’re confusing your K’s with your k’s.

            September 12th, 2012 at 18:46
          2. Ouch

            You mean ‘B’s with his ‘b’s
            Byte = 8 bits right?

            When you download, the browser tells you KBytes/sec. When you play, the player tells you KBits/sec, and when you pick an internet plan, they show you KBits/sec.

            Y u no make one standard?

            November 13th, 2012 at 21:52
  9. austin
    just what i thought of when reading this…

    July 24th, 2012 at 07:01
    1. Bernd

      The writers were thinking of that too. Have you noticed the link behind “break the logjam”?.. ;-)

      July 24th, 2012 at 07:12
      1. austin

        totally didnt…

        July 27th, 2012 at 08:10
  10. kizi

    this is really good news! the more the better ^^

    July 26th, 2012 at 15:19
  11. Caspy7

    Is there any work going on to get support into Android?

    August 2nd, 2012 at 17:09
    1. Bernd

      I think so: Support in Rockbox is underway:
      With “Rockbox as an Application” (RaaA, you should then be able to play Opus on Android.

      August 13th, 2012 at 08:46
      1. Caspy7

        This I understood, but that’s not quite the same as getting native support in Android.

        August 13th, 2012 at 08:58
        1. pow

          Opus works for me on Firefox Beta on Android, at least over wi-fi. The Android version is Gingerbread that came with the phone.

          August 26th, 2012 at 19:50
  12. pd

    Tried the encoder, very fast, very good sound at 256 CBR. Also appears to compress well. I got a result of an 82% reduction from a wav file (Morning Mr Magpie by Radiohead) and the sound was excellent. I used the –music profile naturally.

    I’d also like to see Firefox on Android support this codec. Perhaps Aurora for mobile already does?

    August 2nd, 2012 at 21:33
    1. pow

      Firefox Beta on Gingerbread plays the Opus sample in the article for me. (Tested over wifi).

      August 26th, 2012 at 19:52
  13. sylock


    I’m curious, is there any plan to support some kind of encryption of something like this. I explain why. I’m using Deezer because I like searching for some music and listen to it quickly and from everywhere.

    I read that Deezer changed their interface to fit html5 except for audio flow which use Flash since nothing except Flash can handle encryption and so “guarantee” them that the music won’t be copyied.

    I really want to see something else replacing that feature of Flash to be able to use Deezer without the flash plugin installed.
    I’m talking about my use case but I suppose I’m not the only want ;)

    September 4th, 2012 at 07:35
  14. Ralph Giles

    We have no plans to implement content scrambling for media streams. Such techniques are mostly useful to limit user action and create lock-in, which is counter to our mission.

    Mozilla will likely implement the MediaSource api, or something like it, which would permit websites to implement their own over-the-wire transforms, control buffering, report more accurate transit statistics and so on.

    September 4th, 2012 at 13:01
  15. sylock

    So if I understand well, media source is like an extension of the current html5 video and audio tags?

    September 4th, 2012 at 22:31
    1. Ralph Giles

      That’s right. It’s an extra interface on the video and audio tags that lets you feed compressed data streams from local javascript rather than directly from your server. A bit like the AppendBytes method in ActionScript.

      September 11th, 2012 at 21:51

Comments are closed for this article.