Opus Format

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Winnow
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Opus Format

Post by Winnow »

Anyone familiar with it? Sounds like it might be nice to have support for it soon. Firefox b15 has it.
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:

At 64 kbps, Opus sounds better than both HE-AAC and Vorbis.
A 64 kbps Opus file sounds as good as a 96 kbps MP3 file.

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.
Looks like Opera is on board now or soon and Microsoft is mentioned as being part of Internet Wideband Audio Codec working group so I'd guess IE will have it. That pretty much just leaves Chrome. Safari doesn't count.
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